In people with very weak immune systems, the virus can bring on a serious brain infection called progressive multifocal leukoencephalopathy (PML). PML damages the outer coating of your nerve cells.

West Nile virus is the leading cause of mosquito-borne disease in the continental U.S., according to the CDC. Infections happen during mosquito season, which typically runs from summer through fall.

Large population studies by others found that severe infections, specifically with the cold sore virus, were a strong predictor of Alzheimer's, and that specific antiviral treatment reduced the risk.

Biological scientists have uncovered how the dengue virus uses its envelope protein to capture human plasmin from a blood meal to enhance the permeability of the mosquito midgut for infection.