Anne Moore

Infectious Agent

Two subspecies of the protozoan parasite Trypanosoma brucei (T. b. rhodesiense and T. b. gambiense) cause infection.

Mode of Transmission

Infection occurs through vector-borne transmission by the bite of an infected tsetse fly (Glossina spp.). Transmission via bloodborne or congenital routes can occur but is rarely reported.

Occurrence

• HAT is transmitted only in rural sub-Saharan Africa. The two human-infective subspecies of T. brucei do not overlap in geographic distribution.
• T. b. rhodesiense is found in eastern and southeastern Africa. Over 95% of the cases of T. b. rhodesiense infection occur in Tanzania, Uganda, Malawi, and Zambia.
• T. b. gambiense is found predominately in central Africa and in limited areas of West Africa. Over 95% of the cases of T. b. gambiense infection are reported from the Democratic Republic of Congo, Angola, Sudan, Central African Republic, Republic of Congo, Chad, and northern Uganda.

Risk for Travelers

• Infection of international travelers occurs but is rare. On average, a single case per year is reported among U.S. travelers.
• Most infections in U.S. travelers are caused by T. b. rhodesiense and are acquired in East Africa game parks.
• Tsetse flies inhabit rural areas, living in the woodlands and thickets of the savannah and the dense vegetation along streams. Less than 1% of flies are infected in a typical endemic area.
• Tsetse flies bite during daylight hours. Most bites that occur on the African savannah are quite painful, and travelers often recall the bite.
• Travelers to urban areas are not at risk.

Clinical Presentation

• Presentation is variable and depends on the infecting subspecies. Infection with T. b. rhodesiense is more acute clinically and progresses more rapidly than T. b. gambiense.
• Symptoms and signs of T. b. rhodesiense infection generally appear within 1–3 weeks of the infective bite. These may include high fever, a chancre at the site of the infective bite, skin rash, headache, myalgia, thrombocytopenia, and less commonly, splenomegaly, renal failure, or cardiac dysfunction. Central nervous system involvement can occur within the first month of infection.
• Symptoms of T. b. gambiense infection are nonspecific, and patients may remain paucisymptomatic for many months after infection. Symptoms and signs may include fever, headache, malaise, myalgia, facial edema, pruritus, lymphadenopathy, and weight loss. Central nervous system involvement occurs after months of infection and is characterized by somnolence, severe headache, and a wide range of neurologic manifestations, including mood disorders, behavior change, focal deficits, and endocrine disorders.
• Untreated HAT infection is eventually fatal.

Diagnosis

• Microscopic identification of parasites in specimens of blood, chancre fluid or tissue, lymph node aspirate, or cerebrospinal fluid. Buffy coat preparations concentrate the parasite. Parasitemias are higher in T. b. rhodesiense than in T. b. gambiense infection.
• Serologic tests are not helpful for diagnosis of T. b. rhodesiense. CDC can provide information for arranging for serologic testing for T. b. gambiense, which is not available in the United States.
• Diagnostic assistance is available through CDC DPDx (www.dpd.cdc.gov/dpdx).

Treatment

• Travelers who sustain tsetse fly bites and become ill with high fever or other manifestations of African trypanosomiasis are advised to seek early medical attention. The infection can usually be cured by a course of antitrypanosomal therapy.
• HAT is rare in the United States, and the inexperienced physician is advised to consult with an infectious disease or tropical medicine specialist for diagnosis and treatment.
• Physicians can consult with CDC for assistance with diagnosis and clinical management (DPD Public Inquiries, 770-488-7775, ncidpbdpi@cdc.gov).
• Treatment drugs (suramin, melarsoprol, eflornithine) are provided by CDC under investigational protocols.

Preventive Measures for Travelers

• No vaccine or drug for prophylaxis is available.
• Preventive measures are aimed at reducing contact with tsetse flies. Areas of heavy infestation tend to be sporadically distributed and are usually well known to local residents. Avoidance of these areas is the best means of protection.
• Tsetse flies are attracted to moving vehicles and bright, dark colors. Permethrin-impregnated clothing and use of DEET repellent may reduce the number of fly bites. The flies can bite through lightweight clothing. Travelers are advised to wear clothing of wrist and ankle length made of medium-weight fabric in neutral colors that blend with the background environment.

References

1. Braakman HM, van de Molengraft FJ, Hubert WW, Boerman DH. Lethal African trypanosomiasis in a traveler: MRI and neuropathology. Neurology. 2006;66:1094–6.
2. Moore DA, Edwards M, Escombe R, et al. African trypanosomiasis in travelers returning to the United Kingdom. Emerg Infect Dis. 2002;8:74–6.
3. Moore AC, Ryan ET, Waldron MA. Case records of the Massachusetts General Hospital. Weekly clinicopathological exercises. Case 20-2002. A 37-year-old man with fever, hepatosplenomegaly, and a cutaneous foot lesion after a trip to Africa. N Engl J Med. 2002;346:2069–76.
4. Sholdt LL, Schreck CE, Mwangelwa MI, et al.Evaluations of permethrin-impregnated clothing and three topical repellent formulations of DEET against tsetse flies in Zambia. Med Vet Entomol. 1989;3(2):153–8.