Let’s start with the facts about the cats with TB, as reported in the Vet Record: perhaps surprisingly, these have not been published in full in any of the mass media outlets in the past two days:
BETWEEN December 2012 and March 2013, a veterinary practice in Newbury (west Berkshire) diagnosed nine cases of Mycobacterium bovis infection in domestic cats. In seven of those cases the diagnosis was confirmed by bacteriological culture. The nine affected cats belonged to different households and six of them resided within a 250 metre radius. The animals presented with mycobacterial disease of variable severity including anorexia, non-healing or discharging infected wounds, evidence of pneumonia and different degrees of lymphadenopathy. The latest information is that six of the cats have been euthanased or have died. The three surviving animals are undergoing treatment and are reported to be responding. At the time of writing, no new cases had been detected in local cats since March 2013.
The newspapers have missed this aspect of the story, and focussed entirely on the fact that the disease, for the first time, seems to have been passed on to two humans who had been in contact with one of the cats. The humans have responded well to treatment.
Despite journalists’ suggestions that the cats could have picked up TB by “fighting badgers” (has anyone ever heard of this happening?), veterinary scientists believe that most cats are infected with TB when bitten by infected small rodents while hunting. These rodents in turn would have been infected by sniffing around infected badger setts. When a cat is diagnosed with TB, an owner has always been advised that treatment of the cat may be possible, but the remote chance of a human picking up TB from the cat is something that has to be taken into account when considering doing this. For this reason, many cats diagnosed with TB are euthanased. There is nothing new about any of this: vets have (rarely) been diagnosing TB in cats for many years.
The last sentence of the Vet Record report is worth repeating: here it is in capitals in case you missed it: NO NEW CASES HAVE BEEN DETECTED IN LOCAL CATS SINCE MARCH 2013.
From the media coverage, you would swear that this was an immediate and present threat to human life. The facts are far less exciting. Following the episode a year ago, due to the unusually high concentration of TB in cats in the area, all humans in contact with the affected cats were offered to be screened for TB. Of 39 people who were offered this, 24 accepted screening, and two people (who had contact with the same cat) were subsequently diagnosed with active TB disease caused by the same TB organism that had affected the cats. Only one person had been showing any symptoms of TB, and both are responding to treatment. Two other people had some broad evidence of exposure to TB, but there was no evidence to suggest that it was the same TB that had affected the cats.
To summarise: two people, over a year ago, were diagnosed with TB that was linked to a cat. Two other people were diagnosed with previous exposure to TB that may or may not have been linked to cats. Meanwhile, 8751 cases of human TB were reported in the UK in 2012, picked up from humans.
The message from today’s media seems to be: “DANGER: YOU COULD GET TB FROM CATS”.
The message that they should have given out is far less dramatic:
“The absence of reports of confirmed cat to human transmission of TB previously led public health practitioners to consider the risk of transmission as negligible. However, an assessment of this incident raised the risk of transmission of TB from cats to humans from negligible to very low.”
Or to put it more simply: Up till now, there was thought to be a minimal risk of picking up TB from cats. Based on an incident over a year ago in England, there’s now thought to be a very low risk.
But that wouldn’t make good headlines, would it?