British health officials announced today that two people have developed active tuberculosis (TB) after interacting with TB-infected cats, reports The Guardian. Two other humans were also infected, but the disease is not currently active. This is the first documented instance of cat-to-human TB transmission.

According to Public Health England, the transmissions occurred in the aftermath of a small outbreak involving nine felines who lived within 820 feet of each other. The outbreak was detected by a veterinarian, and health officials say that the strain was genetically identical in both the infected cats and the humans.

So far, the two people with active TB appear to be responding well to treatment. But six of the nine cats were put down. Dilys Morgan, a zoonotic disease expert at Public Health England, told The Guardian that "it's important to remember that this was a very unusual cluster of TB in domestic cats," adding that the particular strain that infected the cats, Mycobacterium bovis, is usually found in livestock.

Modern cases of TB in humans are rare. When they do occur, they usually happen because a strain is reactivated in someone who was infected before hygiene practices were widespread, The Guardian reports. But when TB does infect humans, it can be deadly. In the 1930s, M. bovis infected over 50,000 people each year, and killed about 2,500. Between 2006 and 2012, however, there were only 30 cases of cat TB in the UK, so the risk of thousands of folks being infected by way of feline contact remains fairly small.