Entomological studies at an enzootic Venezuelan equine encephalitis virus focus in Guatemala, 1977-1980.

The ecology of several potential mosquito vectors of Venezuelan equine encephalitis (VEE) alphavirus was studied in an enzootic focus of that virus on the Pacific coast of Guatemala over a four-year period. Four species-Culex taeniopus, Mansonia titillans, Culex nigripalpus and Aedes taeniorhynchus-were most prevalent during the wet season when transmission normally occurs. However, only Cx. taeniopus yielded VEE virus. The bloodfeeding patterns of these species revealed that Ae. taeniorhynchus and Ma. titillans fed almost exclusively on bovine and equine hosts. Conversely, Cx. nigripalpus was highly ornithophilic but occasionally fed on mammals. Cx. taeniopus exhibited a wide host range, utilizing both large and small mammals as well as birds and, rarely, reptiles. The versatility in feeding pattern displayed by this mosquito coupled with its ability to become infected with relatively low levels of enzootic VEE virus suggests that vertebrates other than rodents may serve as amplifying hosts in this habitat. Nepuyo virus was also isolated from Cx. taeniopus, suggesting that this mosquito might be an endemic vector of this rodent-associated bunyavirus. A single isolate of St. Louis encephalitis virus was made from Cx. nigripalpus.

Mesenteronal infection threshold of an epizootic strain of Venezuelan encephalitis virus in Culex (Melanoconion) taeniopus mosquitoes and its implication to the apparent disappearance of this virus strain from an enzootic habitat in Guatemala.

Culex (Melanoconion) taeniopus is a vector of Venezuelan encephalitis (VE) virus at a marsh focus in Guatemala and has low mesenteronal thresholds for infection by and transmission of two enzootic strains of VE virus. In contrast, samples of natural populations and subsequent F2 and F4 generations of these mosquitoes have a high mesenteronal threshold for infection by an epizootic VE strain isolated at the same marsh during the end of the 1969 VE epidemic-equine epizootic. The resistance of Cu. (Mel). taeniopus to mesenteronal infection by this VE strain probably represents a key factor in the apparent disappearance of epizootic VE virus from the marsh focus following the 1969 outbreak.