Detection of West Nile Virus RNA in Mosquitoes and Identification of Mosquito Blood Meals Collected at Alligator Farms in Louisiana

Abstract

Since 2001, alligator farms in the United States have sustained substantial economic losses because of West Nile virus (WNV) outbreaks in American alligators (Alligator mississippiensis). Once an initial infection is introduced into captive alligators, WNV can spread among animals by contaminative transmission. Some outbreaks have been linked to feeding on infected meat or the introduction of infected hatchlings, but the initial source of WNV infection has been uncertain in other outbreaks. We conducted a study to identify species composition and presence of WNV in mosquito populations associated with alligator farms in Louisiana. A second objective of this study was to identify the origin of mosquito blood meals collected at commercial alligator farms. Mosquitoes were collected from 2004 to 2006, using Centers for Disease Control light traps, gravid traps, backpack aspirators, and resting boxes. We collected a total of 58,975 mosquitoes representing 24 species. WNV was detected in 41 pools of females from 11 mosquito species: Anopheles crucians, Anopheles quadrimaculatus, Coquillettidia perturbans, Culex coronator, Culex erraticus, Culex nigripalpus, Culex quinquefasciatus, Mansonia titillans, Aedes sollicitans, Psorophora columbiae, and Uranotaenia lowii. The blood meal origins of 213 field-collected mosquitoes were identified based on cytochrome B sequence identity. Alligator blood was detected in 21 mosquitoes representing six species of mosquitoes, including Cx. quinquefasciatus and Cx. nigripalpus. Our results showed that mosquitoes of species that are known to be competent vectors of WNV fed regularly on captive alligators. Therefore, mosquitoes probably are important in the role of transmission of WNV at alligator farms.

Host Selection of Potential West Nile Virus Vectors in Puerto Barrios, Guatemala, 2007

“…nigripalpus were found to have fed on captive alligators in Louisiana. 45 A high rate of feeding on reptiles and amphibians was reported for Cx. quinquefasciatus in Puerto Rico during a period of elevated WNV transmission.…”

Entomologic Investigations during an Outbreak of West Nile Virus Disease in Maricopa County, Arizona, 2010

“…columbiae is of interest, in light of research identifying WNV in nine pools of this species in New Mexico, 31 and in two pools captured at alligator farms in Louisiana. 32 Although this species seems to feed preferentially on livestock, 33 the degree to which it also feeds on small mammals, birds, or other vertebrates is not known. Our three positive pools came from a single outbreak site, a horse ranch, and those in New Mexico came primarily from semi-arid or agricultural sites.…”

West Nile Virus

“…Until its first detection in birds in Aus- viremic phase of infection in species such as humans or horses is in general too low to enable the infection of mosquitoes. However, it was shown by experimental infection that some mammalian species like fox squirrels (Sciurus niger) [129] or reptiles such as alligators [130] develop a viremia high enough to infect mosquitoes. In several European countries like France and Italy, WNV infections in horses were considered as the first signs of invasion of the pathogen into these regions [74,78].…”

“…This was demonstrated both by examining the progeny of experimentally infected mosquitoes as well as by virus isolation from male mosquitoes which must have been infected vertically because males do not take blood meals but rather feed on plant juice [130,150]. The transovarial transmission of the virus may be important for the maintenance of the infection cycle between mosquitoes and birds, as it has been shown that mosquitoes were infected with WNV during the winter diapause without having taken a blood meal [148].…”