How does Trypanosoma brucei evade the human immune system?

Trypanosoma brucei evades the human immune system through a sophisticated mechanism known as antigenic variation.1

The parasite is covered in a glycoprotein coat that the host's immune system recognizes and targets with specific antibodies. Just as the immune system begins to successfully neutralize the majority of the parasite population, T. brucei sheds its surface coat and replaces it with a new one featuring different amino acid sequences.1

These alternate forms are called antigenic variants, and it is estimated that each species can produce between 100 and 1,000 distinct variations. Because the host must generate an entirely new set of antibodies to recognize each new variant, the parasite gains the necessary time to replenish its numbers and continue the infection. This constant shifting of its chemical makeup makes the development of an effective vaccine against the parasite virtually impossible.1