Susceptibility of Ochlerotatus trivittatus (Coq.), Aedes albopictus (Skuse), and Culex pipiens (L.) to West Nile Virus Infection

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Abstract
The susceptibility of Ochlerotatus trivittatus (Coq.) to West Nile virus (WNV) was assessed by comparing it to the susceptibility of Aedes albopictus (Skuse), a likely bridge vector, and Culex pipiens (L.), a primary WNV amplifying species. The three species were infected with WNV (NY crow–1999) by feeding on 2–3-day-old chickens with serum virus titers ranging from 10 2.5 to 10 9.5 cell culture infective dose (CID) 50s/mL. The lowest infective titer for Oc. trivittatus and Cx. pipiens was 10 4.5 CID50s/mL. Thirteen percent (4/32) and 2% (1/45) of each species became infected postprandially. Infection rates of the two species increased to 43% (6/14) and 15% (6/40) after blood meals with a titer of 10 5.5 CID50s/mL. In contrast no infection was observed in nine Ae. albopictus that fed among three chickens with titers of 10 4.5 CID50s/mL nor in 41 Ae. albopictus that fed among three chickens with titers of 10 5.0 CID50s/mL. The infective dose 50s for Oc. trivittatus, Cx. pipiens and Ae. albopictus were 10 6.0, 10 6.2, and 10 6.6 CID50s/mL, respectively. Collectively these observations suggest that Oc. trivittatus and Cx. pipiens are more susceptible than Ae. albopictus to WNV when they feed on hosts with WNV titers of 7.5 CID50s/mL, but nearly as susceptible with blood meal titers of ≥10 7.5 CID50s/mL. Unpublished studies in our laboratory showed that cottontail rabbits fed on by WNV-infected Oc. trivittatus developed viremias as high as 10 5.5 CID50s/mL serum which exceeds 10 4.2 (3.4-4.6) CID50s/mL, the predicted ID10 ± 95% CI of Oc. trivittatus. Consequently this mosquito, which also feeds on humans and birds has the potential to serve as a bridge vector and as a maintenance vector among mammals.