Two people have caught tuberculosis after contact with infected cats, public health experts have warned.
It is the first time that TB has been transmitted from cats to humans.
Public Health England (PHE) and the Animal Health and Veterinary Laboratories Agency (AHVLA) investigated an outbreak of TB in nine cats in Berkshire and Hampshire last year.
As a precaution, 39 people who had been in close contact with the animals, were offered TB screening.
Two were found to have the active disease with exactly the same strain of Mycobacterium bovis carried by the cats.
Another two had 'latent' disease, meaning they had been exposed to the bug at some point in the past.
No further cases of TB in cats have been reported in Berkshire and Hampshire since March 2013.
Both confirmed cases are responding to treatment.
Dr Dilys Morgan, of PHE, said the risk of transmission to humans is "very low".
She 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."
Symptoms of TB in cats include coughing, wheezing and weight loss. There may also be lumps, abscesses or bite wounds that fail to heal, particularly around the head and neck.
The disease can be transmitted by inhaling or ingesting bacteria shed by infected cats, or through contamination of unprotected cuts.
Professor Noel Smith, of the AHVLA, 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.
The findings of the animal health aspects of this investigation are published in The Veterinary Record.