A species of mosquito capable of transmitting a disease called West Nile virus to humans has been discovered breeding in Britain for the first time since 1945.
Scientists who studied marshlands in southern Britain say they were able to record significant populations of the mosquito, known as Culex modestus, at several sites in the counties of Kent and Essex during 2010 and 2011.
West Nile virus mostly infects birds, but when it is transmitted from birds to humans by the bites of mosquitoes it can occasionally cause severe disease and sometimes kills.
It's not clear how long this species of mosquito has been in the UK, said Nick Golding of Britain's Oxford University and the Center for Ecology and Hydrology (CEH), who conducted the research.
It's not too worrying at the moment, but it's something to watch, he said in a telephone interview. He stressed that the although the mosquitoes have been found in Britain, the virus they carry has not yet been detected there.
A handful of Culex modestus were collected on the southern coast of Britain and recorded more than 60 years ago, but didn't appear then to be an established population. The species hadn't been seen again in Britain until now, said Golding, whose findings were published in the journal Parasites and Vectors.
He suggested the new population had arrived fairly recently, possibly via international shipping.
Disease surveillance experts suspect the Culex modestus species may be behind recent sporadic epidemics outbreaks of West Nile virus in southern Europe.
The virus, which survives in nature in a cycle involving transmission between birds and mosquitoes, is commonly found in Africa, the Middle East, North America and West Asia and can cause neurological disease and death in people.
Miles Nunn, a molecular parasitologist at CEH who reviewed the findings, said that in continental Europe Culex modestus mosquitoes are able to transmit West Nile virus because the virus can reproduce inside them, and then gets passed on when the mosquito feeds on both humans and birds.
However, in the UK the mosquitoes biting habits and ability to transmit West Nile virus have yet to be investigated.
Golding, Nunn and colleagues at the CEH, Britain's Health Protection Agency, and Oxford University said they are now conducting more studies to see how widespread the mosquitoes are and whether there is any risk to human health.
The Stockholm-based European Center for Disease Prevention and Control (ECDC), which monitors disease in the European Union, warned last year that West Nile virus might have established itself in parts of southern Europe.
The ECDC's latest surveillance report said that as of January 13, 96 confirmed human cases of West Nile virus had been reported in the EU, more than two-thirds of them in Greece and others in Hungary, Italy and Romania.
In 1999, a West Nile Virus strain circulating in Israel and Tunisia was imported into New York and led to an outbreak that spread through the United States in the following years.
The World Health Organization (WHO) says on its website that the U.S. outbreak, which lasted around 10 years, showed that importation and establishment of vector-borne pathogens outside their current habitat represent a serious danger to the world.