Experimental transmission of West Nile virus by Culex nigripalpus from Honduras

As a result of concerns regarding the geographic spread of West Nile virus (WNV) to Central America, we evaluated the potential for Honduran Culex nigripalpus Theobald to transmit this virus. We tested individual mosquitoes captured in Olancho Province, Honduras, in September 2003. Mosquitoes were allowed to feed on 2- to 4-day-old chickens previously inoculated with a New York strain (Crow 397-99) of WNV. Infection rates in Cx. nigripalpus ranged from 81%-96% after feeding on chickens with viremias between 10(6.3) and 10(7.4) plaque-forming units per milliliter. Development of a disseminated infection was directly correlated with holding time after the infectious blood meal as 68% (19/28) of the mosquitoes tested 20 days after the infectious blood meal had a disseminated infection as compared to 38% (15/40) of the mosquitoes tested 14 days after feeding on the same viremic chickens (viremia = 10(6.9-7.1)). Nearly all (4/5) Cx. nigripalpus with a disseminated infection that fed on susceptible chickens transmitted virus by bite. In addition, 8 (57%) of 14 Cx. nigripalpus with a disseminated infection transmitted virus when tested by a capillary tube feeding assay. Based on its efficiency of viral transmission in this study and its role in the transmission of the closely related St. Louis encephalitis virus in the southeastern United States, Cx. nigripalpus should be considered a potentially important vector of WNV in Honduras and the rest of Central America.