The African trypanosome is a protozoan that, once it enters the blood of human beings and cattle, causes a fatal neurologic disease called trypanosomiasis, or "sleeping sickness" in humans. The key to the trypanosome’s success lies in its ability to evade the host’s immune system via antigenic variation. A mammalian host defends itself against the foreign protozoa by manufacturing specific IgM and IgG antibodies against their variable surface glycoprotein coat (VSG).

The host’s antibodies facilitate the neutralization and killing of approximately 99% of the original protozoan population. However, during this time a few of the trypanosomes have shed their coat, switched VSGs, and covered themselves with a new antigenically distinct VSG coat. These distinct protozoa give rise to a new population expressing the new VSG coats. The immune system again responds to this proliferated population by producing a new set of antibodies that succesfully kill 99% of the trypanosome population. But once again, VSG switching among a small portion of trypanosomes renders them undetectable, and they succesfully evade the host immune response. This cycle continues indefinitely, eventually causing the demise of the host.

Wennchyau Lee is right, Trypanosoma cruzi is an intracellular parasite and the pathogenesis is quite different unlike its counterpart culprit of African sleeping sickness, T. brucei. Thank you for that....

another form of trypanososomiasis is the dourine due to Trypanosoma equiperdum, a venerian disease of equidae (horses); another one, the surra, due to Trypanosoma evansi is mecanicaly transmited by stomoxes, tabanidae.

Vaccine to struggle trypanosomiasis is difficut to discover because parasite antigens are multiple.

As surface antigen of the parasite changes, it is difficult to develop vaccine