West Nile Virus Infection Rates in <I>Culex nigripalpus</I> (Diptera: Culicidae) Do Not Reflect Transmission Rates in Florida

Abstract

We describe the first documented field transmission of West Nile (WN) virus by a North American mosquito. WN was first detected in northern Florida in 2001. An intensive mosquito trapping and surveillance program was conducted in this region for four nights to assess mosquito transmission of WN. Four mosquito traps, each with a single sentinel chicken, were placed at five different locations on each of four nights. A total of 11,948 mosquitoes was collected, and 14 mosquito pools were found to contain WN, giving a minimum infection rate between 1.08 and 7.54 per 1,000. Only one of the 80 sentinel chickens seroconverted to WN, demonstrating a single mosquito transmission event during the study and a mosquito transmission rate of between 0.8 and 1 per 1,000. Culex nigripalpus Theobald was responsible for WN transmission to the sentinel chicken, although both Cx. nigripalpus and Culex quinquefasciatus Say were found infected with WN. Mosquito transmission rates are reported in this study for the first time for a WN outbreak. This information is essential to determine risk of human and animal infection.

Ecology of Potential West Nile Virus Vectors in Southeastern Louisiana: Enzootic Transmission in the Relative Absence of Culex quinquefasciatus

“…This species is the primary vector for SLEV in southern Florida, 14,15 and WNV was isolated from this species in northern Florida in 2001, the first year that the virus was detected in that state. 16,17 Eight isolates of WNV were obtained during 2005 from Cx. nigripalpus collected in chicken-baited lard can traps placed at three widely dispersed sites in Florida.…”

“…41 This study also noted a low rate of WNV transmission to the chickens restrained within the traps, despite seven of eight virus-positive pools containing only blooded females, a finding that corroborates previous work. 17 Vitek and others 41 speculate that the lack of virus dissemination within the infected mosquitoes may be responsible for the low transmission rate, but their experimental protocol did not allow them to test this idea. 41 In southern Florida, onset of human cases and the appearance of anti-WNV antibodies in sentinel chickens are temporally and spatially associated with prior cycles of drought and moisture in a manner similar to that seen with SLEV, thus providing strong evidence that Cx.…”

“…nigripalpus to a chicken in a baited trap was shown. 17 Despite these studies, a number of questions remained concerning the pattern of transmission that WNV would take in the southern United States, such as the precise roles of different mosquito species in enzootic, epizootic, and epidemic transmission, the habitats that would be most favorable to WNV maintenance by enhancing vector-amplifier host contact, and the effect of an extended transmission season because of milder climatic conditions in the Gulf Coast states.…”

Use of Scented Sugar Bait Stations to Track Mosquito-Borne Arbovirus Transmission in California

“…However, the bulky nature of chicken coops and the cost of maintenance typically Recently, FTA cards (Whatman International Ltd., Maidstone, United Kingdom) impregnated with honey were used to measure Barmah Forest and Ross River virus transmission by host-seeking mosquitoes collected using traps baited with CO 2 gas (HallMendelin et al 2010), thereby exploiting previous laboratory reports that flaviviruses were expectorated during sugar feeding (Doggett et al 2001, van den Hurk et al 2007). Although technically this method provides data similar to avian baits that measure infection and transmission rates (Bellamy and Reeves 1952, Reeves et al 1961, Rutledge et al 2003, the use of honey impregnated cards to collect viral RNA was novel, precluded the use of avian hosts, and allowed trap deployment for longer than a single night. However, the use CO 2 gas to attract host-seeking females failed to take advantage of the fact that most mosquitoes feed repeatedly on fructose throughout the gonotrophic cycle as well as during seasons when gonotrophic activity is suppressed (Reisen et al 1986).…”

“…Although technically this method provides data similar to avian baits that measure infection and transmission rates (Bellamy and Reeves 1952, Reeves et al 1961, Rutledge et al 2003, the use of honey impregnated cards to collect viral RNA was novel, precluded the use of avian hosts, and allowed trap deployment for longer than a single night. However, the use CO 2 gas to attract host-seeking females failed to take advantage of the fact that most mosquitoes feed repeatedly on fructose throughout the gonotrophic cycle as well as during seasons when gonotrophic activity is suppressed (Reisen et al 1986).…”