A species of mosquito not seen in the UK since 1945 has been discovered breeding in the country. Populations of the mosquito, found across mainland Europe and known only by its Latin name Culex modestus, were recorded at sites in the marshes of north Kent and south Essex in 2010 and 2011.Culex modestus mosquito Photo © Institute for Animal Health

The discovery was made by postgraduate student Nick Golding, and the mosquito was definitively identified by colleague Stefanie Schäfer of the Centre for Ecology & Hydrology (CEH). The mosquito was also concurrently found by medical entomologists at the Health Protection Agency as part of their nationwide mosquito surveillance programme. Details of a collaborative study between CEH and the HPA are published today (9 February 2012) in the journal Parasites and Vectors.

Culex modestus is suspected to transmit West Nile virus (WNV) to humans during sporadic epidemics in southern Europe. However, to date, WNV has never been found in the UK so there is no known current risk to humans living here. The virus primarily infects birds, but when the pathogen is transmitted from birds to humans by the bite of a mosquito it can very occasionally cause severe disease, although it usually causes only asymptomatic or mild infections.

Lead author Nick Golding said, “It is unclear how long Culex modestus has been breeding in the UK – the new specimens were found during field studies in 2010 and 2011 – but it seems likely that the species has arrived fairly recently. A handful of individuals were collected on the south coast in the 1940s, but didn’t appear to be an established population. Since those records the species hasn’t been seen again in the UK, until now.”

Dr Miles Nunn from the Centre for Ecology & Hydrology, who is Nick Golding’s doctoral supervisor, said, “Not all mosquito species can transmit West Nile virus to people. In continental Europe, Culex modestus is able to because the virus can reproduce inside the mosquito and the mosquito feeds on both humans and on birds which are the main host of West Nile virus. Once the mosquito’s salivary glands become infected the virus is secreted into the host (man or bird) in saliva when the mosquito feeds. However, in the UK the mosquitoes' biting habits and ability to transmit West Nile virus have yet to be investigated.”

Nick Golding, Dr Nunn and colleagues at CEH, the HPA and Oxford University are continuing to work together to establish just how widespread these mosquitoes are and whether there is any risk to human health. They have been using satellite imagery in order to identify habitats where the mosquito might be breeding, before looking for it on the ground.

Nick is also studying Culex modestus and other mosquitoes to determine the specific habitat within the marshes in which they breed and what effect wetland management has on this habitat.

Dr Nunn added, “Culex modestus is difficult to distinguish from related mosquitoes that are less likely to transmit viruses to humans. Its discovery highlights the importance of expert long-term biological recording of UK wildlife by the scientific community.”

Additional information

A Q&A feature provides more background information on both Culex modestus and West Nile Virus

CEH issued a press release for this story.

The full paper "West Nile virus vector Culex modestus established in southern England" by Nick Golding, Miles A Nunn, Jolyon M Medlock, Bethan V Purse, Alexander G C Vaux and Stefanie M Schäfer is published in Parasites and Vectors.

Related CEH links

CEH Biodiversity Objective 2.2: The impact of invasive species, pathogens and vectors of disease





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