[Answer] How is antigenic variation used to evade host defenses?

Answer: the parasite trypanosoma undergoes rapid antigenic variation to evade the
host’s immune response
How is antigenic variation used to evade host defenses?
Antigenic variation allows pathogens to escape from immunity One way in which an infectious agent can evade immune surveillance is by altering its antigens; this is particularly important for extracellular pathogens against which the principal defense is the production of antibody against their surface structures.
Antigenic and phase variation are most often used by microorganisms to evade the host immune response and to adapt to new environments within the host . Several different genetic mechanisms to achieve antigenic or phase variation are well understood thanks to decades of experimental investigation and are the focus of this article.
Antigenic Variation. antigenic variation and immune evasion primarily occur in the antibody neutralizing/blockade epitopes of the capsid P2 domain primarily in epitope A.110–112 NoV quasispecies may also evolve in and emerge from persistent or chronic infections in immunocompromised hosts. From: Plotkin’s Vaccines (Seventh Edition) 2018
Some parasites practice antigenic variation altering their surface antigens during the course of an infection and thus evading the host’s immune responses. Finally the parasite may cause immunosuppression reducing the host’s immune response either to the parasite specifically or to foreign antigens in general.
The success of each pathogen is directly dependant on its…

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