Detection of West Nile virus activity in male and female mosquitoes, and evaluation of host-utilization patterns of mosquitoes, in East Baton Rouge Parish, Louisiana

Abstract

Host utilization patterns of female mosquitoes, and WNV infection rates in male and female mosquitoes, were examined in East Baton Rouge Parish to identify potential vectors of West Nile virus (WNV). A total of 244,374 female mosquitoes were collected between November 2002 and October 2004 and tested by viral isolation. Additionally, 131,896 female mosquitoes were tested by VecTest in 2003, and 167,175 female mosquitoes were tested by RT-PCR in 2004. West Nile virus was isolated from 17 of 36 mosquito species assayed by virus isolation, WNV antigens were detected in 9 of 27 species tested by VecTest, and WNV RNA was detected in 14 of 28 mosquito species tested by RT-PCR. The species with the greatest number of WNV positive pools by all 3 testing methods was Culex quinquefasciatus. The Terminal Restriction Fragment Length Polymorphism assay and direct sequencing were used to determine the host bloodmeal identity in 37 bloodfed Cx. coronator, 67 bloodfed Cx. salinarius, 114 bloodfed Cx. nigripalpus, and 686 bloodfed Cx. quinquefasciatus. The proportions of bloodmeals containing mammalian DNA were 94.6% for Cx. coronator, 82.1% for Cx. salinarius, 66.1% for Cx. nigripalpus, and 40.1% for Cx. quinquefasciatus. The White-tailed Deer was the most common host of Cx. coronator and Cx. salinarius. The most common mammalian host of Cx. nigripalpus and Cx. quinquefasciatus was the Northern Raccoon. Human DNA was detected in 7% of the bloodmeals of Cx. quinquefasciatus and 2.7% of the bloodmeals of Cx. nigripalpus. The Northern Cardinal was the most frequent avian host of Cx. quinquefasciatus and Cx. nigripalpus. There was no seasonal change in the monthly proportion of females of Cx. nigripalpus and Cx. quinquefasciatus feeding on mammals from May through October, in either 2003 or 2004. A total of 45 pools containing 171 males of 12 species were assayed for the presence of WNV by virus isolation, and 148 pools containing 7230 males of 15 mosquito species were tested by RT-PCR. Virus was isolated from single pools of male Cx. salinarius and Oc. triseriatus. Single pools containing male Cx. restuans, Ps. howardii, Oc. triseriatus and An. crucians were positive for WNV RNA.