Government officials today warned that anyone with flu symptoms should stay away from pigs as evidence mounted that the present swine flu virus in humans could potentially infect the animals.

Vets and scientists have apparently demonstrated in an experiment at a UK research centre that the H1N1 virus responsible for the global pandemic in people readily transfers to the animals. Animal and public health specialists remain cautious about the consequences of their findings, which they describe as "preliminary", saying firm conclusions cannot be drawn.

Despite its name, there are no known cases of people infected in the present swine flu crisis catching the illness from pigs or other animals, but there has been a case in Canada where pigs are thought to have caught the flu from a carpenter returning from Mexico. However, swine flu is caused by a virus that usually infects pigs, and the animals are among those generally considered most likely to act as mixing vessels for different strains of flu that could turn into highly contagious diseases.

The experiment, a cross-EU venture conducted at the government's veterinary labs in Weybridge, Surrey, involved infecting a group of pigs with a virus strain from an infected person in North America. Early analysis of the experiment suggests not only that the pigs are susceptible to the virus but that it transmits to other pigs, the team reports in a letter to the Veterinary Record journal.

Defra, the government department responsible for the agricultural monitoring against swine flu in pigs, said: "These findings reinforce existing guidance to pig keepers (or anyone else coming into contact with pigs) that they should stay out of contact with pigs if they have flu-like symptoms and should continue to practise high levels of hygiene.

"There is no evidence that this strain of influenza virus is (otherwise) present in pigs in this country. We continue to take the situation very seriously and will maintain our surveillance effort, keeping the public and industry informed of any developments."