The hospital superbug MRSA has been found in pets for the first time in Britain, prompting fears that animals could infect their owners.

The discovery that the deadly bacteria have crossed the species barrier will make it harder to limit their spread and could make the common antibiotics used to treat infections far less effective.

MRSA (methicillin-resistant staphylococcus aureus), which kills 5,000 patients a year, is carried harmlessly by one in three people. But it can prove fatal in the elderly, those recovering from surgery and those who have a weakened immune system. Newborn babies are also susceptible.

In the last year, 12 animals were found to be carrying the bug by infection control experts at the Health Protection Agency in London, who had received veterinary samples from cats, dogs and a rabbit. The matter is being treated with urgency and an investigation is planned for the new year - although last night the British Veterinary Association urged the public not to panic and abandon their pets.

Angela Kearns, head of the staphylococcus research laboratory at the agency, said: 'We have observed MRSA in some domestic animals. We confirmed this in our laboratories. The cases came from across Britain so we know it's not one particular cluster.

'We need to know if there is a lot of it out there, what are the risks? We don't know yet whether animals have acquired the infection from humans or vice versa. There really is a big question mark over the whole area.'

Until now, hospitals have been seen as the major breeding-ground for MRSA. The discovery of the bug in animals raises the possibility of a battle on many fronts.

As with humans, animals can carry around the bacteria harmlessly and will only be at risk should they have an accident and need surgery or if they have an open wound.

MRSA was first reported in animals two years ago, with the discovery by Canadian microbiologist Dr Donald Low that an Irish thoroughbred had the bug. Since then, Low has confirmed cases in cats, dogs, guinea pigs and horses in the United States.

'This is a warning to Britain about MRSA,' said Low of the Mount Sinai hospital in Toronto, who believes the spread of MRSA in animals is, like its spread in hospitals, due to the use of the strong antibiotic quinoline instead of penicillin. 'I've looked at the case of a horse, a thoroughbred, which ended up infecting its owner. Horses are particularly at risk because they're expensive animals and vets tend to use expensive drugs on them.'

The British Veterinary Association urged pet owners not to start abandoning their pets. Spokesman Dr Alistair Gibson said: 'We don't want to see a massive scare that will make people get rid of their pets. What we need is for research to be done into this. Meanwhile, owners should take a sensible approach, wash their hands regularly and not panic.'