A fifth farm has partially closed following an outbreak of E.coli, the Health Protection Agency said today.
It advised Hambleton District Council that Big Sheep and Little Cow Farm in Bedale, North Yorkshire, should take action as a "precautionary measure".
Three cases of the O157 strain of the bug have potentially been linked to the farm, it said.
The attraction closed voluntarily and the Health Protection Agency (HPA) and its partners are now conducting "a full epidemiological investigation".
The agency said it was aware of a further five cases of E.coli O157 in people who had visited Big Sheep and Little Cow Farm.
But it said there is no confirmation that the site is the source of infection.
The farm has now stopped all tours and contact with the animals or their enclosures.
But a playbarn, which is said to be separate from these areas, remains open.
Four farms have already shut following the outbreak which came to light at Godstone Farm, near Redhill, in Surrey.
Dr Stephen Morton, Regional Director of the Health Protection Agency in Yorkshire and the Humber, said different types of the O157 bug had been linked to Big Sheep and Little Cow Farm.
"Where there are different types of E.coli O157 involved, as there are in this case, there is uncertainty about whether there is a shared source of infection," he said.
"Tests are ongoing to ascertain the types concerned in the latest three cases.
"The HPA has advised that all tours of the farm and contact with the animals or animal areas is closed on a precautionary basis to protect public health while the investigation continues."
According to the HPA, all those who have contracted the bug, including the three confirmed this week, are either well or recovering. None are in hospital.
The agency said: "There are many potential sources of E.coli and the majority of E.coli O157 outbreaks are caused either by food contamination or person to person spread and only about one in 50 of all cases are associated with outbreaks linked to petting farms."
Hambleton District Council said those infected by the bug were well or recovering at home.
A spokesman said animals had been removed from the farm and the petting area was being thoroughly cleaned.
A playbarn on the site - away from the animal area - remained open.
Maurice Cann, head of regulatory services at the council, said: "We are treating this case very seriously - the animals have now been moved away from the site and the petting area will be deep cleaned.
"E.coli O157 is very easily spread and can be extremely serious in young children and the elderly.
"We are primarily concerned with the health and safety of the visitors when we make recommendations as to the best course of action to take but we must also consider that this business is someone's livelihood.
"It was confirmed this week that three cases of E.coli O157 are potentially linked to the farm but there are another five cases in people who had visited Big Sheep and Little Cow, although there is no confirmation that the farm is the source of infection in these cases. All are either well or recovering at home."
The council said environmental health officers were working closely with the owner of the petting farm and said a series of improvements had been put in place.
A spokesman said facilities for hand washing were now better and signage had been improved. Further options were being explored.