Page "West Nile virus" Paragraph 29

Vertical transmission ; the transmission of a viral or bacterial disease from the female of the species to her offspring, has been observed in various West Nile virus studies, amongst different species of mosquitoes in both the laboratory and in nature.

Mosquito progeny infected vertically in autumn, may potentially serve as a mechanism for WN virus to overwinter and initiate enzootic horizontal transmission the following spring.