Viewpoint: Contracting TB from your pet

From l to r: Nicholas Lockwood, Prof Simon Maskell, Dr Alex Phillips and Andre Finn.

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Malcolm Bennett is Professor of Veterinary Pathology in the University of Liverpool’s Institute of Infection and Global Health

“The bacterial species that causes bovine TB, Mycobacterium bovis, is part of a closely related group of bacteria that, in Britain, includes the agents causing human TB and vole TB.  While mainly circulating in cattle, people and voles respectively, all can infect a wide range of mammals including humans.

“In the 19th and early 20th Centuries, bovine TB was relatively common in people, who contracted it from drinking milk: nowadays it is relatively rare owing both to control of the disease in cattle and, particularly, the pasteurisation of milk, a heat treatment that kills the bacteria. Control in cattle was based on testing and culling.

“The re-emergence of bovine TB in cattle in recent decades is complicated by the involvement of wild badgers in the ecology of the infection: controlling the spread of the disease in cattle is hard enough, but control of any infection in wildlife is notoriously more difficult still and the means of doing so, certainly in the case of badgers and TB, politically contentious.

”It is difficult to imagine direct contact between all these cats and either cattle or badgers – perhaps another, transient, wildlife host was involved, perhaps there was a shared contaminated environment, or perhaps there was some cat-to-cat transmission”
”Occasional cases of TB in pets have always been seen – often human TB in dogs, probably caught from their owners, and vole TB in cats, presumably caught through hunting wild rodents. There seems to be an increase in the number of cases of bovine TB diagnosed in cats in recent years, and the report from Public Health England (PHE) and the Animal Health and Veterinary Laboratories Agency (AHVLA) describing a cluster of feline cases and associated human infections emphasises both the wide host range of these bacteria and how sharing our lives with other animals, whatever the benefits, carries some risk. However, human infection, feline infection and transmission between the two remain rare.

“This cluster of feline cases and spill-over into their owners may reflect the expanding epidemic of bovine TB in cattle and wildlife, but it is unclear precisely how the cats involved became infected in the first place. It is difficult to imagine direct contact between all these cats and either cattle or badgers – perhaps another, transient, wildlife host was involved, perhaps there was a shared contaminated environment, or perhaps there was some cat-to-cat transmission.

“Whatever the initial route, however, these cases provide a reminder to vets that tuberculosis can occur in pets and put their owners at risk, and to doctors that not all human TB is caught from other humans. Given that treatment of cats and dogs requires lengthy use of special antibiotics and is seldom successful, the risk of transmission to owners and other animals probably means that euthanasia is the sensible option once a diagnosis is made.  Doubtless this report will also, through raising awareness, lead to further cases being diagnosed, and we will have to take care not to confuse increased diagnosis with increasing rates of infection.”

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