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Key Points:

  • About 3% to 5% of cases of persistent diarrhea in travelers are caused by parasites. Giardiasis causes most cases of persistent diarrhea. Cryptosporidia and Cyclospora are other causes.

  • Rabies is most common in India, Philippines, and Africa.

  • Cholera rarely occurs in travelers. The vaccine is not licensed in the U.S., but is available in Canada, European Union countries, and Australia. It may be useful for people at high risk.

  • A single 1-gm dose of azithromycin is effective in the treatment of severe cholera in adults. This drug is also effective for treating cholera in children.

  • The greatest risk for typhoid fever is in the Indian subcontinent, South East Asia, and Far East Asia.

  • Neither the intramuscular polysaccharide typhoid vaccine or the oral live attenuated vaccine (Vivotif) protect against paratyphoid fever, and vaccine immunity to typhoid can be "overcome" by a high inoculating dose of the bacterium.

  • The maximum efficacy achieved by either of these vaccines is 75%, with cumulative three-year efficacies of 50-60%. Protection wanes with time, and boosters are needed every two-three years with the polysaccharide vaccine and every 5 years with the oral live vaccine.

  • The first-line treatment of visceral leishmaniasis is pentavalent antimony (meglumine antimoniate or sodium stibogluconate), but toxicity is frequent with this drug.

  • Pentavalent antimonial compounds remain the mainstay of treatment worldwide, except in India. During the past decade, short courses of lipid formulations of amphotericin B hae been assessed and proved effective; however, their cost precludes their wide use in developing countries. Miltefosine, an oral active agent, might fulfill expectations for an effective, safe, easily administered and affordable antileishmanial treatment.

  • Avian influenza A (H5N1) is predominantly a disease of birds. The virus does not pass easily from birds to people and does not to pass from person to person (except in very rare cases of close contact with an infected blood relative).

  • Leptospirosis occurs worldwide, but is most commonly reported in Hawaii, Malaysia, Borneo, Costa Rica, Brazil, and China. The diagnosis may be difficult to establish, but serologic tests can be done through the CDC.

  • Schistosomiasis is second only to malaria as the most prevalent tropical disease in the world: 200 million infected, with 20 million made seriously sick by those infections, and 20,000 dead each year because of "schisto," according to World Health Organization (WHO) estimates.

What's New

  • To date, no cases of avian influenza A (H5N1) illness have been identified among short-term travelers visiting countries affected by outbreaks among poultry or wild birds.

  • Amantadine and rimantadine are currently not recommended for use in the U.S. for treating the flu because almost all influenza A viruses are resistant to them, and they are not effective against influenza B viruses. When influenza A viruses predominate, however, these drugs may still be useful if they are used in combination with a neuraminidase inhibitor, such as oseltamivir (TamiFlu®).

  • An increasing proportion of influenza A (H1N1) viruses are resistant to oseltamivir, the oral neuraminidase inhibitor, but not to zanamivir (Relenza®). Zanamivir is a neuraminidase inhibitor that is administered by active inhalation, a method that may not be practical for debilitated patients or for younger children, and is contraindicated for those with reactive airway disease.

  • The CDC's Advisory Committee on Immunization Practices (ACIP) now recommends expanding the use of the nasal influenza vaccine LAIV (FluMist®) to include healthy children ages 2-4 years old (24–59 months old) without a history of asthma or recurrent wheezing. The vaccine continues to be recommended for healthy persons ages 5–49 years who are not pregnant. “Healthy” indicates persons who do not have an underlying medical condition that predisposes them to influenza complications.

  • Polio is spreading to new countries and increasing where it is endemic. Polio booster are recommended by the CDC (January 2013) for the following countries: Afghanistan, Angola,Benin, Burkina Fasso, Burundi, Cameroon, Central African republic, Chad, China, Congo, Democratic republic of the Congo, India, Iran, Mali, Niger, Nigeria, Pakistan, Rwanda, Sudan, Tajikistan, Tanzania, Turkmenistan, Uzbekistan, Uganda, Zambia

  • Liposomal amphotericin B (AmBisome); Gilead Science, Paris, France) seems to be less toxic than other amphotericin B lipid formulations (Amphocil);

Giardiasis

The parasite that causes giardiasis (Giardia lamblia) is found in contaminated water (and less frequently in food) and water as a result of fecal contamination from humans or animals (mostly dogs, beaver, and cattle). Giardiasis occurs worldwide, but a higher incidence has been reported in travelers returning from the Indian sub-Continent, Southeast Asia, and Indonesia. Although travelers to Mexico and Latin America and the countries in Asia and Africa may also acquire infection, fewer than 3% of travelers returning from these areas have been found to harbor Giardia parasites. Giardia cysts can be spread easily from person-to-person in households and in day care centers. Poor personal hygiene, lack of hand washing, and close physical contact, especially oral-anal sexual contact, promotes transmission.

Giardiasis is also known as "backpacker's diarrhea" because the parasites may be found in ponds, lakes, and streams in rural or mountainous areas, even in the U.S. and Canada, and pose a potential risk to campers and hikers drinking from these sources. Note: Published reports of confirmed giardiasis among outdoor recreationists in North America clearly demonstrate a high incidence among this population. However, the evidence for an association between drinking backcountry water and acquiring giardiasis is minimal. Person-to-person spread appears to be a more significant factor in acquiring backpacker's diarrhea, and perhaps more emphasis should be placed on hand washing, personal hygiene, and other behavior modifications during backcountry travel, rather than simply on water purification.

Symptoms can be sudden and severe or occur gradually. Some travelers may have no complaints except one large, loose bowel movement daily. Nausea, fatigue, weight loss, abdominal cramps, non-bloody diarrhea, excessive gas, abdominal rumblings (borborygmi) and bloating can also occur to varying degrees. A taste of “rotten eggs” is common. Fever is very rare in giardiasis. When the illness is persistent, symptoms may last for weeks or months and be passed off as indigestion, or irritable bowel syndrome. Some cases of chronic fatigue syndrome may be caused by giardiasis. Fatigue, out of proportion to the degree of diarrhea is frequent. In severe cases, malabsorption of food may lead to severe weight loss and malnutrition.

If you have diarrhea lasting more than 2 to 3 weeks, you should be tested for intestinal parasites. Most likely, your doctor will ask you to submit several stool samples for microscopic examination. Detecting Giardia parasites can be difficult because organisms are not constantly present in stool; therefore, if the microscopic examination is negative, a more invasive method, such as a small bowel biopsy, may be required. A very sensitive and specific noninvasive screening test of stool, the enzyme immunoassay, is also available. (GiardEIA Giardia lamblia Testing Kit; Antibodies Incorporated, Davis, California; 800-824-8540 or 530-758-4400; http://www.antibodiesinc.com). If the immunoassay test is negative, then giardiasis is unlikely. Less common intestinal parasites that can also cause chronic diarrhea include Dientamoeba fragilis, Isospora belli, Cryptosporidium, Cyclospora cayetanensis, and Entamoeba histolytica (the cause of amebiasis).

Treatment

The drug of choice is tinidazole (Tindamax). The dose in adults is 2 grams once daily. For children older than 3 years up to 40 kg in weight, the dose is 50mg/kg once daily.

Another new product, Nitazoxanide (Alinia), is now available as a liquid preparation for children 1 to 11 years of age. Under 4 years of age the dose is 1 teaspoon twice daily for 3 days and 2 teaspoons twice daily in those older than 4 years.

Single-dose metronidazole (2 gm in adults) administered with food at bedtime once daily for 3 days is as effective as the standard 5-day course of 250 mg three times daily. The single dose regimen for children less than 25 kg is 35 mg/kg (in a single dose daily for 3 days). For children who weigh 25 kg to 40 kg, the daily dose is 50 mg/kg for 3 days.

Alternative treatments include furazolidone, albendazole, and bacitracin zinc. Furazolidone (Furoxone), 100 mg four times daily for 7 to 10 days, is a good, but very expensive, alternative for several reasons: (1) it is available in a liquid preparation (useful for children), and (2) the drug is also effective against most bacterial causes of travelers' diarrhea, making furazolidone potentially useful as broad-spectrum treatment when the cause of the diarrhea is not known. (Note: The brand name drug is no longer available in the U.S. but generic forms may be available online or through your pharmacy.) Albendazole, 400 mg twice daily for 7 days (3 days is usually insufficient), is a safe alternative drug with a varying cure rate.

If you are in a remote area with symptoms compatible with giardiasis, and testing is not available, start treatment with one of the drugs above on the assumption that giardiasis is the probable cause of your diarrhea. If no improvement occurs, seek medical consultation as soon as possible. Note: Lactose intolerance frequently accompanies giardiasis and may persist for weeks or months following parasite eradication.

Prevention

There is no prophylactic drug or vaccine to prevent giardiasis. Follow the food, drink, and water disinfection guidelines as outlined in Chapter 5, but note that chlorine and iodine may not be effective against parasites. Hand washing and good personal hygiene are important measures.

invasive Amebiasis

This potentially serious illness is caused by Entamoeba histolytica, single-celled parasites that can invade the wall of the large intestine, causing either acute amebic colitis (amebic dysentery) or chronic diarrhea of varying severity. The parasites, occasionally, spread to the liver, resulting in amebic liver abscess. Other complications, which are rare, include rupture into the peritoneal cavity, pericarditis, and cerebral amebiasis. Invasive, symptomatic disease begins 2 days to 4 months after infection. In the carrier state, which is common, parasites reside in the intestine for months to years without causing symptoms.

Avoiding diagnostic confusion Stool microcscopy is not a reliable test for E. histolytica infection. Studies show that >90% of those with a possible E. histolytica infection are actually carrying a microscopically identical but harmless parasite called Entamoeba dispar, for which no treatment is necessary. The presence of the common, but benign E. dispar can result in misdiagnosis. Serum antibody tests can clarify the situation. If the serology (antibody) test for E. histolytica is negative, you can presume that the patient does not have invasive amebiasis but is only harboring E. dispar, seek another source of illness.

Testing the stool for E. histolytica E. histolytica antigen or DNA can be be detected by a stool test (TechLab E. histolytica II test kit. TECHLABS Inc., Blacksburg, VA; 540-953-1664; (http://www.techlab.com).

Transmission of amebiasis occurs through the ingestion of fecally contaminated food or water. Infected food handlers and houseflies can also spread the disease. Person-to-person contact is important in transmission; household members and sexual partners, especially men who have sex with men, can easily become infected.

Amebiasis is a very common infection worldwide but is distinctly rare in travelers. Infection is usually associated with longer-term stays (> 1 month) in highly endemic areas. High-risk areas (where up to one-half of the population carries the parasite) are India, West Africa and southern Africa, SE Asia, and Central and South America. It is seen in the United States, but primarily in refugees, immigrants, or migrant workers, often from Mexico.

Travelers who develop an amebic liver abscess (which is diagnosed with ultrasound) usually don't have diarrhea or other intestinal symptoms. Instead, they may note fever, right upper abdominal pain, and have an enlarged, tender liver. Sweating, chills, weight loss, and fatigue are usually present. Note: Amebic liver abscess is uncommon, even in long-term travelers.

A microscopic stool examination to identify trophozoites or amebic cysts will point toward the diagnosis, especially if red blood cells are detected within the parasites. Antibody tests are usually diagnostic, especially if an amebic liver abscess or colitis is suspected. Amebic dysentery must be distinguished from other infections causing bloody diarrhea (e.g., enterocolitis caused by shigella, campylobacter, salmonella, yersinia, or Clostridium difficile). Crohn disease and ulcerative colitis can mimic amebiasis and must be considered in the younger patient. In older persons, diverticulitis or malignancy should be suspected.

Treatment

The ideal treatment of invasive amebiasis (colitis or abscess) in the United States is now tinidazole (Fasigyn, Tindamax), 2 grams once daily for 3 days. Metronidazole, 750 mg, three times daily for 5 days or 2.5 grams once daily for 3 days, is also effective. Both regimens must be followed by a drug that acts in the lumen of the bowel such as iodoquinol, 650 mg, three times daily for 20 days, or paromomycin, 25-35 mg/kg/d by mouth three times daily for 7 days. This combined regimen cures 100% of those with amebic liver abscess and 93% of those with amebic colitis. Even a single dose of metronidazole (2.5 grams) is usually effective in curing an uncomplicated liver abscess. Asymptomatic cyst passers and those without documented invasive disease require iodoquinol alone. Asymptomatic cyst passers with a positive serology test (indicating microinvasive disease) may also require treatment with tinidazole or metronidazole.

Cholera

This disease is caused by Vibrio cholerae bacteria, commonly transmitted by contaminated food and water or by person-to-person contact. Cholera is often asymptomatic, but in heavy infections it sometimes causes life-threatening diarrhea, particularly among the indigenous people in developing countries. Severe diarrhea from cholera requires the ingestion of large numbers of bacteria, hence the severe form of the disease is rarely seen in healthy tourists who follow prudent dietary habits (and who have adequate gastric acid—a protective barrier to infection).

Cholera occurs both sporadically and in worldwide epidemics. Sub-Saharan Africa has the highest reported cholera incidence and mortality rates in the world. Over 100 countries report cases, but the disease is more widespread than officially recognized.

Cholera is basically a disease of poverty, and most illness occurs among those people in lesser-developed countries who are exposed to heavily contaminated water or food. Therefore, most travelers on a tourist itinerary need not worry about this disease. In fact, cholera is officially reported in only 1 in 500,000 returning travelers. The healthy people at risk of acquiring cholera disease usually work in high-risk environments, such as refugee camps or relief centers.

Unlike some microbes, cholera bacteria are readily killed by stomach acid. However, if you do ingest a large dose of bacteria from heavily contaminated water—or if you are taking antacids or antiulcer drugs—bacteria can get past the stomach and enter your small intestine. Cholera enterotoxin then acts on the intestinal wall to cause outpourings of water and salt into the gut.

The clinical picture of cholera varies widely. Seventy-five percent of infections are mild or without any symptoms. Only 2% to 5% of infections cause severe symptoms. Cholera in its most severe form is characterized by massive watery diarrhea, vomiting, and muscle cramps. Vomiting is common and may be severe. The frequent, watery stools soon lose all fecal appearance (“rice water stools”) and practically all odor. Loss of fluids and electrolytes can cause shock and death in hours if fluids are not replaced.

Milder cases of cholera can mimic travelers' diarrhea caused by toxigenic Escherichia coli, salmonella, intestinal viruses, and parasites. The absence of blood or pus in the stools, and the lack of fever, are distinguishing features of cholera.

Treatment

Cholera kills solely by dehydration. If you develop severe watery diarrhea, you should immediately start rehydration treatment. (Chapter 6)

Fluids Drinking an oral rehydration solution (ORS) is essential and its prompt use has saved many lives. ORS can be prepared from water, sugar, and salt or more conveniently, using packets of ready-mixed salts, e.g., CeraLyte. After rehydration, you should drink 8 to 12 ounces, or more, of full-strength rehydration solution after every loose stool. If your diarrhea is very profuse and exceeds the amount of fluids you can drink, or if you are vomiting and can't retain enough fluids, you may need to be hospitalized and treated with intravenous fluids. NOTE: Don't underestimate fluid requirements—some patients with severe watery diarrhea may require as much as 10 to 12 liters of fluid replacement daily.

Antibiotics Antibiotics will shorten the duration of illness and are an important adjunct to fluid therapy. In 2006, a study in the New England Journal of Medicine, reported that a single 1-gm dose of azithromycin was more effective than ciprofloxacin in the treatment of severe cholera. Other drugs thar are reported to be effective in a single oral dose include tetracycline (not to exceed 1 g), doxycycline (not to exceed 300 mg). ciprofloxacin (500 mg x 2 doses in 1 day), and levafloxacin (500 mg).

Note: A traveler who develops diarrhea won't know if it's due to cholera or some other bacterium and most likely will treat himself with the stand-by antibiotic prescribed by his health care provider before departure. My current practice at the Travel Medicine Center of Western Massachusetts is to provide the traveler with azithromycin, 500 mg, with instructions to take a single 2-tablet dose daily for up to three days. The first day's treatment is actually complete antibiotic treatment for this disease, but the traveler can take all three days (6 tablets) if symptoms persist. If diarrhea persists >3 days despite antibiotics, other causes of diarrhea need to be considered, in particular, parasites. Bloody diarrhea with fever and abdominal pain (dysentery) calls for medical consultation on a priority basis.

Treatment of children: Although the quinolones are generally contraindicated in children, single-dose therapy with these drugs is not harmful. Furazolidone and azithromycin are safe for children of all ages.

Prevention

Food and Drink Precautions The best prevention against cholera is to pay careful attention to what you eat and drink (Chapter 5). It is particularly important (1) to avoid raw or undercooked food and seafood (e.g., ceviche, raw shellfish), and (2) to drink only commercially bottled, boiled, filtered, or chemically disinfected water without ice.

Vaccination The manufacture and availability of the injectable cholera vaccine in the United States ceased in June 2000. New, oral, vaccines are now available, but only in Canada and Europe; they are not licensed in the United States. These vaccines are:

  • An oral, live attenuated cholera vaccine, (Mutacol® in Canada), is approved for use in adults and in children aged > 2 years. This vaccine is currently not available from the manufacturer (Berna).
  • An oral, inactivated cholera vaccine, Dukoral, was approved for use in Canada in 2003 and the European Union in 2004, for children aged ≥ 2 years and for adults. This vaccine comprises killed whole cell Vibrio cholerae (WC) and the non-toxic, recombinant cholera toxin B-subunit (BS). (Note: Through the BS component, the oral cholera vaccine, Dukoral™, has also been shown to provide some short-term protection against diarrhea caused by enterotoxigenic E. coli).

Efficacy: Protection Against Cholera (Dukoral™ only) A double-blind, placebo-controlled field trial in Peru (using the currently licensed recombinant BS component of the vaccine) demonstrated an efficacy of 86% against a cholera epidemic. Note: there is no efficacy against the O139 Bengal strain of cholera prevalent in India, Bangladesh and Southeast Asia.

Recommendations for use Because the risk of cholera is extremely low for the average traveler, cholera vaccine is usually recommended only for people, such as relief workers or health care personnel, who are working in a high-risk endemic area under less than adequate sanitary conditions, or travelers who work or live in remote, endemic or epidemic areas and who don't have ready access to medical care. See Ch. 3 for a discussion of the use of oral cholera vaccine to prevent travelers' (ETEC) diarrhea.

Typhoid Fever

Typhoid fever (sometimes called enteric fever) is a serious, sometimes life-threatening disease caused by one particular species of Salmonella bacteria (Salmonella typhi) and is contracted by the consumption of contaminated food or water, or by contact with an infected person. Untreated, typhoid lasts 2 to 6 weeks and is up to 30% fatal. However, with treatment mortality is less than 1%.

Although typhoid fever is found in all countries in the developing world, the highest disease rates are reported from Peru, Chile, Haiti, Nigeria, India, Pakistan, Southeast Asia, and Indonesia. Most cases of typhoid reported in American travelers originate in the Indian subcontinent or South America.

The early symptoms of typhoid fever usually consist of chills and fever, headache, weakness, loss of appetite, abdominal pain, body aches (myalgia), cough, and constipation. A rash, with pink spots measuring 2 to 4 mm, may appear on the chest and abdomen. There is a 50% occurrence of diarrhea, which is sometimes bloody in the second to third week of illness. Diarrhea occurs most often in children and in the second to third week of illness. In fact, if your doctor considers diarrhea a prerequisite for the diagnosis of this disease, the diagnosis may be missed. The usual method for diagnosing typhoid fever is a blood culture combined with a stool culture (40% to 80% positive). Although a bone marrow aspirate is more sensitive (80% to 95% positive), it is a more painful and invasive procedure.

Treatment

Strains of Salmonella typhi—resistant to ampicillin, trimethoprim/sulfamethoxazole, and chloramphenicol—have become increasingly prevalent, especially outside Latin America (where these drugs may still be effective). The fluoroquinolones (ciprofloxacin, ofloxacin, levofloxacin) are currently the drugs of choice, although there are reports from India, Nepal, and Vietnam of quinolone resistance. Oral administration of a quinolone results in (1) very high fecal drug concentrations; (2) rapid control of diarrhea and elimination of Salmonella from stool; (3) reductions in rate of relapse and carrier rates; and (4) prevention of blood stream infection (bacteremia) and other complications. A distinct advantage of the quinolones in uncomplicated typhoid is their efficacy with treatment courses as short as 3 days. Cure rates with ofloxacin given for 3 days (15 mg/kg daily) have been as high as 96% to 100%, but most experts, because of the increase in drug resistance, now recommend a full 10- to 14-day course of treatment to reduce relapses. The longer course of treatment is recommended primarily for travelers who acquire the illness in Asia or Southeast Asia.

Cephalosporins Third-generation cephalosporins (for example, ceftriaxone) are also effective, but patients may remain ill for more than 1 week, whereas the average time to fever clearance with the quinolones is about 4 days. Another advantage: The quinolones can be self administered by a traveler, whereas most cephalosporins must be given by intravenous or intramuscular injection.

Fluoroquinolones The fluroquinolones are very effective in children with multidrug-resistant typhoid fever or other systemic salmonelloses. Quinolones, however, should not be used to treat Salmonella meningitis; a third-generation cephalosporin is preferred.

Azithromycin Azithromycin (Zithromax) is also an effective drug. One thousand milligrams (1,000 mg) taken on the first day, followed by 500 mg daily for 6 additional days, was 100% effective in one study. In children, a dose of 10 mg/kg/day for 7 days was more than 90% effective with few adverse effects.

Summary: Both ciprofloxacin and azithromycin are shown here to be equally effective in treating uncomplicated multidrug-resistant typhoid fever.

Prevention

Human carriers transmit Salmonella typhi bacteria, and in all countries where there is substandard sanitation there is the risk of typhoid transmission. Pay close attention to dietary safety. Especially avoid raw vegetables and salads because these items are often grown in contaminated irrigation water. All food should be well cooked. You should drink only commercially bottled, boiled, or treated water, or commercial beverages. Flavored ices sold by street vendors are especially risky.

Vaccination See Chapter 3 for typhoid vaccine schedules, indications, precautions, and contraindications. Currently available vaccines are about 70% effective. Travelers, therefore, can still acquire typhoid, or paratyphoid (a similar illness), if exposed to a heavy dose of bacteria, or if the vaccine had not been properly administered or handled, as can happen with the oral vaccine. In 1994, eight Dutch travelers in a tour group to Indonesia were diagnosed with typhoid fever, despite having received the oral Typhim 21a vaccine. Therefore, dietary discretion remains an important factor in disease prevention. Don't rely entirely on the vaccine for protection.

Salmonella Enteritis (Salmonellosis)

Other species of salmonella bacteria (Salmonella enteritidis, Salmonella cholerae-suis) cause primarily diarrhea, an intestinal illness termed salmonella enteritis. Typical symptoms include fever, nausea, vomiting, abdominal cramps, and diarrhea. Occasionally, salmonella bacteria enter the blood stream and cause a severe, life-threatening illness termed salmonella bacteremia, characterized by chills, high fever, and prostration. Fatalities from bacteremia occur most often in infants, the elderly, the chronically ill, and those with immune system deficiencies.

Unlike Salmonella typhi bacteria, which are harbored only by humans, other salmonella species are found in a variety of animals including poultry (especially chickens), turkeys, ducks, livestock (pigs, horses, sheep), dogs, cats, rodents, and reptiles (snakes, lizards, turtles). Be aware that purchasing a pet anywhere in the world carries the risk of salmonella infection. Up to 60% of turtles, snakes, iguanas, and lizards in pet stores may harbor bacteria.

Infection is usually transmitted by direct contact with the flesh of an infected animal (e.g., during butchering or food preparation) or by the consumption of undercooked, contaminated food. Undercooked chicken eggs and unpasteurized dairy products are also common sources of illness. Poultry products account for more than one half the cases of salmonellosis.

Treatment

Salmonellosis is best treated with a quinolone antibiotic. A third-generation cephalosporin (ceftriaxone or cefixime) is an alternative drug.

Prevention

There is no vaccine. The typhoid fever vaccine is not effective against the other salmonella bacteria that cause salmonellosis. Prevention is entirely dependent on eating well-cooked food (especially dairy products) and avoiding disease-carrying pets such as turtles and lizards.

Shigellosis (Bacillary Dysentery)

The most common cause of bacterial dysentery is shigellosis, an infection with Shigella species bacteria. This disease accounts for 10% to 40% of diarrhea worldwide. Because very small numbers of bacteria are needed to transmit this disease, the infection can be easily acquired, either from contaminated food or from person-to-person contact with carriers of the bacteria. Flies can also carry and transmit shigella.

Bacillary dysentery is characterized by an abrupt onset of high fever, abdominal cramps, small-volume bloody diarrhea, and the repeated feeling of incomplete bowel evacuation. Voluminous, watery diarrhea may precede the onset of bloody diarrhea. In contrast, amebic dysentery manifests with a gradual onset of diarrhea, associated with low-grade fever. Fulminating colitis with shigellosis is uncommon.

Although a stool culture is needed for exact diagnosis, shigellosis should be suspected on the basis of the symptoms. Other bacteria that can cause similar symptoms include Campylobacter, Salmonella, Vibrio parahaemolyticus, Yersinia, and enteroinvasive E. coli. Because these microorganisms, like Shigella, can all be treated with a quinolone antibiotic, it is not necessary to know the exact bacterial diagnosis before starting treatment.

Treatment

Because bacterial resistance to tetracycline, trimethoprim/sulfamethoxazole, and furazolidone has increased worldwide, shigellosis is best treated with a quinolone antibiotic. The oral cephalosporins do not appear to be effective. If your initial symptoms are severe with high fever and dehydration, hospitalization may be necessary. One species of Shigella (Shigella dysenteriae) is often more resistant to antibiotics and causes more severe illness and 5 to 10 days of quinolone treatment are usually required.

Azithromycin (Zithromax) is also an effective drug. Take 500 mg on the first day, then 250 mg for an additional 4 to 5 days. The cure rate is approximately 80%, which is similar to the quinolones. (The cure rate with ciprofloxacin is about 90%.)

Brucellosis

This is a bacterial disease contracted through (1) the consumption of contaminated dairy products, particularly unpasteurized soft cheeses and milk, (2) by exposure to the flesh of infected animals, particularly that of cattle, hogs, or goats, and (3) by aerosols. In this regard, farmers, herdsmen, veterinarians, and slaughterhouse workers are at particular risk.

Worldwide, most cases of brucellosis occur occur in the Mediterranean basin, notably Greece, France, and Spain, the Middle East, Mexico and Central/South America and India. Brucellosis should be suspected in travelers who have visited these areas and later develop a prolonged illness with fever.

About 100 cases are diagnosed annually in the U.S., and many of these cases are due to drinking unpasteurized goat milk, often brought in from Mexico.

The brucella bacteria may incubate in the body for a month or more before causing symptoms, and the diagnosis, initially, may not be suspected. The most common symptoms include fever, chills, sweating, muscle and joint aches, abdominal pain, weakness, weight loss, and headache. Backache and testicular pain are not uncommon. In contrast to the large number of symptoms, physical findings are infrequent. The physical examination most often demonstrates enlargement of the spleen, liver and lymph nodes. Joint swelling may occur. Heart valve infection (endocarditis) is rare, but accounts for most fatalities. Other diseases that mimic brucellosis include typhoid, mononucleosis, leishmaniasis, and tuberculosis. Early diagnosis of brucellosis depends on a high degree of suspicion for the illness; knowing the travel history and possible exposure to the disease is very important. A positive serology test and positive blood or bone marrow cultures confirm the diagnosis.

  • Antibody testing is the most reliable method for diagnosing brucellosis.
  • The best test is the tube agglutination method, which tests for anti-O-polysaccharide antibody. Titers of 1:160 or higher are diagnostic.
  • Enzyme-linked immunosorbent assay (ELISA) methods lack standardization.

Treatment Brucellosis bacteria often persist inside white blood cells despite antibiotics. Treatment with two antibiotics for at least 6 weeks is required.

  • Doxycycline, 100 mg twice daily x 3-6 weeks
  • Rifampin 600 to 900 mg daily x 3-6 weeks

Alternatively, to prevent relapses:

  • Doxycycline, 100 mg orall dail x 3 to 6 weeks, plus
  • Streptomycin, 1 g IV once or twice daily x 2 weeks, or gentamicin, 5.1 mg/kg IV once daily

Prescribe trimethoprim-sulfamethoxazole combined with gentamicin or streptomycin intravenously or rifampin orally for four to 6 weeks in patients younger than 8 years old.

Prevention The destruction of infected dairy animals, immunization of susceptible animals, and pasteurization of milk and milk products can prevent brucellosis. Travelers should not consume unpasteurized milk and other dairy products and should avoid contact with animal carcasses in risk countries.

Leptospirosis

Leptospirosis is the most common zoonosis in the world. (A zoonosis is any disease that humans may acquire from animals.) Distribution is worldwide (except in polar regions), but the disease is most prevalent in the tropics. The causative spirochete Leptospira interrogans is transmitted by contact with contaminated fresh water or moist soil, including jungle swamps and mud. (Contamination is usually from the urine of infected animals, such as rats, mice, pigs, cattle, and dogs.) Contact with the tissue of infected animals can also spread disease. Leptospires enter through cuts or abrasions on the skin or exposed mucous membranes (nose, mouth, eyes). Traditionally recognized as an occupational disease (e.g., farmers, sewage workers, butchers) leptospirosis is becoming more frequently associated with recreational exposure (e.g., hiking, swimming, rafting) and following heavy flooding; major outbreaks have recently occurred among eco-challenge racers in Costa Rica and Borneo, in Nicaragua, Honduras, and Guatemala following heavy flooding. Recreational and wilderness travelers to the tropics should be aware of the risk for infection.

Many cases are asymptomatic or mild. More severe cases manifest with high fever, headache, conjunctival suffusion (eye redness and edema without secretions), severe muscle pain (myalgia), and stiff neck (from aseptic meningitis). Weil disease, the most severe and sometimes fatal form of leptospirosis, is associated with liver dysfunction and jaundice, but death is almost always the result of kidney (renal) failure, not liver failure. Other findings in severe leptospirosis include bleeding from hemorrhagic coagulopathy and capillary damage, marked leukocytosis, and hemorrhagic pneumonitis. Differential diagnosis includes hepatitis, malaria, typhoid fever, dengue fever, scrub typhus, and hemorrhagic fever with renal syndrome.

Treatment and Prevention

The incubation period is usually 7 to 14 days (range 2 to 21 days). You should seek prompt medical advice if symptoms suggestive of leptospirosis develop within the incubation period after freshwater exposure.

Effective antibiotics include penicillin, amoxicillin, erythromycin, doxycycline, and ceftriaxone. Dialysis is indicated for acute renal failure. Prevention consists of avoiding potentially contaminated fresh water (rivers, lakes, streams) and soil. Drinking water should be filtered, boiled, or treated with iodine. Chemoprophylaxis with doxycycline, 200 mg weekly, is effective and safe for short-term, high-risk exposure.

Meningococcal Meningitis

This illness is caused by bacteria (Neisseria meningitidis) that infect the membranes lining the brain and spinal cord. Unless treated immediately, meningococcal meningitis can be rapidly fatal.

The Neisseria bacteria are normally carried harmlessly in the nasal passages of a small percentage of healthy people. This carriage of bacteria tends to be seasonal and increases during the dry season. Coughing and sneezing spread the bacteria person-to-person. Crowded living conditions increase the number of carriers and the transmission of disease. Travelers are usually exposed to infection only through close contact with the local population in endemic areas. It is not entirely clear, however, what triggers the infection in people carrying the bacteria. In some cases, it may be that an upper respiratory infection has damaged the immune defenses of the mucous membranes of their nose and throat; climatic conditions, as well as temperature and humidity, may also play roles.

Disease is caused by one of five bacterial serogroups: A, B, C, Y, and W-135. Group A is the most common cause of epidemics in the world, particularly in the African “meningitis belt.” W-135 has emerged as a significant cause in Africa and the Middle East, particularly among pilgrims during the Hajj and Umra in Saudi Arabia. Group B is responsible for most outbreaks in industrialized countries. In the United States, groups B, C, and Y each account for about one-third of cases. Group C causes many cluster outbreaks among college students and military recruits.

Distribution of Meningitis, Central Africa from CDC, Yellow Book

Symptoms and Treatment

Fever, vomiting, headache, neck pain and stiffness, and confusion or lethargy are the most common symptoms, but early illness can also mimic “the flu.” Neck and back pain and stiffness are the hallmarks of any form of meningitis but are not necessarily present. Effective antibiotics for treating meningococcal meningitis include ceftriaxone (Rocephin) and cefotaxime (Claforan). Vancomycin is usually added while cultures are pending. Chloramphenicol can be used in penicillin-allergic patients, although resistant strains have been reported. Quinolones also appear to be effective. Patients treated with penicillin G may take longer to recover because of the occurrence of relatively resistant strains of N. meningitidis.

Prevention

Don't Smoke Cigarette smoking damages the mucous membranes of the airway and has been shown to be a risk factor for contracting meningitis.

Vaccination The quadrivalent polysaccharide vaccine Menomune (Aventis Pasteur) is protective for 3 years against serogroups A, C, Y, and W-135. In January 2005, the U.S. Food and Drug Administration licensed Menactra (Aventis Pasteur), a quadrivalent vaccine which appears to be more effective against the same four serogroups. Menactra is a conjugate vaccine that protects for 8 years; it also reduces nasal carriage of Neisseria bacteria, which limits disease spread during outbreaks. Menactra was developed primarily to prevent meningitis in adolescents, especially college students living in dormitories, but it is likely to become the preferred vaccine for travelers, even those outside the 2- to 55-year age range for which it is approved.

Vaccination is recommended for travelers going to meningitis-belt countries in sub-Saharan Africa during the dry season, November through June, if they will have have close contact with the local population - and for any traveler going anytime into an epidemic area. Travelers at higher risk include those visiting friends and relatives, adventure travelers, health-care workers, missionaries, and volunteer or relief workers. Those who travel on a tourist itinerary, have limited contact with the local population, and stay in tourist accommodations probably don't need to be vaccinated.

Meningococcal vaccine is usually not given to children younger than 2 years of age but under special circumstances may be administered to infants as young as 3 months of age. NOTE: The conjugate vaccine (Menactra) is more immunogenic and probably more effective in infants and young children. The CDC no longer recommends meningococcal vaccine for travel to Nepal, India, Mongolia, Kenya, Burundi, or Tanzania. Vaccination, however, is required for entry into Saudi Arabia for those embarking on the annual Hajj pilgrimage to Mecca.

The occurrence of meningitis outbreaks worldwide can be checked on the CDC website at http://wwwn.cdc.gov/travel.

Influenza

The risk for exposure to influenza during international travel depends on the time of year and destination. In the tropics, influenza can occur throughout the year, while in the temperate regions of the Southern Hemisphere most activity occurs from April through September.

Influenza virus infections cause disease in all age groups. Rates of infection are highest among infants, children, and adolescents, but rates of serious illness and fatalities are highest among persons older than 65 years of age and persons of any age who have chronic medical conditions.

Prevention The influenza vaccine must be administered yearly to optimize protection because vaccine-derived immunity declines over time and because the vaccine strains are updated annually to reflect ongoing antigenic changes among circulating influenza viruses. Influenza vaccine should be recommended before travel for persons at high risk for complications of influenza if:

  • Influenza vaccine was not received during the preceding fall or winter

  • Travel is planned to the tropics

  • Travel is planned with large groups of tourists at any time of year

  • Travel is planned to the Southern Hemisphere from April through September

In North America, travel-related influenza vaccination should take place by spring when possible, because influenza vaccine may not be available during the summer. Travelers at high risk for influenza-related complications who plan summer travel should consult with their physicians to discuss the symptoms and risks of influenza before embarking (Source: CDC).

Two types of influenza vaccine are currently available for use in the United States:

Pregnant women, children >6 months of age, and all other travelers (not just high-risk travelers) should also consider "getting a flu shot" with the inactivated vaccine (or FluMist®, if appropriate) prior to international travel if they have not been immunized during the previous 12 months.

Avian Influenza A ("Bird Flu")

Avian influenza A (H5N1) is predominantly a disease of birds. The virus does not pass easily from birds to people and does not to pass from person to person (except in very rare cases of close contact with an infected blood relative). The risk to humans from avian influenza is believed to be very low and no travel restrictions are advised, except travelers should avoid visiting animal markets, poultry farms and other places where they may come into close contact with live or dead poultry, or domestic, caged or wild birds and their excretions. In addition, travelers are advised to:

  • Cook poultry and egg dishes thoroughly. (Well-cooked poultry is safe to eat.)

  • Wash hands frequently with soap and water if around poultry.

The World Health Organization (WHO) does not recommend travel restrictions to countries experiencing outbreaks of influenza A (H5N1) in birds, including those countries which have reported associated cases of human infection.

  • To date, no cases of avian influenza A (H5N1) illness have been identified among short-term travelers visiting countries affected by outbreaks among poultry or wild birds.

The usual vaccines against influenza are not protective against bird flu. Oseltamivir (Tamiflu) is somewhat effective in the treatment of avian influenza A (H5N1). It seems to be effective in some cases, but may fail in others. Recently, resistant strains have been reported. In addition, the dosage and duration of treatment appear to be different in severe cases.

Tuberculosis (TB)

Tuberculosis has afflicted the humans since the beginning of recorded history and today is the second leading cause of death from communicable disease. TB and HIV/AIDS co-infection leads to substantial morbidity and mortality. Sub-Saharan Africa has the highest incidence per capita (350 cases per 100,000), but the most number of cases occurs in the South and South East Asia, with the majority of cases in Bangladesh, India, Indonesia, Myanmar and Thailand.

Tuberculosis (TB) is transmitted following inhalation of infectious respiratory droplets. Most travelers are at low risk. Travelers at higher risk include those who are visiting friends and relatives (particularly young children) in high-endemic countries, long-term travelers, and those who have close contact, prolonged contact with the local population. There is no prophylactic drug to prevent TB*. For travelers with significant exposure, pre- and post-travel tuberculin skin testing may be considered, either as a screening test for latent or recent infection or as an aid to diagnosis of active disease. A blood test that detects the presence of TB bacteria has been approved by the Food and Drug Administration. Called QuantiFERON®-TB Gold In-Tube (QFT™), it has the advantage of eliminating the common false-positive results of the tuberculin skin test (PPD).

*A tuberculosis vaccine, BCG, is administered to young children in the UK, but is not available (nor recommended) in the U.S. or Canada.

There has been concern about transmission of TB aboard airliners, specially during long-haul flights. The Centers for Disease Control and Prevention (CDC) studied six separate incidents of airplane travel by a person subsequently found to be suffering from TB. The CDC and WHO have concluded that the risk of TB transmission on an aircraft does not appear to be greater than in other confined spaces.

Extensively drug-resistant tuberculosis (XDR-TB) Extensively drug-resistant tuberculosis (XDR TB) is a relatively rare type of multidrug-resistant tuberculosis (MDR TB). It is resistant to almost all drugs used to treat TB, including the two best first-line drugs: isoniazid and rifampin. XDR TB is also resistant to the best second-line medications: fluoroquinolones and at least one of three injectable drugs (i.e., amikacin, kanamycin, or capreomycin).

The condition remains treatable with other types of medications, but those are less effective, costlier and toxic. If the afflicted persons cannot be soon diagnosed and given proper treatment, they can die within a month.

A large part of the drug-resistant TB caseload in Europe occurs in the countries of the former Soviet Union. (By June 2008, 18 countries in the European Union (EU) and Western Europe - and six in the former Soviet Union have officially reported XDR-TB cases.) In South Africa half the XDR cases in patients with HIV infection were acquired in hospitals or clinics, and several occurred in health care workers. Mortality exceeded 95%.

Schistosomiasis (BILHARZIA)

Schistosomiasis (also called bilharzia) is a parasitic disease caused by schistosomes, or blood flukes. The disease affects more than 200 million people worldwide. The disease is endemic in Africa (most countries), South America (Brazil, Venezuela, Suriname), and parts of the Middle East and Asia. In the Caribbean, schistosomiasis has been reported to occur sporadically in Puerto Rico, Antigua, Dominica, Guadeloupe, Martinique, Montserrat, and Saint Lucia.

The three most common schistosome species are Schistosoma mansoni (the cause of intestinal schistosomiasis), Schistosoma hematobium (the cause of urinary schistosomiasis), and Schistosoma japonicum (Far Eastern schistosomiasis). Other species, such as Schistosoma mekongi, found in Southeast Asia, and Schistosoma intercalatum, found in Africa, are less common. Infection takes place when schistosome cercariae (larvae), shed into fresh water by snail-intermediate hosts, penetrate the unbroken skin of an individual who is washing, bathing, wading or swimming in ponds, lakes, or slow moving rivers, streams, or irrigation ditches in endemic areas. After skin penetration, there follows a 4- to 6-week incubation period during which time the young schistosome worms migrate through the lungs to the liver and to the veins draining the intestine or the bladder. The fully grown worms live in the veins of the urinary bladder or the wall of the intestine where they produce large numbers of eggs; it is the eggs that cause inflammation and progressive tissue damage. The adult worms can persist for decades, producing various, often puzzling, symptoms.

Light infections are usually asymptomatic. When schistosome larvae penetrate the skin, there may be brief tingling and a rash, called swimmer's itch. If you are exposed, you should towel off vigorously and wash your skin with rubbing alcohol. This may prevent penetration of the cercariae. Corticosteroid creams and antihistamines can help control symptoms.

Worldwide Distribution of Schistosomiasis from CDC Yellow Book

More detailed maps on the geographical distribution of schistosomiasis here.

Acute schistosomiasis (Katayama fever) may occur a few weeks to months after exposure, This disease is typically seen in tourists, who are unlikely to have had previous exposure. Symptoms include high fever, muscle aches, lethargy, dry cough, and a rash (hives). These symptoms are believed to represent an allergic (hypersensitivity) reaction to the migrating worms. Katayama fever can be confused with malaria or typhoid fever but More detailed maps on the worldwide distribution of schistosomiasis here.the blood count will show marked eosinophilia and a chest X-ray may show patchy infiltrates. Note: Many persons will not develop Katayama fever during the acute infection—they may experience just a feeling of fatigue or ill health. Most patients recover in 2 ro 10 weeks, but in some the illness progresses to more serious disease with weight loss, diarrhea, widespread rash, diffuse abdominal pain, and enlargement of the liver and spleen.

Central Nervous System (CNS) Schistosomiasis Rarely, migrating eggs or adult worms can invade the central nervous system. Symptoms of cerebral schistosomiasis include headaches, visual loss, and seizures, if the infection is in the brain. Symptoms of spinal cord schistosomiasis include urinary incontinence, leg pain, and paralysis.

Chronic Schistosomiasis Heavy infections (seen mainly in the indigenous populations) can last for years and can damage the liver, bladder, bowel, and/or nervous system. S. mansoni, S. japonicum, and S. mekongi parasites primarily affect the bowel and liver; chronic infections can lead to enlargements of the liver and spleen, followed by scarring of the liver and gastrointestinal bleeding from dilated esophageal veins. Bowel involvement may lead to chronic diarrhea and abdominal pain, suggestive of inflammatory bowel disease. S. hematobium primarily affects the genitourinary tract. Chronic infections can lead to persistent cystitis, frequency of urination, blood in the urine, obstructive kidney disease, and an increased incidence of bladder cancer; most travelers, however, with schistosomiasis are asymptomatic. Symptoms usually occur only when there is a heavy worm burden as a result of repeated or prolonged exposure to infested fresh water.

One of the most important elements in diagnosing schistosomiasis is obtaining a history of freshwater exposure in an endemic area. A white blood cell count may show eosinophilia, but this finding is not specific for schistosomiasis. (About 20% to 30% of patients will have eosinophilia.) The standard diagnostic test is an examination of stool and urine for schistosome eggs. In some cases, a rectal or bladder biopsy will demonstrate eggs; schistosome eggs, however, do not appear for at least 40 days following the initial exposure. In suspected schistosomiasis, a highly accurate serology antibody test using an enzyme-linked immunosorbent assay (ELISA) will usually be diagnostic 6 weeks or more after exposure. This test is far more sensitive than stool or urine examination. The CDC's Parasitic Disease Branch (404-488-4050) can provide information about the ELISA assay. A positive test indicates present or past infection, but does not distinguish between the two.

Schistosomiasis of the nervous system, which is extremely rare, causes varying neurological symptoms. The blood eosinophil count may be normal, and the stool and urine egg examination may be negative. Diagnosis is made with the ELISA assay combined with an MRI examination of the central nervous system.

Treatment

For S. mansoni and S. hematobium, praziquantel is curative in a single dose of 40 mg/kg. For the treatment of S. japonicum and S. mekongi, praziquantel, 60 mg/kg, is given in three divided doses 6 hours apart. Retreatment may be indicated 6–12 weeks later to cure prepatent infections, particularly if eosinophilia, high antibody titers, or symptoms persist.

Prevention

There is no vaccine; therefore, avoiding contact with infested water is the most important preventive measure. Do not swim in slow-moving fresh water unless a reliable source assures you that it is safe. (Chlorinated swimming pools and seawater are safe.) Water for bathing is considered safe if it has been heated to above 50° C (122° F) for more than 5 minutes, if it has stood for more than 48 hours in a tub or container, or if it has been chemically treated (e.g., chlorinated) as for drinking water. If you cannot avoid freshwater exposure, swim or bathe in a rapidly flowing river or stream and stay away from the shoreline of a lake. Researchers have suggested that applying controlled-release DEET may prevent skin penetration by the larvae, but data are preliminary.

Liver Fluke Diseases

These other flukes, unlike the blood flukes (which cause schistosomiasis), are acquired by eating raw or undercooked fish, shellfish, or raw water vegetables.

Clonorchiasis Infection with Clonorchis sinensis occurs after the consumption of raw, undercooked, pickled, or smoked freshwater fish that contain parasitic larvae. Clonorchiasis is common in Laos, Cambodia, Thailand, southern China, Hong Kong, Korea, Japan, and far eastern Russia. Travelers can avoid this disease by eating only well-cooked fish. Symptoms relate to obstruction of the bile ducts and include abdominal pain and jaundice. Most infected individuals, however, are asymptomatic. Clonorchiasis is treated with praziquantel, 75 mg/kg total in three divided doses in 1 day (25 mg/kg orally three times in 1 day). Albendazole has also been shown to be an effective alternative. Untreated clonorchiasis has been associated with bile duct cancer and gallstones.

Opisthorchiasis This disease is caused by Opisthorchis species of flukes. It is acquired in the same way as clonorchiasis, and the symptoms and treatment are also the same.

Fascioliasis Human infection is quite widespread, occurring in 66 countries in Africa, China, Latin America, and Europe. Fasciola hepatica parasites are acquired by ingesting parasitic larvae attached to aquatic plants, usually watercress. Symptoms include fever, upper abdominal pain, weight loss, and marked elevation of blood eosinophils. Hypodense cystic lesions are frequently found in the liver on imaging studies. Treatment is with triclabendazole, 11 mg/kg in a single dose.

Lung Fluke Disease

Paragonimiasis Humans develop paragonimiasis after consuming raw, salted, or wine-soaked crustacea (freshwater crabs, crayfish, and shrimp). The species Paragonimus westermani is prevalent in parts of China, Korea, Japan, the Philippines, and Taiwan. Other Paragonimus species infect humans in West Africa and Central and South America. Symptoms include coughing up blood and chest pain. It is treated with praziquantel, 75 mg/kg in three divided doses on 2 consecutive days. Triclabendazole has also been shown to be effective. Travelers can avoid lung fluke disease by not eating raw or undercooked freshwater shellfish.

Intestinal Fluke Disease

Fasciolopsiasis Giant intestinal fluke disease is common in the Far East and is acquired through the ingestion of parasitic larvae attached to aquatic plants such as water chestnuts, which have been contaminated by sewage from mammals (pigs, humans). The causative parasite is Fasciolopsis buski. Symptoms of heavy infection include abdominal pain, chronic diarrhea, loss of appetite, and weight loss. Treatment is with praziquantel.


Intestinal Roundworm/NEMATODE Diseases

Angiostrongyliasis The rat lung worm, Angiostrongylus costaricensis, is the cause of abdominal angiostrongyliasis, and its cousin, Angiostrongylus cantonensis, as well as the most common cause of eosinophilic meningitis (inflammation of the spinal cord coverings) in humans. It occurs in Costa Rica and other Central American countries, as well as Southeast Asia, and the Pacific basin and the Caribbean. Human infection occurs through ingestion of larvae present in snails or slugs; or transport hosts, such as freshwater prawns, frogs, or fish; or vegetable produce contaminated by either. The ingested larvae migrate to the mesenteric arteries, causing inflammation resulting in abdominal pain and fever that can mimic appendicitis. Larvae that travel to the brain can cause eosinphilic meningoencephalitis (inflammation of the brain). Treatment is with albendazole and corticosteroids.

Ascariasis This is the most common helminth infection in the world. The roundworm, Ascaris lumbricoides, lives in the intestine and produces eggs that are passed in human feces; eggs then incubate in soil for 2 to 3 months before becoming infective to humans. When these eggs are ingested through fecally contaminated food or water, they enter the intestinal tract and hatch into larvae that penetrate the gut wall and are carried to the lung, coughed up, and swallowed. Then larvae develop into adult worms and produce eggs, and the life cycle is completed.

Symptoms of ascariasis are produced by migration of larvae through lung tissue during early migration and also by the presence of adult worms in the intestinal tract. Symptoms of ascariasis include cough, wheezing, fever, and chest pain. There may be eosinophilic inflammation of lung tissue. Intestinal symptoms from heavy infection include nausea, loss of appetite, and abdominal pain. Migrating worms can cause intestinal perforation, bile duct obstruction, appendicitis, and pancreatitis. In children in the developing world, ascariasis is the most common cause of bowel obstruction. Most infections are asymptomatic. Occasionally, the 8-inch adult worm (it looks like an earthworm) will pass spontaneously in the stool or out the mouth or nose. Treatment with a single 400-mg dose of albendazole cures 100% of infections. Mebendazole, 100 mg twice daily for 3 days, or pyrantel pamoate (Antiminth, Reese's Pinworm), 11 mg/kg in one dose, is also effective.

Hookworm Disease (ancylostomiasis) This disease is acquired by walking barefoot in areas where there is fecal contamination of the soil harboring hookworm larvae. The larvae enter the body by penetrating the unbroken skin of the foot, pass through the lungs, and end up in the intestine, where they develop into adult worms. Symptoms of hookworm disease may include coughing and wheezing, peptic ulcer-like pain, and fatigue from anemia. Most infections are asymptomatic. Treatment with mebendazole, 100 mg twice daily for 3 days, albendazole, 400 mg (single dose), or pyrantel pamoate, 11 mg/kg daily for 3 days, is effective.

Whipworm Disease (trichuriasis) Trichuris trichiura is one of the most prevalent worm (helminth) infections in the world. The adult worms can live up to 7 years in the intestinal tract, producing thousands of eggs that are passed in the stool. Heavy infections can cause abdominal pain, chronic diarrhea, rectal prolapse, and stunting of growth in children. However, most infections are asymptomatic. Treatment with mebendazole, 100 mg twice daily for 3 days, or albendazole, 400 mg daily for 3 days, is recommended. Travelers can prevent infection by eating only cooked food and rinsing vegetables in hot water (65° C [149° F] or above), an iodine solution, or bleach.

Intestinal Capillariasis—This is a serious infection that occurs in the Philippines, in Thailand, and occasionally in other countries in Southeast Asia. The infection is acquired by the ingestion of raw freshwater fish that harbor infective worm larvae. The parasitic worms, Capillaria philippinensis, invade the small intestine and can cause chronic diarrhea, malnutrition, and wasting. The disease may be fatal.

The diagnosis of capillariasis is made by finding characteristic eggs in the stool or by examining tissue obtained from a biopsy of the small intestine. A blood serology (ELISA) test is available in certain research laboratories. Eosinophilia occurs but is a nonspecific finding. Treatment with mebendazole, 200 mg twice daily for 20 days, is curative. Albendazole is also effective. Avoiding raw fish prevents this (rare) infection.

Strongyloidiasis Like hookworm, Strongyloides larvae also enter the body through skin penetration, pass through the lungs, and enter the intestine. In travelers, strongyloidiasis is one of the most important intestinal worms because it is a potentially fatal disease in those whose immune system is compromised by conditions such as cancer, AIDS, radiation therapy, and medication (especially corticosteroids). Symptoms include hives and peptic ulcer-like abdominal pain. Diarrhea and a cough are early symptoms in heavily infected individuals. However, most infected people are asymptomatic. Because this is one of the only worms capable of multiplying in humans, it will often live indefinitely in the body unless it is treated.

Strongyloidiasis and hookworm disease are common causes of undiagnosed eosinophilia in travelers. Strongyloides infection is often missed even after multiple stools have been examined. Serology testing through the CDC is 95% sensitive and should be carried out when the diagnosis is suspected and laboratory examination of the stool are negative. Treatment is with ivermectin, 200 mg/kg daily for 2 days, or albendazole, 400 mg twice daily for 7 days.

Anisakiasis This is a parasitic disease transmitted by eating raw, undercooked, or lightly pickled saltwater fish, especially salmon, herring, mackerel, whitefish, cod, pollock, bonito, and sole. The parasite is the larval form of a marine roundworm, which may be present in the muscles and organs of the fish just mentioned. The worm attaches to the lining of the stomach or intestine. Symptoms include nausea and vomiting, or abdominal pain that mimics appendicitis. All good sushi chefs prepare raw fish so as to virtually eliminate the risk of anisakiasis. Freezing fish also kills the parasite. The treatment is surgical excision of the worm from the intestinal tract.

Intestinal Tapeworm Diseases

Diphyllobothriasis (fish tapeworm disease) This is an infection caused by a fish tapeworm called Diphyllobothrium latum and occurs among people who eat raw, smoked, pickled, or undercooked freshwater fish. These include Eskimos, fishermen, devotees of sushi bars (salmon), and people who taste raw fish (such as whitefish) while cooking. Symptoms are uncommon but may include primarily abdominal cramps and diarrhea, but fatigue and, rarely, anemia from vitamin B12 deficiency can also occur because fish tapeworms consume this important vitamin. Treatment (adults and children) is with a single dose of praziquantel, 10 mg/kg

Taeniasis Infections involving the pork and beef tapeworms are also called taeniasis.

Beef Tapeworm Disease This infection acquired by eating raw or undercooked beef and is caused by the beef tapeworm Taenia saginata. Many infections are asymptomatic. Classically, people with this infection may notice a small worm segment, or longer piece of the worm, passed in their stool during a bowel movement or crawling out of their anus between bowel movements. Symptoms may include nausea and abdominal cramps. Treatment (adults and children) is with a single dose of praziquantel, 10 mg/kg.

Pork Tapeworm Disease This intestinal infection, similar to beef tapeworm disease, is caused by the pork tapeworm Taenia solium and is acquired by eating undercooked pork that contains the encysted larvae of the tapeworm. Treat with single-dose praziquantel, 10 mg/kg.

Cysticercosis This is a more serious infection than pork tapeworm disease because it involves organs outside the intestine. Cysticercosis occurs when a person ingests pork tapeworm eggs (not the larvae), usually by eating fecally contaminated food. The eggs hatch in the intestine and develop into larvae that penetrate the intestinal wall and invade various organs and tissues of the body. The most serious illness that results, neurocysticercosis, occurs when tapeworm larvae invade the brain and form cysts, causing seizures and other neurological symptoms. Cysticercosis is common in Mexico, Central and South America, Africa, India, China, Eastern Europe, and Indonesia. Infection is very rare in travelers but not uncommon in immigrants from developing countries.

Both praziquantel and albendazole are effective drugs for treating cysticercosis, but the latter is preferred (15 mg/kg/day for 10 to 30 days, or up to 400 mg twice daily for 10 to 30 days). The dose of praziquantel is 50 to 75 mg/day for 15 days. Corticosteroids are often prescribed as adjunctive treatment to prevent serious allergic reactions to dying larvae.

Trichinosis This disease (also called trichinellosis) occurs worldwide, except in Australia, and is most often acquired when people eat raw or undercooked pork containing the larval cysts of the parasite Trichinella spiralis. Trichinosis, however, can also be acquired by the ingestion of undercooked meat of other carnivorous animals and wild game such as black bear, polar bear, walrus, wild boar, bush pigs, and wart hogs.

During the first week after ingestion, the larvae in the intestine develop into adult worms, causing abdominal pain, diarrhea, nausea, vomiting, and prostration. Next, there is tissue invasion by newly produced larvae, bringing fever, headache, swelling of the eyelids and face, conjunctivitis, muscle pain, weakness, and hives. Symptoms caused by larval invasion of the heart and central nervous system include heart rhythm disturbances and seizures.

Treatment with prednisone (60 mg/day) is used in acute trichinosis to reduce inflammation and alleviate symptoms. Albendazole, 400 mg twice daily for 14 days, is the treatment of choice. An alternative treatment is mebendazole, 400 mg, three times daily for 4 days, then 400 to 500 mg/day for 10 days. Adequate cooking will prevent this infection. Freezing, smoking, or pickling is as effective.

Rabies

Rabies is one of the most ancient and feared diseases. It is estimated that as many as 50,000 people worldwide die each year from rabies, mostly in the developing countries of Africa, Asia, and Latin America. Travelers to these countries (especially those visiting small villages and rural areas) need to assess their potential risk of exposure, especially to dogs, which transmit most cases of human rabies in less developed countries.

The highest risk of rabies occurs in El Salvador, Guatemala, Mexico, Colombia, Ecuador, Peru, Nepal, India, Pakistan, Bangladesh, Sri Lanka, Thailand, Vietnam, and the Philippines. More than 50 countries reportedly have no rabies cases.*

All mammals are susceptible to rabies and can transmit the virus, but true reservoirs, which maintain the virus in nature, persist only among carnivorous mammals and bats. Unvaccinated domestic animals and humans can become rabid after exposure to such reservoirs. Infected livestock will die of the disease before transmitting it; cats (usually infected by dogs or wild animals) can transmit the disease, but are not reservoirs of infection.

In North America, raccoons, skunks, bats, and foxes are the primary reservoirs capable of transmitting infection. Because most dogs are now vaccinated, fewer than 100 rabid dogs were reported in the United States in 2002. In fact, more cases of cat rabies were reported, because these animals are less supervised and are vaccinated less often. The mongoose is an important vector in Puerto Rico, the fox in Europe, the jackal in much of Africa, the wolf in Iran and neighboring countries, and the vampire bat in certain Latin American countries. Therefore, at the very least, travelers should not approach or pet stray dogs, cats, monkeys, or feral animals.

Pre-Exposure Vaccination Adventure travelers and long-term expatriates often underestimate the risk of rabies. If you plan to stay for more than 30 days in a country where rabies is a constant threat, especially if you travel to remote areas, you should strongly consider pre-departure rabies vaccination. The advantages to pre-departure vaccination include the following:

  • You won't need to receive rabies immune globulin (RIG), which is often not available in developing countries, and is very expensive.
  • You will need only 2, not 5, doses of rabies vaccine after exposure. Although three pre-exposure doses of vaccine provide lifetime protection, postexposure booster doses are always required.
  • A delay in treatment will be less critical because you already have some immunity. If rabies vaccine is not locally available you will need to travel to where the vaccine is available, but there is a bit less urgency.

There are three equally effective rabies vaccines commercially available in the United States: (1) Imovax (human diploid cell vaccine-HDCV); (2) RabAvert (purified chick embryo cell culture-PCEC); and (3) Rabies Vaccine Adsorbed (RVA from fetal rhesus lung cells).

Pre-Exposure Vaccination Schedule Rabies vaccine is given as three doses on days 0, 7, and either 21 or 28. RabAvert and RVA should be injected into the deltoid or quadricep (anterior thigh) muscle. The gluteal region should be avoided. Imovax can be administered intramuscularly (IM) or intradermally (ID). Note: Intradermal rabies vaccination must be completed before starting chloroquine or mefloquine. If this is not feasible, then the vaccine must be given IM.

Accelerated Schedule Two doses, 1 week apart (intramuscular route only) when time does not allow three doses to be administered over 21 to 28 days.

Post-Exposure Treatment Following exposure to an animal known or suspected of being rabid, the most important first step is to clean the bite site thoroughly with soap and water or an antiseptic solution. Unvaccinated individuals should receive rabies immune globulin (RIG) and rabies vaccine. People already vaccinated should receive rabies vaccine only. Note: Exposure consists of a bite or a scratch, or the licking of a minor wound or abrasion, by the animal. Coming into contact with a bat, even without an observed bite, may constitute exposure. The rabies virus is contained in the saliva and certain body tissues (e.g., the brain and spinal fluid) of the infected animal. Therefore, contact with the blood, urine, or feces of the animal does not constitute exposure and does not require vaccination.

If you completed a pre-departure rabies vaccination series, you will need two additional doses of intramuscular vaccine (given on days 0 and 3). If not vaccinated, you must receive RIG followed by five doses of rabies vaccine (given on days 0, 3, 7, 14, and 28). Treatment is best started within the first 24 hours after exposure. If anatomically feasible, the entire calculated dose of rabies immune globulin (either human or equine) should be injected directly into the bite(s) and the tissue around the bite(s). If there are large or multiple bites, RIG can be diluted with normal saline if more volume is needed to infiltrate all wound areas. If it is not anatomically feasible to inject the entire volume of RIG into the wound(s), any remaining volume should be injected intramuscularly at a remote site, usually into the deltoid or anterolateral thigh muscles. Note: Injecting into the gluteus muscle risks injury to the sciatic nerve. There is also a greater chance of depositing the injection into fat tissue, resulting in less absorption. RIG dosage: 20 IU/kg (human RIG) or 40 IU/kg (equine RIG). Note: Theoretically, chloroquine may interfere with the immune response, and this drug should be discontinued during post-exposure rabies prophylaxis. The patient, of course, should be monitored for malaria symptoms if chloroquine has been discontinued.

Treatment failures can occur, but these failures are usually preventable and caused by (1) bite wounds not having been immediately and thoroughly cleaned with soap and water; (2) delayed (over 24 hours) treatment; (3) RIG not given with the vaccine; or (4) RIG not infiltrated directly into and around the wound(s). The wounds with the highest risk involve bites of the head, neck, and hands. Note: Prophylaxis should be initiated whenever exposure occurs or is strongly suspected, regardless of the time interval. The incubation period of rabies is 1 to 3 months, but cases have occurred within 2 weeks of exposure, and as long as 1 year later.

Vaccines Overseas In less developed countries, the vaccines used in the United States and Canada are often not available. The same is true for human rabies immune globulin (Imogam, BayRab), also a very expensive product. In the event of rabies exposure abroad, you would likely be given a Vero cell vaccine, a chick cell-derived vaccine, or a purified duck embryo-derived vaccine. These products are effective and safe and have few side effects. Instead of human RIG, you might get purified equine RIG, which has the potential to cause significant side effects unless the newer preparations (from Europe) are used. If you return to the United States or Canada after starting postexposure treatment abroad, the vaccination schedule can be completed using intramuscular Imovax (HDCV), RabAvert (PCEC), or RVA. In many developing countries, neural-tissue vaccines (Semple, Fermi, suckling mouse) are still in common use. These vaccines are cheap but are less effective and potentially very dangerous. They should be avoided, if possible. In the event of a possible rabies exposure, contact the nearest U.S. or Canadian embassy to obtain the location of the nearest reliable medical facility. You should be prepared to evacuate to another country for appropriate medical care (with rabies immune globulin and tissue culture vaccines) if necessary. However, if you begin treatment overseas with a neural-tissue (Semple, Fermi, suckling mouse brain) vaccine, you should try, as soon as possible, to get to a facility (even if it means returning to Europe or North America) that can re-initiate vaccination with one of the newer cell-culture vaccines.

Seafood Toxins

Poisonous toxins in seafood can be an important and often overlooked cause of illness in travelers. Unfortunately, the toxins are often difficult or impossible to detect because they do not usually affect the appearance, smell, or taste of the fish or shellfish. In addition, freezing, drying, smoking, or cooking does not usually destroy them.

Fish Poisoning

Scombroid Poisoning This occurs after eating fish that has been inadequately chilled after capture. It occurs most commonly in tuna and related species and also in mahi-mahi. Affected fish contains histamine and may have a sharp, bitter, or peppery taste. Often, however, the fish looks, smells, and tastes normal. Symptoms of scombroid poisoning resemble an allergic reaction and include flushing, headache, nausea, vomiting, abdominal cramps, and diarrhea. In addition, there may be hives and wheezing. Treatment with antihistamines is very effective.

Ciguatera Poisoning This occurs after eating coral reef fish containing potent toxins that originate in algae found in coral reefs, especially after storms, which may cause an increase in algae. The toxin is passed up the food chain through herbivorous fish to carnivorous fish and eventually to humans. Any part of the fish may contain toxins but the highest concentrations are found in the head, gut, roe, and liver. Almost any reef fish can cause ciguatera poisoning, but it is most common in barracuda, moray eel, grouper, snapper, jack, and sea bass. Large carnivorous fish weighing more than 6 pounds are the most dangerous. Symptoms include diarrhea, nausea, vomiting, and abdominal cramps followed by neurological symptoms such as numbness and tingling involving the arms and legs and the area around the mouth. There may be temperature reversal where cold objects feel hot. For example, ice cream may cause a burning sensation in the mouth. Another bizarre symptom is that the teeth often feel numb or loose. In addition, there may be muscle aches, fatigue, itchiness of the skin, and depression. Some of the symptoms may last weeks or several months. After an episode, travelers should avoid, for several months, alcohol, fish of any kind, and nuts. These substances may exacerbate symptoms. Treatment is directed to relieving the symptoms, but mannitol, given intravenously within 72 hours of onset, may occasionally produce a dramatic improvement. A commercial test (Cigna-check, Oceanit Test) has recently become available to test fish for ciguatoxin (http://www.cigua.com). This test is very sensitive and easy to perform, but it is relatively expensive and probably of limited value for travelers.

Pufferfish or Fugu Poisoning This occurs after eating pufferfish (a bad idea) and less commonly porcupine fish or ocean sunfish, which contain a highly potent toxin known as tetrodotoxin. It is 50 times more potent than strychnine and is usually concentrated in the ovaries, liver, gut, and skin of affected fish. Most cases of pufferfish poisoning occur in Japan where pufferfish or fugu is eaten as a very expensive and prized delicacy. The fugu experience is a feeling of euphoria and exhilaration and is the result of ingesting minute amounts of toxin. Unfortunately, larger quantities of toxins can be rapidly fatal. Symptoms of poisoning include nausea, sweating, dizziness, and neurological symptoms such as numbness, tingling, and weakness. In severe cases, there is widespread paralysis often involving the respiratory muscles. Mortality rates of up to 60% have been reported. Unfortunately, there is no specific antidote, and treatment is directed at relieving the symptoms and providing supportive care.

Shellfish Poisoning

There are two important types of shellfish: crustaceans (e.g., crabs, shrimp, and lobster) and bivalve mollusks (e.g., oysters, mussels, clams, and scallops). Most cases of toxic shellfish poisoning occur after eating bivalve mollusks. The toxins originate in algae, and outbreaks of shellfish poisoning are particularly common after algal blooms or “red tides.” There is no specific treatment or effective antidote for any of the shellfish poisonings, and treatment is directed at relieving symptoms and providing supportive care.

Paralytic Shellfish Poisoning This is the most common and most serious form of shellfish poisoning. Typical symptoms include numbness, tingling, and a sensation of floating. In severe cases, there may be paralysis of respiratory muscles. Deaths are most common in children, and mortality rates of over 40% have been reported.

Neurotoxic Shellfish Poisoning This causes nausea, vomiting, diarrhea, and neurological symptoms such as numbness, tingling, weakness, and dizziness. When the aerosolized toxin is breathed in rough surf, coughing, wheezing, and eye irritation may occur in exposed individuals.

Diarrheic Shellfish Poisoning This causes gastroenteritis with symptoms such as diarrhea, nausea, vomiting, abdominal cramps, weakness, and chills. No deaths have been reported.

Amnesic Shellfish Poisoning This is rare but can cause gastroenteritis and neurological features such as headaches, memory loss, seizures, and long-term dementia. It may be fatal in elderly patients.

Guidelines for the Prevention of Seafood Poisoning

  • Avoid fish that has not been promptly chilled after capture (risk of scombroid).
  • Avoid fish that has an ammonia smell or sharp, peppery taste (risk of scombroid).
  • Avoid reef fish, especially large carnivorous fish such as barracuda, moray eel, grouper, snapper, jack, and sea bass (risk of ciguatera).
  • The maxim is: “Eat no carnivorous fish larger than your plate.”
  • Never eat shellfish associated with algal blooms or “red tides.”
  • Avoid consumption of bivalve mollusks (oysters, clams, scallops, and mussels) in developing countries.
  • Some researchers suggest that ciguatoxin-laden fish can be detected by rubbing a piece of the fish along the gums (before ingestion) to see if a tingling feeling occurs.