WNV Transmission Cycle WNV infections are characterized by a bird-mosquito cycle. On occasion it enters an urban cycle, in which domestic or passerine birds and mosquitoes that prefer to feed on both birds and humans circulate the virus. This European transmission cycle is similar to that of St. Louis encephalitis virus in the United States. Therefore, WNV in the United States is thought to have a similar mode of transmission. WNV has been isolated from a variety of avian species, including crows, ducks and pigeons.
Birds are able to maintain a long-term infection.
Consequently, migratory birds are considered to be instrumental in transporting the virus to new areas. Mammals are less important in maintaining WNV infections. However, WNV has been isolated from several mammalian species. These species include cattle, horses, dogs, and lemurs. Of these animals, only lemurs have been shown to be capable of passing WNV to uninfected mosquitoes during the bloodmeal.