How does Trypanosoma brucei evade a host’s immune system?

Trypanosoma brucei, a protozoan responsible for African sleeping sickness, evades the host’s immune system through a process known as antigenic variation.1

When the host’s immune system produces antibodies to neutralize the parasite, T. brucei sheds its surface glycoprotein coat and replaces it with a new coat featuring different amino acid sequences. By continuously changing its surface makeup, the parasite effectively "fools" the immune system, which must then generate an entirely new set of antibodies to recognize the updated variant.1

Each species of the parasite may possess between 100 and 1,000 such antigenic variants, allowing it to replenish its numbers while the host struggles to keep pace with the shifting targets. This sophisticated mechanism of evasion makes the development of an effective vaccine against the disease exceptionally difficult.1