Britons might be catching hepatitis from pigs, a hypothesis that could undermine hopes of eventually using pigs' organs to cut waiting lists for human transplants, it emerged yesterday.

Vets investigating the prevalence of the hepatitis E virus in British herds found its signature looked like a strain identified in a human.The disease is rare in Britain, most of the 30 to 40 cases a year being people who have travelled to developing countries where hygiene is poorer. It is often endemic in pig herds in such countries.

It is usually mild compared with hepatitis B and C, which can lead to chronic disease, but it can cause severe liver failure in pregnant women.

Researchers from the government's Veterinary Laboratories Agency, writing in the Veterinary Record, have warned that the disease, which seems to have been well established in pigs for a decade, might on rare occasions leap from animals to humans. Pigs appear to carry the virus without symptoms and many humans may be carriers too, so hepatitis E might be more widespread than clinical cases suggest.

Xenotransplantation, using animal organs in humans, is still some years away but experiments between animal species have been attempted for some time. Pig cells may help cure diabetes, if experi ments using monkeys are any guide, while scientists have tried to transplant piglets' hearts to baboons.

But there have long been fears that diseases harmless to pigs might turn into killer viruses when transferred to humans, undermining hopes that humans could soon have life-saving heart, liver or kidney transplants from specially bred GM pigs. No near-human trials are even near development in Britain.

The virus found in young pigs from farms in Bedfordshire and Suffolk was very like that found in a patient from Cornwall who had not travelled outside Britain for more than four years, according to yesterday's report. "Further work is needed to establish more precisely the extent and impact, if any, of infection in pigs and people in the UK and other countries," it said.

But "limited data" so far suggested transmission between species could not be ruled out. The presence of such potential animal-to-human viruses "also has implications in the field of xenotransplantation."

· Tests for a bat form of rabies suggest it may occur more often than previously thought. In parts of Scotland one in 12 may have been exposed to the disease, while across Britain one in 50 bats may carry antibodies, though not necessarily infecting animals or people. A conservation volunteer died from bat rabies in 2002, one of only four confirmed human deaths in Europe in more than 25 years.