West Nile Viruses are spherical particles that are 50 nm in diameter and consist of mainly a membrane envelope and a dense core. The virus contains a positive, single-stranded RNA genome that is packaged within the core protein C. The viral envelope protein is composed of envelope E and membrane M proteins that are embedded in a lipid bilayer. The E protein has important biological roles, which include virion assembly, cell receptor recognition, fusion with cell endosomal membranes, agglutination of red blood cells, and induction of B and T cell responses that are associated with protective immunity.

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