Image copyright SPL Image caption Scientists say something about the processed meat in English sausages allows the virus to stay alive

One in 10 sausages and processed pork meat products in England and Wales could cause hepatitis E virus (HEV) infection if undercooked, experts warn.

There has been an "abrupt rise" in the number of cases in England and Wales as people do not realise the risk, scientists advising the government say.

Sausages should be cooked for 20 minutes to reach 70C internally to kill the virus, they said.

Although serious cases are rare, HEV can cause liver damage or be fatal.

Official government figures show there were 124 confirmed cases of HEV in 2003, which rose to 691 cases in 2013. There were 461 cases in the first six months of this year.

Symptoms include jaundice and sometimes tiredness, fever, nausea, vomiting and abdominal pain.

Most people will get over the virus, although for some, such as those with an immune deficiency disorder, or pregnant women, it can prove fatal.

Prof Richard Tedder, at University College London (UCL), said HEV was "very common" in the UK - not all cases are noticed or recorded.

"This virus is taking off within the pig herds from which this country sources its processed pig meat in sausages and pork pies," he said.

Prof Tedder said sausages needed to be "caramelised" - cooked thoroughly - before eating to make sure they did not pose a health risk.

"It's a question of getting people to change," he said. "Everybody knows you can get salmonella from chicken."

However, he said, the figure of 1 in 10 sausages presenting a potential risk of hepatitis E infection if undercooked should be interpreted with caution.

"This figure was taken from a small survey (63 sausages), and is unlikely to be representative of the UK as a whole.

"Given what is known about the prevalence of high viraemia at the time of slaughter in the UK, a more representative figure would be about 1 in 100, or 1% of sausages, and any risk of infection can be alleviated by ensuring sausages are cooked thoroughly."

Infected water

He said the virus occurred in the animal and in the blood system and warned it would continue unless there was a "big change" in animal practices, such as introducing different hygiene measures.

Image copyright Thinkstock Image caption Hepatitis E can also be caught from strawberries irrigated with infected water

Dr Richard Bendall, at the Royal Cornwall Hospital Trust, said HEV was the most common virus passed on through animals in Britain.

He said the virus was found in 10% of sausages and processed pork meat.

This estimate comes from a study that looked at the pork production chain in the UK.

Dr Harry Dalton, also at the Royal Cornwall Hospital Trust, said the virus was not just confined to pigs, people had caught it from strawberries irrigated with infected water.

Shellfish in west Scotland and Tuscany had also infected people, he said.

In Asia and Africa, hepatitis E is more commonly transmitted by contaminated drinking water.