Vertical transmission of West Nile virus by Culex and Aedes species mosquitoes.

Experiments were conducted to determine whether West Nile (WN) virus was transmitted vertically by colonized strains of Aedes albopictus, Ae. aegypti, and Culex tritaeniorhynchus. Female mosquitoes were infected by intrathoracic inoculation with WN virus, and the F1 progeny were tested for virus by the fluorescence antibody technique and the newborn mouse assay. Each of the three mosquito species transmitted WN virus to F1 adults derived from immature forms reared at 26 degrees C. The minimal filial infection rate (MFIR) ranged from 1:124 to 1:138 for Ae. albopictus, from 1:62 to 1:172 for Ae. aegypti, and from 1:325 to 1:859 for Cx. tritaeniorhynchus. The MFIR for Cx. tritaeniorhynchus reared at 20 degrees C was 1:213 for larvae and 1:390 for pupae, and 1:208 for larvae and 1:554 for pupae reared at 26 degrees C. These data are the first reported evidence of vertical transmission of WN virus by mosquitoes, and therefore warrant further studies to determine whether vertical transmission occurs among WN viral-infected mosquitoes in nature.