An Update on the Potential of North American Mosquitoes (Diptera: Culicidae) to Transmit West Nile Virus

Abstract

Since Þrst discovered in the New York City area in 1999, West Nile virus (WNV) has become established over much of the continental United States and has been responsible for Ͼ10,000 cases of severe disease and 400 human fatalities, as well as thousands of fatal infections in horses. To develop appropriate surveillance and control strategies, the identiÞcation of which mosquito species are competent vectors and how various factors inßuence their ability to transmit this virus must be determined. Therefore, we evaluated numerous mosquito species for their ability to transmit WNV under laboratory conditions. This report contains data for several mosquito species not reported previously, as well as a summary of transmission data compiled from previously reported studies. Mosquitoes were allowed to feed on chickens infected with WNV isolated from a crow that died during the 1999 outbreak in New York City. These mosquitoes were tested Ϸ2 wk later to determine infection, dissemination, and transmission rates. All Culex species tested were competent vectors in the laboratory and varied from highly efÞcient vectors (e.g., Culex tarsalis Coquillett) to moderately efÞcient ones (e.g., Culex nigripalpus Theobald). Nearly all of the Culex species tested could serve as efÞcient enzootic or amplifying vectors for WNV. Several container-breeding Aedes and Ochlerotatus species were highly efÞcient vectors under laboratory conditions, but because of their feeding preferences, would probably not be involved in the maintenance of WNV in nature. However, they would be potential bridge vectors between the avianÐCulex cycle and mammalian hosts. In contrast, most of the surface pool-breeding Aedes and Ochlerotatus species tested were relatively inefÞcient vectors under laboratory conditions and would probably not play a signiÞcant role in transmitting WNV in nature. In determining the potential for a mosquito species to become involved in transmitting WNV, it is necessary to consider not only its laboratory vector competence but also its abundance, host-feeding preference, involvement with other viruses with similar transmission cycles, and whether WNV has been isolated from this species under natural conditions.

Bloodmeal identification and feeding habits of mosquitoes (Diptera: Culicidae) collected at five islands in the Ryukyu Archipelago, Japan

“…Although, this species is basically ornithophilic, it is also an opportunistic feeder that feeds readily on mammals including humans in residential areas. This species is regarded as an important vector for WNV (Molaei et al, 2007;Turell et al, 2005), and we suggest it is a candidate bridge vector for WNV in the Ryukyus. Culex ryukyensis of subgenus Culiciomyia fed on mammals (human and wild boar) and a reptile (lizard) in this study.…”

Mathematical assessment of the role of temperature and rainfall on mosquito population dynamics

“…Culex pipiens L.-culex restuans theobald mosquitoes are the two primary WNv vectors in North America. The two species, which prefer water habitats with high organic content for their development cycle (Hilker and Westerhoff 2007;Turell and Dohm 2005), are morphologically the same (DeGaetano 2005). Owing to such similarity, the mosquito surveillance data for the Peel region lumps the two species together (it should be recalled that the model developed in the current study does not also distinguish between the two culex species).…”

“…Statistical study by Hilker and Westerhoff (2007) showed that hatching of the culex mosquito eggs varies during the year; being low in the winter (whenever the temperature is less than 10 • C) and high in the summer (whenever the temperature is in the range (22−30) • C). Rainfall can induce positive (where rainfall increases the availability of breeding sites for female culex mosquitoes to lay their eggs) or negative (excessive rainfall increases the mortality of immature mosquitoes) effect on culex dynamics (Turell and Dohm 2005).…”

“…Furthermore, the maximum values for the rates of eggs hatching, Rainfall ( Table 5 maturation from larvae to pupae and maturation from pupae to adult mosquitoes are taken to be α E = 0.5, α L = 0.35 and α P = 0.5, respectively Clements (1999). Finally, while the peak survival rates of maturation of mosquitoes are recorded at 20 • C (Turell and Dohm 2005), that of mature (adult) mosquitoes occur at 28 • C Turell and Dohm (2005). Hence, we set T * E = T * L = T * P = 20 • C, and T * M = 28 • C. Simulations were started near the trivial equilibrium (January 1, corresponding to t = 1 day) and ran until the end of the year (see attached Matlab code in Appendix C).…”

Overwintering site of Culex pipiens pallens in an urban environment of Saitama Prefecture in Japan

“…pipiens form molestus Forskal and Cx. quiquefasciatus Say, are competent vectors of WNV (Turell et al, 2002(Turell et al, , 2005 and WNV has been isolated frequently from Culex pipiens complex (Anderson et al, 1999;Bernard et al, 2001). Although WNV activity was not detected in eld-collected mosquitoes from our survey during 2003 2006 in Japan, it is also important to know which subspecies of the Culex complex are potential bridge vectors in the urban environment of Japan.…”