Etiology

There are two forms of human sleeping sickness in Africa. An acute form caused by Trypanosoma brucei rhodesiense with a short incubation period of 5 to 7 days occurs in eastern and southern Africa.

Figure VΠI.2.1. Glossina palpalis.

two large blocks of lowland rain forest in western and central Africa as well as the fringing gallery forests along waterways, which extend into neighbor­ing savanna regions. The morsitans group, or sa­vanna tsetse, is the vector for T. b. rhodesiense, the cause of the rhodesiense form of sleeping sickness; it includes Glossina morsitans (see Figure VIII.2.2), Glossina pallidipes, and Glossina Swynnertoni, which live in the savanna woodlands of eastern and southern Africa (see Maps VIII.2.1 and VIII.2.2). Although tsetse flies are not easily infected with trypanosomes, once infected they remain vectors of the disease for life.

After being bitten by an infected fly, most victims experience local inflammation, or the trypanosomal chancre; and parasites migrate from this site to mul­tiply in blood, lymph, tissue fluids, and eventually the cerebrospinal fluid. The blood trypanosome count oscillates cyclically, with each successive wave, or parasitemia, manifesting different surface antigens. In this manner, trypanosomes evade anti­bodies raised by the host to their previous surface coats. (This antigenic variability has helped to make

Figure VIII.2.2. Glossina morsitans.

the trypanosome one of the most researched patho­genic parasites and a particular favorite with mo­lecular biologists today [Warren, personal communi­cation].) Eventually, all organs are invaded, with central nervous system involvement ultimately lead­ing to death.