Antigenic variation is an immune evasion strategy used by some pathogens. It involves the periodic changing of surface proteins (antigens) presented to the host's immune system. After the host mounts an effective immune response (e.g., antibodies) against the current surface antigen, a subpopulation of parasites switches to expressing a different variant surface protein (VSP). The existing antibodies are no longer effective, allowing the new variant to proliferate and cause a renewed infection or chronicity. This creates a moving target for the immune system. Among the parasites discussed, Giardia lamblia is a prime example. It possesses a large repertoire of variant-specific surface proteins (VSPs) covering its entire surface. It can switch VSPs every 6-12 generations. This mechanism is thought to contribute to chronic and recurrent giardiasis, as the host's immune system struggles to keep up with the changing antigenic profile, and may explain why people can be reinfected with the same strain.

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Zambia

• ivwananji siwale – 29 pts

• Visual Pathway Lesions
• Positive and Negative Symptoms
• Hallucinations and Delusions
• Antipsychotic Medications
• Emergency: Environmental Emergencies