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Bovine tuberculosis in cats
  1. Bob Monies1,
  2. Keith Jahans2 and
  3. Ricardo de la Rua3
  1. 1VLA – Truro, Polwhele, Truro, Cornwall TR4 9AD
  2. 2VLA – Weybridge, New Haw, Addlestone, Surrey KT15 3NB
  3. 3Tuberculosis Division, Animal Health and Welfare Directorate General, DEFRA, 1A Page Street, London SW1P 4PQ

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SIR, – The occurrence of bovine tuberculosis (TB) in cats is well documented (Wilesmith and Clifton-Hadley 1994, Gunn-Moore and Shaw 1997), and the possibility that TB in cats is the result of transmission of Mycobacterium bovis infection from wildlife or cattle has been considered previously (Monies and others 2000). Between 1980 and 2003, M bovis was isolated from cats on 41 occasions at the Veterinary Laboratories Agency (VLA). Before 2004, in a typical year fewer than 15 cat samples would be submitted to the VLA for mycobacterial culture. Impending changes to the existing animal TB legislation, the provision of free bacteriological testing for TB at the VLA and better liaison with feline veterinary interests has resulted in a significant increase in the numbers of samples submitted to the VLA for TB culture. We would like to report the findings of 98 samples from cats received for mycobacterial culture at the VLA during 2005.

M bovis was isolated on 12 occasions, Mycobacterium microti was isolated on nine occasions,Mycobacterium avium was isolated on four occasions,Mycobacterium malmoense was isolated on one occasion, as was Mycobacterium celatum, and on two occasions an unclassified mycobacterium was isolated. At the time of writing, cultures for mycobacteria have yet to be completed for nine of the samples.

Of the 12 cases of M bovis infection in cats, clinical histories indicated that six of these first presented with a discharging granulomatous abscess or bite wound and, of these, three also developed respiratory signs. Four of the 12 cases presented as mycobacterial conjunctivitis (with or without an associated injury to the eye), and of the two remaining cases one presented with an abdominal mass and the other presented with an enlarged submandibular lymph node.

To our knowledge, seven of the 12 cases have been euthanased to date and five have been treated and are reported to be clinically recovering. Seven of the 12 cases originated from households with more than one cat, and in these any remaining cats have been reported to be in good health. In all cases of confirmed M bovis infection, a veterinary officer of the State Veterinary Service (SVS) informed the relevant consultant in communicable disease control of the Health Protection Agency of the findings and advised the cat owners and their private veterinary surgeons of the associated animal and public health risks.

All 12 cases were in cats from rural areas of England and Wales in which there is a recognised incidence of TB in cattle and badgers. The 12 M bovis isolates included nine different spoligotypes, and for each of the 12 affected cats the spoligotype was the same as the predominant spoligotype historically found in cattle and badgers in the area from which they originated.The owners of five of the cats specifically referred to a knowledge of badgers visiting their garden or a knowledge of a badger sett in close proximity to their garden. One owner referred to an unusually high population of polecats in the vicinity of their home, and another owner reported wild deer in close proximity to their garden.

The evidence would suggest that cats become infected by exposure to infectious material from tuberculous cattle or badgers (or other maintenance hosts of M bovis). Cats are therefore considered spillover hosts of M bovis and, indeed, removal of the source of infection in cattle or wildlife would be expected to result in a reduction in the incidence of bovine TB in cats. However, cats are not true end hosts, as the disease presentation makes them (at least theoretically) capable of infecting other cats and other mammals, including humans. For this reason, when making a decision on whether to treat a confirmed case of M bovis infection in a cat, a careful assessment of the zoonotic risk and the potential for transmission to other pets in the household should be made, not to mention all the practical problems and financial costs involved in the proper and complete treatment of TB in animals.

Finally, we wish to take this opportunity to remind colleagues that a new Tuberculosis (England) Order (as amended) will be coming into force on February 20, 2006. This Order, and similar Statutory Instruments in Wales and Scotland, will retain the current legal obligation to notify the suspicion of TB in cattle and deer. In addition, the new Orders will include provisions whereby the detection of tuberculous lesions in carcases of farmed mammals or mammals kept as pets will become notifiable to the Divisional Veterinary Manager.Under the new Orders it will also be compulsory to notify the VLA if M bovis is identified by laboratory examination of samples taken from a mammal (other than humans), unless the organism was present in the sample as part of an agreed research programme. Notification of suspicious TB lesions in a living pet at surgery by radiography or biopsy will not be covered in the Order, but referral of clinical or pathological material from such cases to the VLA is to be encouraged. The SVS and VLA regional laboratories will continue to facilitate the submission of tissue specimens to the VLA – Weybridge for mycobacterial culture at DEFRA’s expense.

Bacteriological culture is the only available method to confirm a presumptive diagnosis of M bovis infection. Therefore, veterinary practices and referral laboratories should submit the whole carcase to the nearest VLA regional laboratory. Fresh (unfixed) tissue samples or a swab should be sent directly to the TB Diagnosis Laboratory at VLA – Weybridge. Any material submitted should be accompanied by a full case history as well as the name, address and postcode of the owner.

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