Chapter 3Infectious Diseases Related To Travel
Sharon L. Roy
Amebiasis is caused by the protozoan parasite Entamoeba histolytica.
MODE OF TRANSMISSION
Transmission occurs via the fecal-oral route, either directly by person-to-person contact (such as by diaper-changing or sexual practices) or indirectly by eating or drinking fecally contaminated food or water.
Amebiasis occurs worldwide, particularly in the tropics, and is more common in areas of poor sanitation where barriers between human feces and food and water (including ice) are inadequate. From 1996 through 2005, 14 per 1,000 returned travelers seeking medical care at GeoSentinel-associated medical centers around the world were diagnosed with E. histolytica. Amebiasis was most commonly diagnosed in travelers returning from South Asia, South America, and the Middle East, although travelers returning from all regions were affected. Rates were highest among missionaries and volunteers, although tourists, business travelers, travelers visiting friends and relatives, and people traveling for education or research were also diagnosed with the disease. Long-term travelers (duration >6 months) were significantly more likely than short-term travelers (duration <1 month) to develop E. histolytica diarrhea.
Only an estimated 10%–20% of people infected with E. histolytica become symptomatic. While the specific effect of amebiasis on travel is not well understood, travelers’ diarrhea in general incapacitates about 40% of ill travelers, who have to alter their travel plans for a mean of 2–3 days. Approximately 50 million cases of invasive E. histolytica disease occur each year, with as many as 100,000 deaths. People at high risk for severe disease include pregnant women, immunocompromised people, and patients receiving corticosteroids. Associations with diabetes and alcohol use have also been reported.
Amebic colitis tends to present with more insidious symptoms than bacterial dysentery. Often patients have a 1- to 4-week history of cramps, watery or bloody diarrhea, and weight loss; approximately one-third of patients have fever. Most patients do not have grossly bloody stools, but almost all patients with amebic colitis have stools that test positive for occult blood. Complications of amebic colitis can include acute necrotizing colitis, bowel perforation, toxic megacolon, amebomas, and perianal ulcers with fistula formation.
Occasionally, the parasite may spread to other organs (extraintestinal amebiasis), most commonly the liver. Amebic liver abscesses may be asymptomatic, but most patients present with fever and right upper quadrant abdominal pain, usually in the absence of diarrhea.
Microscopy does not distinguish between the amebas E. histolytica (pathogenic) and E. dispar (nonpathogenic). EIA or PCR is needed to confirm the diagnosis of E. histolytica. Clinicians should contact their state health department reference laboratory for recommendations on E. histolytica–specific testing. The sensitivity of serologic tests varies depending on clinical presentation (approximately 90% extraintestinal and 70% intestinal) and cannot distinguish between current and past infection.
Travelers with either asymptomatic E. histolytica infection or symptomatic E. histolytica disease should be treated if the organism can be proven to be E. histolytica. Otherwise, asymptomatic travelers do not need to be treated. For asymptomatic infection, iodoquinol or paromomycin are the drugs of choice. For symptomatic intestinal infection and extraintestinal disease, treatment with metronidazole or tinidazole should be followed by treatment with iodoquinol or paromomycin.
PREVENTIVE MEASURES FOR TRAVELERS
No vaccine is available to prevent amebiasis, and there is no recommended chemoprophylaxis. To prevent infection, travelers should be advised to follow food and water precautions (including those for ice) described in Chapter 2, Food and Water Precautions. Additionally, travelers should practice good hygiene (including frequent handwashing) and avoid fecal exposure during sexual activity.
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