Eastern equine encephalitis virus in mosquitoes and their role as bridge vectors

Abstract

Eastern equine encephalitis virus (EEEV) is maintained in an enzootic cycle involving Culiseta melanura mosquitoes and avian hosts. Other mosquito species that feed opportunistically on mammals have been incriminated as bridge vectors to humans and horses. To evaluate the capacity of these mosquitoes to acquire, replicate, and potentially transmit EEEV, we estimated the infection prevalence and virus titers in mosquitoes collected in Connecticut, USA, by cell culture, plaque titration, and quantitative reverse transcription-PCR. Cs. melanura mosquitoes were the predominant source of EEEV (83 [68%] of 122 virus isolations) and the only species to support consistently high virus titers required for efficient transmission. Our findings suggest that Cs. melanura mosquitoes are primary enzootic and epidemic vectors of EEEV in this region, which may explain the relative paucity of human cases. This study emphasizes the need for evaluating virus titers from field-collected mosquitoes to help assess their role as vectors.

Figure

Relationship between cycle threshold value and PFU estimated from eastern equine encephalitis virus–infected mosquito pools, Connecticut, USA, 2009. Mosquito pools negative for virus by plaque titration were assigned a value of 0, and mosquito pools negative by quantitative reverse transcription–PCR were assigned a value of 50. Limit of detection by plaque titration (0.8 log₁₀ PFU/mL) is indicated by the dashed vertical line.