West Nile Virus: Deaths of Crows and Humans

This chapter addresses West Nile virus, the cause of a formerly unknown disease whose path through America was a trail of dead birds and dead people. West Nile virus is currently the most common and severe form of mosquito-borne encephalitis in North America. At present, West Nile virus has been isolated from over 300 species of birds. The infected birds fall into two major groups: those that carry the virus and are asymptomatic and those that develop an often fatal neurologic disease. Crows, jays, magpies, and house finches, upon infection, develop high virus loads and rapidly infect the mosquitoes that prey on them. House sparrows are also reservoirs for high titers of West Nile virus and play a role in the virus’ transmission in city areas. Humans are incidental/accidental hosts in the natural mosquito–bird cycle of this viral infection. Most humans who become infected have received bites from mosquitoes carrying the West Nile virus. The viruses then replicate at the bite site and likely spread to specialized cells, dendritic cells, which act as processors of foreign antigens. Viruses may also travel directly from the bite site into and through the blood.