Evidence for West Nile virus spillover into the squirrel population in Atlanta, Georgia.
BACKGROUND
In the United States, spillover of West Nile virus (WNV) into wild mammal populations has been reported since the introduction of the virus into the New World in 1999. Eastern gray squirrels (Sciurus carolinensis) exhibit a high seroprevalence for WNV in urban settings where high virus circulation and human spillover have been reported. In Atlanta, Georgia, human cases of WNV are uncommon despite high infection rates in birds and mosquitoes. In this study, we evaluated WNV exposure of eastern gray squirrels in a WNV hot spot in Atlanta.


MATERIALS AND METHODS
Gray squirrels were live-trapped in Grant Park, Atlanta, during July-October, 2012, and a census was conducted to estimate squirrel density in the study site. Sera from trapped animals were tested for circulating virus-by-virus isolation in cell culture and for WNV-specific antibodies by enzyme-linked immunosorbent assay and plaque reduction neutralization test. Mosquitoes were collected at the same location and tested for virus isolation.


RESULTS
Among the 69 collected squirrels, 25 (36.2%) tested positive for WNV antibodies, although none were viremic. Seroprevalence was lower in juveniles (18.8%) than in adults (37.5%), but this difference was not statistically significant. Gender and squirrel density had no effect on seroprevalence. Seasonality of squirrel seroprevalence and of mosquito infection were significantly associated, both peaking in August. No difference in squirrel exposure was detected across the collection sites.


CONCLUSIONS
We report a high degree of WNV exposure in squirrels in Grant Park that was correlated with seasonality of mosquito infection. The detection of antibodies in juveniles suggests that circulation of WNV in the surveyed population is ongoing. Eastern gray squirrels may be suitable indicators for virus amplification and for risk of human spillover on a local scale in urban settings.
['Bisanzio|Donal|D|', 'McMillan|Joseph R|JR|', 'Barreto|Josafá Gonçalves|JG|', 'Blitvich|Bradley J|BJ|', 'Mead|Daniel G|DG|', "O'Connor|Josh|J|", 'Kitron|Uriel|U|']
D000818:Animals D000914:Antibodies, Viral D001717:Birds D009033:Culicidae D004797:Enzyme-Linked Immunosorbent Assay D006801:Humans D009500:Neutralization Tests D012589:Sciuridae D016036:Seroepidemiologic Studies D014481:United States D014901:West Nile Fever D014902:West Nile virus D015047:Zoonoses
West Nile Virus Gray squirrels Arbovirus(es) Culex Rodents Zoonosis