Public health experts in the UK say transmission risk of cat-to-human TB infection is low, but recommend putting down cats confirmed to have the disease.
THE first documented evidence that TB can spread from cats to humans has been reported by public health officials, confirming long-held concerns about the disease’s capacity to jump from one of Britain’s favourite pets.
Public Health England (PHE) said a few days ago that the risk of the disease being transmitted from cats to people was very low. However, putting down cats confirmed to have TB was the most sensible course of action because people having close contact with them faced a potentially significant risk of infection, it said.
Two people were found to have developed active TB after close contact with cats last year following an outbreak involving nine animals in west Berkshire and Hampshire.
They are said to be responding to treatment.
Two other people were found to have latent TB, meaning they had been exposed to the disease at some point but it was not active.
The risk of the spread of TB from cats to humans had previously been regarded by UK advisers as negligible despite the potential for transmission being recognised after years of serious outbreaks in cattle, which have led to controversial badger culls.
The outbreak of the disease in cats, caused by a strain known as Mycobacterium bovis (M. bovis), came to light via a veterinary practice, and led to screening being offered to 39 people, 24 of whom accepted. Six of the nine cats were put down, three were treated.
The head of gastrointestinal, emerging and zoonotic diseases at PHE, Dilys Morgan, said: “It’s important to remember that this was a very unusual cluster of TB in domestic cats. M. bovis is still uncommon in cats – it mainly affects livestock animals.
“These are the first documented cases of cat-to-human transmission, and so although PHE has assessed the risk of people catching this infection from infected cats as being very low, we are recommending that household and close contacts of cats with confirmed M. bovis infection should be assessed and receive public health advice.”
Molecular analysis at the government’s Animal Health and Veterinary Laboratories Agency (AVHLA) showed that M. bovis isolated from the infected cats and the people with active TB were indistinguishable, indicating transmission of the bacterium from an infected cat.
In the cases of latent TB, it has not been possible to confirm the source of their exposure or whether they were caused by M. bovis.
Transmission of M. bovis from infected animals to humans can occur by inhaling or ingesting bacteria shed by the animal or through contamination of unprotected cuts in the skin while handling infected animals or their carcasses.
The head of the bovine TB genotyping group at AHVLA, Noel Smith, said: “Testing of nearby herds revealed a small number of infected cattle with the same strain of M. bovis as the cats.
However, direct contact of the cats with these cattle was unlikely considering their roaming ranges. The most likely source of infection is infected wildlife, but cat-to-cat transmission cannot be ruled out.”
Cattle herds with confirmed cases of bovine TB in the area have all been placed under movement restrictions to prevent the spread of disease. Experts are said to be on the lookout for further cases of disease caused by M. bovis in humans, cats or any other pet and livestock animal species.
In the 1930s, TB caused by M. bovis killed 2,500 people a year and infected 50,000, but now the route is diagnosed in fewer than 40 Britons a year, mostly in over-65s through reactivation of latent infection dating from before the introduction of hygiene controls, including routine milk pasteurisation.
This accounts for less than 1% of all diagnosed TB cases in the country, and those who work closely with livestock and/or drink unpasteurised milk are most at risk.
Fewer than 30 cats in Britain were identified as having TB between 2006 and 2012, although research from Edinburgh University last year suggested far more cats developed the disease than had previously been thought.
The government’s cross-UK Human Animal Infections and Risk Surveillance group (Hairs) also considers present figures to be underestimated. Incidents usually happen where TB is endemic in cattle and wildlife.
The Berkshire/Hampshire outbreak, involving seven confirmed and two suspected cases between December 2012 and March 2013, has taken time to report because of the detailed investigations necessary.
The nine cats belonged to nine separate homes, six of them within 250 metres of each other. Seven cases matched a distinct M. bovis strain, detected in cattle in the area in 2008.
All the cats had severe systemic infection. Some had non-healing or discharging wounds, or a recent history of bites. – Guardian News & Media