African Trypanosomiasis (African Sleeping Sickness)
Description
Trypanosomiasis is a systemic disease caused by the parasite Trypanosoma brucei. East African trypanosomiasis is caused by T. b. rhodesiense, and West African trypanosomiasis by T. b. gambiense. It is transmitted by the bite of the tsetse fly, a gray-brown insect about the size of a honeybee.
Occurrence
African trypanosomiasis is confined to tropical Africa between 15° north latitude and 20° south latitude, or from north of South Africa to south of Algeria, Libya, and Egypt. According to WHO 45,000 cases of trypanosomiasis were reported in 1999, however the actual prevalence of cases is estimated to be between 300,000 to 500,000.
Risk for Travelers
Tsetse flies inhabit rural areas only, living in the woodland and thickets of the savannah and the dense vegetation along streams. Although infection of international travelers was considered rare, the number of cases in travelers, primarily to East African game parks, has increased in recent years. Approximately 1 case per year has been reported among U.S. travelers. Travelers visiting game parks and remote areas should be advised to take precautions. Travelers to urban areas are not at risk.
Clinical Presentation
Signs and symptoms are initially nonspecific (fever, skin lesions, rash, edema, or lymphadenopathy); however, the infection progresses to meningoencephalitis. Symptoms generally appear within 1 to 3 weeks of infection. East African trypanosomiasis is more acute clinically, with earlier central nervous system involvement than in the West African form of the disease. Untreated cases are eventually fatal.
Prevention No vaccine is available to prevent this disease. Tsetse flies are attracted to moving vehicles and dark, contrasting colors. They are not affected by insect repellents and can bite through lightweight clothing. Areas of heavy infestation tend to be sporadically
Leishmaniasis
Description
Leishmaniasis is a parasitic disease transmitted by the bite of some species of sand flies. It is an obligate intracellular protozoan. The disease most commonly manifests either in a cutaneous (skin) form or in a visceral (internal organ) form.
Occurrence
Leishmaniasis is found in approximately 90 tropical and subtropical countries around the world and in southern Europe. More than 90% of the world's cases of cutaneous leishmaniasis are in Afghanistan, Algeria, Brazil, Iran, Iraq, Peru, Saudi Arabia, and Syria. However, approximately 75% of the cases that are evaluated in the United States were acquired in Latin America, where leishmaniasis occurs from northern Mexico (rarely in rural southern Texas) to northern Argentina. More than 90% of the world's cases of visceral leishmaniasis occur in Bangladesh, Brazil, India, Nepal, and Sudan. Leishmaniasis is not found in Australia or the South Pacific.
Risk for Travelers
Travelers of all ages are at risk for leishmaniasis if they live in or travel to these areas. Leishmaniasis usually is more common in rural than urban areas, but it is found in the outskirts of some cities. Risk is highest between dusk and dawn. Adventure travelers, Peace Corps volunteers, missionaries, ornithologists, other persons who do research outdoors at night, and soldiers are examples of those who might have an increased risk for leishmaniasis, especially the cutaneous form. Even persons with short stays in leishmaniasis-endemic areas can become infected.
Clinical Presentation
Cutaneous leishmaniasis is characterized by one or more skin sores (either painful or painless, with or without a scab) that develop weeks to months after a person is bitten by infected sand flies. If untreated, the sores can last from weeks to years and often eventually develop raised edges and a central crater. The manifestations of visceral leishmaniasis, such as fever, weight loss, enlargement of the spleen and liver, and anemia, typically develop months, but sometimes years, after a person becomes infected. If untreated, symptomatic visceral leishmaniasis typically is fatal.
Prevention
Vaccines and drugs for preventing infections are not currently available. Preventive measures for the individual traveler are aimed at reducing contact with sand flies. Travelers should be advised to avoid outdoor activities when sand flies are most active (dusk to dawn). Although sand flies are primarily nighttime biters, infection can be acquired during the daytime if resting sand flies are disturbed. Sand fly activity in an area can easily be underestimated because sand flies are noiseless fliers and rare bites might not be noticed.
Travelers should be advised to use protective clothing and insect repellent for supplementary protection. Clothing should cover as much of the body as possible and be tolerated in the climate. Repellent with N,N-diethylmetatoluamide (DEET) should be applied to exposed skin and under the edges of clothing, such as under the ends of sleeves and pant legs. DEET should be applied according to the manufacturer's instructions; repeated applications may be necessary under conditions of excessive perspiration, wiping, and washing. Although impregnation of clothing with permethrin can provide additional protection, it does not eliminate the need for repellent on exposed skin and should be repeated after every five washings.
Contact with sand flies can be reduced by using bed nets and screens on doors and windows. Fine-mesh netting (at least 18 holes to the linear inch; some sources advise even finer) is required for an effective barrier against sand flies, which are about one-third the size of mosquitoes. However, such closely woven bed nets might be difficult to tolerate in hot climates. Impregnating bed nets and window screens with permethrin aerosol can provide some protection, as can spraying dwellings with insecticide.
Treatment Travelers should be advised to consult with an infectious disease or tropical medicine specialist for diagnosis and treatment. The relative merits of various treatment modalities, including parenteral, oral, local, or topical treatments, can be discussed with the specialist. Physicians may consult with CDC to obtain information about the treatment of leishmaniasis.
Onchocerciasis (River Blindness)
Description
Onchocerciasis is caused by the prelarval (microfilaria) and adult stages of the nematode Onchocerca volvulus. The disease is transmitted by the bite of certain species of female Simulium flies (black flies) that bite by day and are found near rapidly flowing rivers and streams.
Occurrence
Onchocerciasis is endemic in more than 25 nations located in a broad band across the central part of Africa. Small endemic foci are also present in the Arabian Peninsula (Yemen) and in the Americas (Brazil, Colombia, Ecuador, Guatemala, southern Mexico, and Venezuela).
Risk for Travelers
Those traveling for short periods in onchocerciasis-endemic regions appear to be at low risk for acquiring this condition. However, those who visit or live in endemic regions for >3 months and live or work near black fly habitats are at greater risk for infection. Infections tend to occur in expatriate groups such as missionaries, field scientists, and Peace Corps volunteers.
Clinical Presentation
Infection with O. volvulus can result in dermatitis; subcutaneous nodules; lymphadenitis; and ocular lesions, which can progress to blindness. Symptoms may occur months to years after departure from endemic areas.
Prevention
No vaccine and no effective chemoprophylaxis are available. Protective measures include avoidance of black fly habitats and the use of personal protection measures against biting insects.
Treatment
Ivermectin is the drug of choice for onchocerciasis. Repeated oral doses are required for up to several years, because the drug kills the microfilaria but not the adult worm. Travelers should be advised to consult with a specialist in infectious diseases or tropical medicine.
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