West Nile Virus Antibodies in Free-Living North Dakota Icterids

摘要

West Nile virus (WNV) has resulted in the deaths of tens of thousands of North American birds, but population-level effects of the virus remain poorly understood. Breeding birds and nestlings may be particularly vulnerable to WNV because many species nest in close proximity to mosquito breeding habitats and newly hatched chicks lack defensive mechanisms against mosquitoes. To determine the prevalence and potential reproductive impacts of WNV in central North Dakota blackbird populations, we captured and tested 171 free-living icterids for WNV-specific antibodies during the 2003 and 2004 breeding seasons. During the 2004 breeding season, we also trapped and tested 291 female Culex tarsalis, a known WNV vector, for WNV RNA. Five icterids were positive for WNV antibodies, including two adult Yellow-headed Blackbirds (Xanthocephalus xanthocephalus), an adult Common Grackle (Quiscalus quiscula), an adult Red-winged Blackbird (Agelaius phoeniceus), and a juvenile Western Meadowlark (Sturnella neglecta). In contrast, all C. tarsalis were negative for WNV RNA. Our results suggest that WNV infection rates were low in our study area during the 2003 and 2004 breeding seasons, with 3.7 and 2.6% of captured icterids expressing WNV-specific antibodies respectively. However, difficulty in capturing infected individuals and virus-induced lethality could influence WNV infection rate estimates in free-living bird populations.