Final answer:
Trypanosoma brucei evades the host's immune system through antigenic variation by changing its surface glycoproteins with each generation, preventing the immune system from clearing the infection and contributing to the virulence of African sleeping sickness.
Step-by-step explanation:
Trypanosoma brucei, the causative agent of African sleeping sickness, is known for its ability to evade the human immune system through a process known as antigenic variation. This protozoan parasite changes its surface proteins with each generation by altering the thick layer of surface glycoproteins that the immune system recognizes as foreign. As a result of this variation, T. brucei can replicate continuously, with thousands of potential antigens at its disposal, preventing the immune system from effectively clearing the infection. This antigenic variation contributes to the pathogen's virulence and the undulating form of the initial disease. Without treatment, African sleeping sickness can be fatal due to the damage it causes to the nervous system. T. brucei's capacity for continuous evasion of the immune response is a key survival mechanism that allows it to thrive and cause disease within its host.