Final answer:
Trypanosoma brucei evades the host immune system by continuously altering its surface glycoproteins through antigenic variation, causing African sleeping sickness.
Step-by-step explanation:
The parasitic protist known for evading the host immune system by altering its surface proteins with each generation is Trypanosoma brucei. This organism is responsible for African sleeping sickness, a disease that confounds the immune system by changing its surface glycoproteins through a mechanism known as antigenic variation. The immune system mounts a response against these foreign glycoproteins, but due to the vast array of possible antigens that T. brucei can present, the parasite continues to replicate without being eliminated, leading to severe illness and potentially death if not treated.