Characterization of East London Culex pipiens s.l. in relation to the risk of transmission to humans of the West Nile virus in Great Britain.

Abstract

Concerns that West Nile Virus (WNV) may arrive in the UK, prompted investigations of Cx. pipiens s.l., as this species complex has been most often implicated in European urban WNV human outbreaks and the rapid spread of the virus across North America from 1999. Two members of the complex are present in Britain, Cx. p. pipiens and Cx. p. molestus. These distinct biotypes do not interbreed and are respectively ornithophilic and anthropophilic. Across Europe, these traits vary with latitude, presenting a major taxonomic problem. Research was conducted in an urban area of East London in and around the Beckton Sewage Treatment Works (STW), where Cx. p. molestus was a nuisance. Most of the study was conducted using a DNA based assay to distinguish the forms, which was first fully evaluated against the typical characteristics normally used for identification Temporal and spatial surveys of larval breeding sites indicated that Cx. p. molestus breeds all year round inside artificial enclosures both above and below ground in a range of both contained and non-contained pools varying widely in size, depth and water quality. Cx. p. molestus larvae were not found outside of enclourses even in the summer. However, adults were found biting humans. Hence, Cx. p. molestus appears to move from the Beckton STW to obtain its blood meals and returns. Despite a search of all samples no hybrids were found. The two biotypes did not seem to form hybrids confirming them as essentially separated. The biting specificity of the two biotypes was studied in an urban farm where human, animals and birds live in close contact. While Cx. p. pipiens was found to be exclusively ornithophilic, Cx. p. molestus resulted to be anthropophilic and capable to take 5.5% of its blood meals from birds, thus being a potential bridge vector for the transmission of the WNV to humans in Britain.