WEST NILE VIRUS HUMAN CASE PREDICTION, CRYPTIC VECTOR COMMUNITY COMPOSITION, AND FINE-SCALE VIRAL PREVALENCE ACROSS SUBURBAN CHICAGO

Abstract

The Chicago metropolitan area is a hotspot for human West Nile virus (WNV) cases. Despite extensive surveillance and research, predicting WNV cases in Chicago on a local scale is a major challenge. Most studies and mosquito surveillance do not distinguish between two cryptic mosquito species important to WNV transmission, Culex pipiens and Culex restuans, due to the difficulty of distinguishing them. This obscures each species’ respective role in transmission and may blunt the accuracy of local case forecasting. We used species-specific PCR diagnosis to identify Chicago mosquitoes across 21 sites in July and August of 2021 and 2022. We found that Cx. restuans constituted a greater portion of site composition in July compared to August. Culex pipiens was often the sole species recorded from sites in August. We found that site composition can vary dramatically across years. With species identity confirmed, we pooled our specimens and determined infection prevalence using quantitative reverse transcription polymerase chain reaction (RT-qPCR). We found that both species were highly infected with WNV and observed no significant difference in their infection rates between months. We extend our findings to assess the accuracy of a human case prediction model. We found no evidence to support the separation of these species in Chicago WNV surveillance.