Nestling passerines are not important hosts for amplification of West Nile virus in Chicago, Illinois

Nestling birds have been hypothesized to be important hosts for mosquito-borne arboviruses, but the role of nestlings for West Nile virus (WNV) amplification remains unclear. We sampled open-cup and cavity-nesting passerines in Chicago, Illinois, an area of intense WNV transmission, to determine infection rates in nestlings and mosquitoes, and to test whether mosquitoes are attracted to nesting birds. Analysis of Culex pipiens mosquito populations demonstrated WNV amplification to high mosquito infection rates during both years of the study near the locations where nestlings were sampled. Nevertheless, of 194 nestlings representing 12 species, only one 8-day-old house wren was positive for WNV RNA, and only one 10-day-old mourning dove was seropositive for antibodies to WNV, but at a low titer (1:20). The number of mosquitoes captured in nest box traps and control traps was not significantly different. These combined results suggest that nestling passerines play no evident role in WNV amplification and transmission in the Chicago area.