London - A parasite spread by cats is infecting 1,000 new people every day in Britain - about 350,000 a year - according to an official assessment of the risks posed by toxoplasma, which can cause serious illness and has been tentatively linked with schizophrenia and other psychotic disturbances.
In news that will challenge public perceptions about the country's most popular pet, official figures to be published later this week will reveal the shocking levels of infection within the UK human population of Toxoplasma gondii, a microscopic parasite that forms cysts in the human brain and other vital organs of the body.
Toxoplasma infections come either through direct contact with cats or from eating contaminated meat or vegetables, tests on British blood donors have revealed.
Although the clinical signs can be mild, risk groups, such as pregnant women and patients with compromised immune systems, can suffer very serious side-effects, leading to congenital birth deformities, blindness, dementia and even death.
The true scale of the hidden problem has shocked experts who believe not enough is being done to warn the public of the known risks posed by toxoplasma, which they judge to be one of the worst food-borne illnesses because of the severity of its effects.
Some experts are calling cfor the condition to be made a notifiable disease in England and Wales - meaning that medical staff must be put on alert - bringing the two countries on a par with Scotland, where infections must be reported on a national database. Others question whether families with young children should have pet cats, while some say advice on cooking lamb and preparing vegetables should be changed.
In addition to infections caused by direct contact with cats, people can pick up the parasite by eating the meat of infected animals or from raw vegetables that have not been washed properly to rid them of any toxoplasma eggs contaminating the soil.
About 80 percent of infected people show no obvious symptoms of toxoplasma and are completely unaware that they are harbouring the parasite. However, new estimates suggest that up to 70,000 people a year in the UK develop some kind of symptoms.
Experts are especially concerned about the emerging scientific evidence suggesting that apparently healthy people with toxoplasma may still be affected unwittingly by the parasite, even when they show no obvious clinical symptoms.
A number of small-scale studies suggest that toxoplasma infection may alter people's personality, making them more prone to risk-taking or delayed reaction times. Studies have also linked toxoplasma infection to psychotic disturbances such as self-harm and suicide, and to serious psychiatric illnesses such as schizophrenia.
This week the Food Standards Agency (FSA) will publish a “risk profile” of toxoplasma in the food chain, The Independent has learnt. The group of experts commissioned to write the report estimates 350,000 new toxoplasma infections occur each year in the UK, most of them probably from eating contaminated food.
Experts have urged the FSA to review its advice to pregnant women and immune-compromised patients, and strongly advised it to change its policy stating it is safe for people to eat rare lamb.
Sheep are thought to pick up the parasite by eating pasture grass or concentrated feed that is contaminated with cat faeces. Preliminary studies indicate that nearly 70 percent of British sheep have been exposed to the feline parasite.
Pregnant women and patients with compromised immune systems are already warned to avoid pink meat.
One study found that two-thirds of lamb samples from a Manchester butcher tested positive for toxoplasma, but the FSA's chief scientist, Andrew Wadge, said that it is safe for people to serve lamb rare: “People traditionally eat and enjoy lamb cooked rare. For most people that is perfectly safe. Our advice is on the basis of what we know. I'm not going to tell you about the safety of lamb based on another five or 10 years of research.”
However, other experts disagree, warning that toxoplasma cysts in lamb muscle tissue can survive cooking when meat is served pink. “I would certainly not recommend eating rare lamb,” said Barbara Lund, a microbiologist at the Institute of Food Research in Norwich.
Fuller Torrey, an expert on schizophrenia and toxoplasma at America's Stanley Medical Research Institute in Maryland, said all meat should be cooked thoroughly to kill parasitic cysts lying dormant within muscle tissue because of the severity of the potential risks posed by the parasite.
“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.
Richard Holliman, a consultant medical microbiologist at St George's Hospital in London, who chaired the FSA's working group on toxoplasma, said that, based on existing scientific evidence, it is not yet justified to change the official advice on the safety of eating rare lamb for the general public.
Dr Holliman added: “Toxoplasma is more important, or as important, as salmonella and campylobacter, which affect a lot of people. Toxoplasma affects a few people but when it does affect them it can be devastating. A child born with congenital toxoplasma is damaged for life.”
EIGHT MILLION CATS, 800 BILLION EGGS - HOW THE DISEASE TAKES ROOT
The microscopic parasite Toxoplasma gondii is small enough to get inside the cells of the animals it infects. A single-celled organism known as a protozoan, it has a complicated life cycle involving rodents and cats. Toxoplasma can also infect humans and farm animals, but these species are accidental hosts.
The parasite can only reproduce sexually and form eggs within cats, which can shed millions of toxoplasma “oocysts” in their faeces. Cats become infected if they eat contaminated raw meat, or catch and eat infected mice or rats.
Cats can shed up to 10 million oocysts a day for up to 14 days after they become infected. There are 8 million pet cats in Britain and one percent are shedding toxoplasma oocysts at any one time; so there are in the region of 800 billion toxoplasma eggs being released each day. Toxoplasma oocysts in the soil remain viable for several years where they can be ingested by other animals which become infected with tissue cysts in their vital organs. Lamb meat has been shown from limited testing to carry the greatest risk of toxoplasma based on past exposure to the parasite by farm animals.
Fuller Torrey, director of the Stanley Medical Research Institute in Maryland, carried out studies of playground sandpits left uncovered at night. “I've just been looking at the data on levels of oocysts secreted by cats and I'm frankly appalled at the level of contamination of areas where they go to the bathroom,” Dr Torrey said.
“I estimated in some of these public sandboxes there are about a million viable oocysts per square foot of sand. I would not let any children of mine play in a sandbox that had not been covered at all times when not in use.”
Dr Torrey said he would go as far as to recommend against having cats as pets if there are young children in a household: “I would certainly advise families not to get a cat if they have small children. I gave this advice to my own daughter and granddaughter.”
An estimated 10 to 20 percent of infected individuals develop flu-like symptoms. The latent stage of toxoplasma can develop into serious illness when people become immune-compromised, for instance when undergoing some cancer treatments. One notable manifestation in immune-compromised patients is toxoplasmic encephalitis of the brain, which can be lethal.
If women become infected while pregnant, the parasite can damage the development of their baby in the womb, leading to miscarriage or congenital birth problems. - The Independent