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Vector-Borne Diseases: Trypanosomiasis

Vector-Borne Diseases: Trypanosomiasis. April 1 st , 2010. The Pathogen. Genus Trypanosoma Two species of human health importance: Trypanosoma brucei Trypanosoma cruzi The T. brucei complex (2 subspecies): Trypanosoma brucei rhodesiense Trypanosoma brucei gambiense

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Vector-Borne Diseases: Trypanosomiasis

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  1. Vector-Borne Diseases:Trypanosomiasis April 1st, 2010

  2. The Pathogen • Genus Trypanosoma • Two species of human health importance: • Trypanosoma brucei • Trypanosoma cruzi • The T. brucei complex (2 subspecies): • Trypanosoma brucei rhodesiense • Trypanosoma brucei gambiense • Cannot tell them apart by morphology • Cause distinct disease entities

  3. The Pathogen • Protozoan hemoflagellates • Single celled • flagella • Complex life cycle • Vector • Human • animals • Reservoirs: • Humans • Cattle

  4. The Pathogen Trypanosoma brucei ssp. in thin blood smears stained with Giemsa.

  5. Overview • Three types of trypanosomiasis • West African (sleeping sickness) • East African (sleeping sickness) • American (Chaga’s disease) • Differences • Geographic distribution • Vectors • Disease process

  6. West African Trypanosomiasis • Sleeping sickness • Trypanosoma brucei gambiense • Geographic distribution • Western and Central Africa • Vector distribution • Always fatal without treatment • Disease course over years • acute and chronic phases

  7. West African Trypanosomiasis • This form is ~95% of reported cases • 12,000-15,000 reported cases/year, WHO estimates 50-60,000 are really infected • Humans are the reservoir • Disease of rural areas; urban transmission is rare

  8. East African Trypanosomes • Trypanosoma brucei rhodesiense • Geographic distribution • East and Southeast Africa • Always fatal without treatment • Acute course compared to gambiense form • Cattle are additional reservoir

  9. Cases of African trypanosomiasis

  10. Geographic distribution

  11. Geographic distribution

  12. The vector • Tsetse fly • Glossina species • Takes a blood meal • trypomastigotes are the form transmitted to the host • Daytime feeder • Savannah and riverine flies

  13. Life Cycle: Trypanosomes

  14. Disease • Length of disease process differs between two • Sore may develop at site of initial inoculation • hemolymphatic stage • fever, lymphadenopathy, and pruritus.  • meningoencephalitic stage • Parasite crosses blood-brain barrier • invasion of the central nervous system • headaches, somnolence, abnormal behavior • loss of consciousness and coma • more acute disease with T. b. rhodesiense than T. b. gambiense.

  15. Immunity • Humans do mount immune response • No residual immunity • cyclic fluctuation in the number of parasites in blood • Each new wave of parasite represents a different antigenic variant

  16. Diagnosis • Microscopic examination • chancre fluid • lymph node aspirates • Blood • bone marrow • cerebrospinal fluid (late stages of infection)  • smear stained with Giemsa

  17. Treatment • Pentamidine isethionate • hemolymphatic stage of West African • suramin • hemolymphatic stage of East African • Melarsoprol • arsenical • late disease with central nervous system involvement • T.b. gambiense or T. b. rhodiense • Eflornithine • Expensive • not widely available • effective only for West African

  18. Control • Bite prevention • Difficult with daytime biters • Control vector habitats • Treat infected people • Screening methods are available • Bednets not useful

  19. Vector control • Control with insecticides • sequential aerosol spraying technique (SAT) • ground spraying • insecticide-treated targets or insecticide-treated animals • Traps • sterile insect technique (SIT).

  20. American trypanosomiasis • Chaga’s Disease • Trypanosoma cruzi • Geographic distribution • southern United States to southern Argentina • A disease of poor, rural areas of Mexico, Central America, and South America • Humans and animals are reservoir

  21. Geographic distribution

  22. Vector • triatomine bugs (kissing bugs) • Triatoma, Rhodinius, and Panstrongylus • Takes a blood meal • Releases trypomastigotes in its feces near the site of the bite • Enter host through the wound

  23. Life Cycle: Chaga’s disease

  24. Disease • Acute phase • usually asymptomatic • fever, anorexia, lymphadenopathy, myocarditis • Lesion (chagoma) at site of inoculation • Resolve over a period of a few weeks or months into an asymptomatic chronic form • 20-30% of cases • Years or decades after initial infection: • cardiomyopathy • GI complications • can be fatal

  25. Diagnosis • Microscopic examination • fresh anticoagulated blood • thin and thick blood smears stained with Giemsa • Isolation of the agent: • inoculation in culture with specialized media • inoculation into mice • xenodiagnosis

  26. Treatment • Benznidazole • nifurtimox • Treatment is most effective during the acute phase • Drugs are fairly toxic • IND protocol from the CDC

  27. Control • Vector control • Poorly constructed houses and houses with thatched roofs are at risk • Treatment of houses with insecticides • Get rid of places in dwellings where vector and reservoir animals can live and breed • Bednets

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