Ecology of Keystone virus, a transovarially maintained arbovirus

Our studies in the Pocomoke Cypress Swamp of Maryland have shown that KEY strain of CE is endemic and is carried by the floodwater mosquito A. atlanticus. The virus is transmitted transstadially in nature, as evidenced by our recovery of virus from larvae and males of this species. Serologic evidence, both here and elsewhere, indicates that vertebrates are infected with KEY, but their role in the transmission cycle remains unknown. We have found several animals, for example, the gray squirrel, that are potential vertebrate reservoirs for the virus. Gray squirrels possess antibodies to KEY in nature, are known to be fed upon by A. atlanticus females, and have been shown to circulate a high-titered viremia after experimental inoculation. Evidence from 1974 collections, however, indicates that A. atlanticus females ingested only a single blood meal during the period when adults were active. We will not be able to assess the relative importance of the vertebrate and mosquito cycles until much more work has been performed on vector-reservoir-virus dynamics.