Culex torrentium Mosquito Role as Major Enzootic Vector Defined by Rate of Sindbis Virus Infection, Sweden, 2009.

Jenny C Hesson,Jenny Verner-Carlsson,Anders Larsson,Åke Lundkvist,Raija Ahmed,Jan O Lundström

doi:10.3201/eid2105.141577

Abstract

We isolated Sindbis virus (SINV) from the enzootic mosquito vectors Culex torrentium, Cx. pipiens, and Culiseta morsitans collected in an area of Sweden where SINV disease is endemic. The infection rate in Cx. torrentium mosquitoes was exceptionally high (36 infections/1,000 mosquitoes), defining Cx. torrentium as the main enzootic vector of SINV in Scandinavia.

Highlights

We isolated Sindbis virus (SINV) from the enzootic mosquito vectors Culex torrentium, Cx. pipiens, and Culiseta morsitans collected in an area of Sweden where SINV disease is endemic
The results showed that all new strains belonged to the SINV-I genotype and have close relationships with strains from Europe, the Middle East, and South Africa (Figure)
The significantly higher SINV-I infection rates (IRs) observed for field-caught Cx. torrentium than Cx. pipiens mosquitoes is a key addition to the previous findings of the extreme susceptibility of Cx. torrentium mosquitoes to SINV-I (4)

Summary

Total estimates

Mixed species (Cx. pipiens and Cx. torrentium), respectively. Cs. morsitans mosquitoes were tested in pools, so we calculated the minimum IR (MIR) as Mosquitoes tested) × 1,000; the calculated MIR was 6.9 infections/1,000 Cs. morsitans mosquitoes. A comparison of MIR and maximum-likelihood estimates of infection gave similar estimates. SINV was successfully isolated from all 16 rRT-PCR– positive mosquito samples (Table 2). Part of the SINV E2 envelope glycoprotein gene was sequenced as previously described (8). The phylogenetic analysis included all genomic sequences obtained in this study together with previously published sequences for 63 other virus strains (8). The results showed that all new strains belonged to the SINV-I genotype and have close relationships with strains from Europe, the Middle East, and South Africa (Figure)

Conclusions

Findings

Culex torrentium Mosquito as Major Enzootic Vector