1 in 100 cats are infected with toxoplasma / Rex Features

Agency also attacked for failing to warn of risk of contamination from eating undercooked lamb

The Food Standards Agency (FSA) is going to review its advice to pregnant women and other groups of people who could be at risk of health problems as a result of being infected with toxoplasma, a microscopic parasite carried by cats and transmitted in contaminated food.

The Independent revealed yesterday that toxoplasma is infecting up to 1,000 new people a day in Britain – about 350,000 people a year – and that it has been tentatively linked with mental impairment as well as the known serious health problems of congenital birth defects, blindness and dementia.

The FSA will detail later this year how it intends to amend its existing advice to vulnerable groups. Its advice currently states that pregnant women and patients with compromised immune systems should avoid cat litter and eating rare meat, which can harbour toxoplasma cysts. Although most people infected with toxoplasma show no obvious symptoms, there is growing evidence that the parasite may cause behavioural changes, ranging from increased risk taking and delayed reaction times to schizophrenia.

The FSA's chief scientist, Andrew Wadge, said that a report by the FSA's Advisory Committee on the Microbiological Safety of Food found that further research is needed to establish how toxoplasma is spreading to people from cats.

"This thorough and detailed report points out key gaps in our knowledge about this parasite and suggests areas where more research is needed which will help us in estimating how much infection is due to food and which foods might be the highest risk," Dr Wadge said.

"The report also suggests we look again at our advice to vulnerable groups and ensure that it reflects current scientific knowledge. We're going to look carefully at the report's recommendations and will publish a response in due course."

Experts called yesterday for more to be done to warn the general public about the risks posed by toxoplasma and some have warned people against eating undercooked meat, especially lamb, which is thought to be at high risk of being contaminated.

Barbara Lund, a microbiologist at the Institute of Food Research in Norwich, said that she would not advise people to eat rare lamb and criticised the FSA for saying that it is perfectly safe for most people to eat pink meat provided it is cooked on the outside. "Regarding the comment that it is safe to serve whole cuts of beef and lamb rare as long as they have been properly cooked on the outside, it is not clear to me that we can be confident of this advice for sheep meat," Dr Lund said.

Fuller Torrey, an expert on schizophrenia and toxoplasma at America's Stanley Medical Research Institute in Maryland, said that the seriousness of the potential risks posed by the parasite to the general public means that all meat should be cooked thoroughly to kill parasitic cysts lying dormant within muscle tissue.

"Eating any meat that is rare or undercooked is not safe. I would not advise anyone to eat undercooked meat given what we know and don't know about this organism," Dr Torrey said.

But Sarah O'Brien, who chairs the Advisory Committee on the Microbiological Safety of Food, said yesterday that although more work needs to be done to understand how toxoplasma is entering the food chain, there is no need at present for people to avoid eating rare meat unless they are pregnant women or immune-compromised patients.

"There is no evidence to suggest that people generally should change their eating habits, and I think the FSA is right to say that most of the population can continue to enjoy lamb and beef cooked rare," Dr O'Brien said.

Beth Skillings, clinical veterinary officer for the charity Cats Protection, said that while cats are the definitive host for toxoplasma, contact with cats is not a risk for infection: "Even vets are no more likely to be infected with the parasite than non-vets. Most people contract toxoplasmosis through other routes such as eating undercooked meat, inadvertently ingesting contaminated soil through gardening or eating unwashed vegetables."

Toxoplasma in numbers

1 in 100 Cats infected with toxoplasma.

3 Babies in every 100,000 are born with toxoplasmosis in the UK.

People infected with the toxoplasma parasite are 2.7 babies in every 100,000 are born with toxoplasmosis in the UK.