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AFRICAN TRYPANOSOMIASIS

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INTRODUCTION

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African trypanosomiasis (sleeping sickness) is a parasitic disease transmitted by the tsetse fly of the genus Glossina and caused by a group of parasites called trypanosomes. Two forms of human African trypanosomiasis are prevalent, specific to the parasite causing illness: Trypanosoma brucei gambiense (Gambian form) is found in West and Central Africa and accounts for 98% of reported cases; and Trypanosoma brucei rhodesiense (Rhodesian form) is found in southern and East Africa. Both forms of the illness are present only in Uganda, but in separate zones.

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PATHOGENESIS AND EPIDEMIOLOGY

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African trypanosomiasis has a focal distribution but expands outward during epidemics. About 65 million people live in risk areas, and in 1998, the World Health Organization estimated a continent-wide prevalence of both forms of African trypanosomiasis of 300,000 cases. In 2009, the number of cases reported fell below 10,000 for the first time in 50 years and has continued to decrease since that time, with less than 4000 cases reported in 2014. Thirty-six sub-Saharan countries are considered endemic for 1 or the other form of the disease. The Gambian form continues to be a major public health problem over vast areas of Africa, from Sudan in the north to northwest Uganda to the Democratic Republic of the Congo to Angola in the south. The Rhodesian form continues to present a serious health risk in the Lake Victoria Basin, particularly in eastern Uganda, and there are small pockets of disease endemic in other countries of East and Central Africa. A line drawn from north to south through sub-Saharan Africa, roughly following the Rift Valley, differentiates the distribution of the 2 diseases with the Gambian form to the west and the Rhodesian form to the east of this notional line. T brucei rhodesiense is a zoonotic parasite, and wild and domestic animals serve as reservoirs. A number of domestic animals species, including pigs, dogs, goats, sheep, and cattle, may carry human-infective trypanosome species. For T brucei gambiense, the nature of animal reservoirs and their role in disease transmission are somewhat less certain.

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Infection occurs equally among males and females. Although children are infected less frequently because of a decreased risk of exposure. Early central nervous system (CNS) involvement and a fulminant course are more common in children.

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All members of the T brucei complex share a common morphology, biochemistry, and life cycle (Fig. 350-1). Infective metacyclic trypomastigotes are inoculated into subcutaneous tissue of a human or another mammalian host by a bite from the tsetse fly. They are converted to the pleomorphic blood forms, which can take long, slender forms, or stumpy forms. Within the human host, trypomastigotes multiply in blood, lymph, and extracellular spaces. The CNS eventually is invaded, where multiplication continues unabated. The tsetse fly is infected with ingestion of a blood meal. Trypomastigotes differentiate into procyclic forms in the midgut, ...

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