Culex torrentium Mosquito Role as Major Enzootic Vector Defined by Rate of Sindbis Virus Infection, Sweden, 2009 - Volume 21, Number 5—May 2015 - Emerging Infectious Disease journal - CDC

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Culex torrentium Mosquito Role as Major Enzootic Vector Defined by Rate of Sindbis Virus Infection, Sweden, 2009 - Volume 21, Number 5—May 2015 - Emerging Infectious Disease journal - CDC

Volume 21, Number 5—May 2015

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

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• The Study
• Conclusions
• Suggested Citation

Figures

• Figure

Tables

• Table 1
• Table 2

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

Author affiliations: Uppsala University, Uppsala, Sweden (J.C. Hesson, J. Verner-Carlsson, A. Larsson, Å. Lundkvist, J.O. Lundström); Public Health Agency of Sweden, Solna, Sweden (J. Verner-Carlsson, R. Ahmed, Å. Lundkvist); Nedre Dalälvens Utvecklings AB, Gysinge, Sweden (J.O. Lundström)

Suggested citation for this article

Abstract

We isolated Sindbis virus (SINV) from the enzootic mosquito vectors Culex torrentium, Cx. pipiens, andCuliseta 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.

In Sweden, Finland, Russia, and South Africa, Sindbis virus (SINV; family Togaviridae, genus Alphavirus) is an etiologic agent for outbreaks of rash and long-lasting polyarthritis (1). Ecologically, SINV is a zoonotic mosquitoborne virus that naturally circulates in bird populations but only incidentally infects humans (1). Previous detections and isolations of SINV from field-collected mosquitoes identified the ornithophilic mosquitoes Culex pipiens/Cx. torrentium and Culiseta morsitans as possible enzootic vectors of SINV and the generalist mosquitoes Aedes cinereus and Ae. rossicus, which feed on birds and humans, as potential bridge vectors for transmission of the virus from viremic birds to humans (2,3; J.C. Hesson, J.O. Lundström, unpub. data). However, female Cx. torrentium and Cx. pipiens mosquitoes are morphologically indistinguishable, so all previous virus isolates from these species were from pools that may have contained both species. The distinction between Cx. torrentium and Cx. pipiens is necessary because vector competence experiments show great differences between the capacities of the 2 species to become infected with and to transmit SINV (4,5). Cx. torrentium is highly superior to Cx. pipiens as a vector of SINV in the laboratory (4,5), but the extent to which the 2 species are infected in nature is unclear.

We determined the natural SINV infection rates (IRs) in Culex mosquitoes, which were identified by using a newly developed molecular method for reliable identification of Cx. torrentium and Cx. pipiens mosquitoes (6). We also studied the simultaneous occurrence of SINV in Cs. morsitans mosquitoes.

Dr. Hesson is a researcher at Uppsala University in Sweden. Her primary research interests are mosquito-borne human pathogens, especially the effect of mosquito ecology on virus transmission.

Acknowledgments

We are grateful to Pernilla Wahlqvist for collecting and identifying mosquitoes and to the Royal Swedish Academy of Sciences and the Zoological Foundation for financial support.

The phylogenetic computations were performed on resources provided by Swedish National Infrastructure for Computing through Uppsala Multidisciplinary Center for Advanced Computational Science (project p2009050).

References

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Figure

• Figure. Consensus tree of the partial E2 envelope glycoprotein gene for Sindbis virus constructed by using MrBayes (http://mrbayes.sourceforge.net/). The phylogram includes 16 Sindbis virus strains isolated from mosquitoes collected in central......

Tables

• Table 1. Ornithophilic Culex and Culiseta spp. mosquitoes collected for the detection of Sindbis virus, central Sweden, 2009
• Table 2. Summary of 16 Sindbis virus isolates from ornithophilic Culex and Culiseta species mosquitoes collected in central Sweden, 2009

Suggested citation for this article: Hesson JC, Verner-Carlsson J, Larsson A, Ahmed R, Lundkvist A, Lundström JO. Culex torrentium mosquito role as major enzootic vector defined by rate of Sindbis virus infection, Sweden, 2009. Emerg Infect Dis. 2015 May [date cited].http://dx.doi.org/10.3201/eid2105.141577

DOI: 10.3201/eid2105.141577