The Animal Health and Veterinary Laboratories Agency (AHVLA) and Public Health England (PHE) have announced that two people in England developed tuberculosis after contact with a cat infected with Mycobacterium bovis, the cause of TB in cattle.

According to the AHVLA, nine cases of M bovis infection in domestic cats in Berkshire and Hampshire were investigated by AHVLA and PHE during 2013. The latter offered TB screening to 39 people identified as having had contact with the infected cats as a precautionary measure, and 24 contacts accepted.

Following further investigations, two cases of active TB and two cases of latent TB (exposed at some point, but not suffering from active disease) were identified. Both cases of active TB disease confirmed infection with M bovis and are now responding to treatment. No further cases of TB in cats have been reported in Berkshire or Hampshire since March 2013 and PHE has assessed the risk of transmission of M bovis from cats to humans as being “very low“.

Head of gastrointestinal, emerging and zoonotic diseases department at PHE Dilys Morgan said the cases came from a “very unusual” cluster of TB in domestic cats.  

M bovis is still uncommon in cats – it mainly affects livestock animals,” she said. “These are the first documented cases of cat-to-human transmission, so although PHE has assessed the risk of people catching this infection from infected cats as being very low, we are recommending household and close contacts of cats with confirmed M bovis infection should be assessed and receive public health advice.”

Molecular analysis at AHVLA showed M bovis isolated from the infected cats and the human cases with active TB infection were indistinguishable, indicating transmission of the bacterium from an infected cat. In the other cases of latent TB infection, it was not possible to confirm whether they were caused by M bovis or what the source of exposure was.

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 carcases.

Noel Smith, head of the bovine TB genotyping group at the AHVLA, said testing of nearby herds revealed a small number of infected cattle with the same strain of M bovis as the cats, but 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,” he said.

Cattle herds with confirmed cases of bovine TB in the area have all been placed under movement restrictions to prevent the spread of disease.

Local human and animal health professionals, meanwhile, are remaining vigilant for the occurrence of any further cases of disease caused by M bovis in humans, cats or any other pet and livestock animal species.

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