Potentially deadly diseases like the West Nile virus are entering Britain, a leading expert has claimed.
Most of these diseases are spread by mosquitoes
Professor Ernest Gould, who works at the Centre for Ecology and Hydrology in Oxford, says he has found signs of these diseases in birds.
He carried out tests on 30 species across the country and found antibodies to deadly diseases in 50% of birds.
But Professor Gould said there was no evidence of any risk to animals or humans.
Exposed to disease
"We have found antibodies to West Nile virus, Usutu virus and Sindbis virus," he told BBC News Online.
"Infection in these birds was sub-clinical which means they were healthy but the antibodies suggest they have been exposed to these diseases."
West Nile virus is transmitted by mosquitoes which feed off birds with the disease. It is normally found in Africa but has recently emerged in the United States.
While most of those who contract the disease do not suffer illness, it can cause encephalitis, meningitis and death.
Usutu virus is also transmitted by mosquitoes. This disease has rarely been found outside Africa. However, an outbreak in Austria in 2001 killed thousands of birds. The risks to humans are unknown.
Sindbis virus was recently discovered in birds in Scandinavia. It can cause fever in humans and has been linked to a form of arthritis.
"These viruses are being moved by birds and mosquitoes," said Professor Gould. "They are probably coming into this country."
Professor Gould and colleagues at the Centre for Ecology and Hydrology are now carrying out further tests to see if there is any threat to people living in Britain.
"So far, no associated disease in humans has been identified. We don't have any evidence that is but that is not to say it isn't happening."
Professor Gould will tell the Society for General Microbiology that increased travel and
increasing urbanisation are helping to spread these diseases.
"We are being exposed more frequently to more viruses and this is because of increased movement. There is a risk."
The Health Protection Agency carries out checks on animals to see if they are carrying diseases that may pose a threat to humans.
A spokesman said: "Although there continues to be some concern over the theoretical possibility of human infection from West Nile virus in the UK, the risk of this is considered to be low and no endemic cases have ever been reported.
"However, the HPA carries out surveillance of infectious diseases all the time."
The Department of Health is drawing up plans to deal with any future outbreak of West Nile virus in the UK.
"This plan includes surveillance measures, testing procedures, travel and health education
advice and advice on effective methods of controlling the insect vectors of this virus," said a spokesman.
"All of the information in the strategy will be based on the
best advice available from both expert scientists and government advisory committees."