Trypanosomes 
Three species of trypanosomes are known to infect man: Trypano- 
soma gambiense and Trypanosoma rhodesiense , etiologic agents of 
African sleeping sickness (African trypanosomiasis) and Trypano- 
soma cruzi, ethologic agent of Chagas’ Disease (American trypanoso- 
miasis). In addition to T. cruzi, a second species, Trypanosoma 
rangeli, has been reported from man and other animals in the western 
hemisphere but has not been included in the charts presented here. 
The life cycles of the two African trypanosomes are similar 
except in the specific fly vector and are shown in a single chart. 
These forms occur in man only in the trypanosomal form and are 
ordinarily located in the blood stream and lymph nodes in the early 
phases of infection and in the central nervous system (primarily 
T. gambiense ) in the chronic phases. They multiply in man by longi- 
tudinal binary fission of the trypanosomes. 
In the arthropod vector, species of tsetse flies, the trypanosomes, 
taken up during the bite, multiply by binary fission in this stage in 
the midgut. They then migrate to the salivary glands where they be- 
come crithidial forms and undergo a second multiplication. In about 2 
to 3 weeks they become metacyclic trypanosomes. These infective 
stage trypanosomes are introduced into the vertebrate host when the 
fly bites again. 
The principal species of tsetse flies which serve as vectors for 
the two trypanosome species are Glossina palpalis and its sub- 
species, G. palpalis fuscipes and G. tachinoides for T. gambiense 
and G. morsitans, G. pallidipes and G. swynnertoni for T , rho- 
desiense, The choice of specific vectors determines to a degree the 
geographical distribution of the trypanosome infections: T, gambiense 
is found chiefly in tropical West and Central Africa and T, rho- 
desiense in northeastern and southern Rhodesia, Nyasaland, Portu- 
guese East Africa, Tanganyika, and Eastern Uganda. 
Wild game mammals such as antelope, probably are reservoir 
hosts for T, rhodesiense, and cattle, hogs, and goats may possibly 
serve as reservoir hosts for T, gambiense, although this has not 
been definitely established. 
The life cycle of T. cruzi is markedly different from that of the 
African trypanosomes. In the mammalian host, two forms, the trypano- 
some and leishmania stages, may be found. The trypanosome form 
usually occurs in the blood stream during the early acute phase and 
during febrile periods. The leishmania stage is found in the tissue, 
usually either reticulo-endothelial cells or heart muscle cells. Occa- 
sionally, they are found within macrophages in the blood. In the 
vertebrate host, the parasite divides only in the leishmania stage. 
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