Parents were warned not to take young children on to working farms with livestock this weekend because of the risk of being infected with the O157 strain of E. coli bacteria.
Hugh Pennington, professor of bacteriology at the University of Aberdeen, said that children under five were at the highest risk of the serious and life-threatening complications that can arise from E. coli infections. He said that many farmyard animals, especially cattle, were carriers of the deadly O157 strain and small children were particularly vulnerable to being infected through contaminated manure.
Professor Pennington said it was not easy to supervise children under five when visiting a farm and it was relatively easy for them to touch animals orobjects that are smeared with manure and then put their hands to their mouths.
"If you take children under five they have to be heavily supervised and hand-held all the time because on the one hand they are more likely to get the complications from E. coli O1571 and on the other they are more difficult to control when they are toddlers," the professor said.
E. coli infections in very young children can quickly cause damage to kidneys and the brain for which there is no effective treatment. "If they get infected there is very little we can do to stop the complications happening," he said.
In January, the family of a six-year-old boy who was left severely brain damaged after contracting the bug during a visit to a Hertfordshire farm settled out of court with the farm.
Professor Pennington said infection was rare, but when it did occur, "the roof can fall in". "It's an unusual bug in that it can lead to complications that can have a permanent, damaging effect," he said. "It's a bit like meningitis. It's a rare infection but prevention is the name of the game. Once you've got it, you're in the lap of the gods as far as recovery is concerned because medical treatment does not really affect the success of dealing with these medical complications."
Professor Pennington is a world authority on E. coli O157 and led the government inquiry into the outbreak in Lanarkshire, central Scotland, which in 1996-97 claimed the lives of 21 people infected through eating contaminated meat.
He told The Independent that although the risks associated with visiting farms might be small, the consequences of being infected are so serious that many parents of young children should consider avoiding farms altogether. "It does boil down to a relative risk, andthe risk is small but it can be catastrophic. It's balancing an uncommon event because many people visit farms and only a few get infected. However, it is there as a real risk and the consequences can be lethal or lead to lifelong problems, such as brain or kidney damage," he said.
Although normal strains of E. coli are perfectly harmless, the O157 strain produces a highly dangerous toxin. The strain was first identified in the United States in the Seventies and appeared in Britain a few years later, where it has spread rapidly to cause more than 1,300 cases of human food poisoning a year.
"I have been involved in one or two high-profile cases where kids have been permanently damaged, which is maybe partly why I'm taking kind of a hard line on this," Professor Pennington said. "Until we can get better ways of preventing the complications, we really do have to concentrate on prevention and this seems a fairly logical way of doing it."
The professor said that children's zoos and ornamental farms where only small animals such as ducks, chickens and rabbits can be touched were not in the same league as a working farm with a milking herd. Chicken and ducks do not carry the O157 strain and although they can be infected with salmonella, it is less easy for this microbe to be transmitted and even if it does, any resulting illness is far less serious.
"All the evidence to date suggests that direct contact with animals, such as patting them, is a particular risk. Young calves are the highest risk animals," Professor Pennington said.
"Just going into the country itself is nowhere near as important a risk factor as going on to a farm and coming into contact with these particular animals. It all comes down to getting manure on your hands, basically, and putting hands into your mouth."
It is possible to control older children and make sure they wash their hands with warm water and soap but younger children pose a far more difficult problem of supervision.