Feline tuberculosis caused by Mycobacterium bovis infection of domestic UK cats associated with feeding a commercial raw food diet
O’Halloran, C. et al. (2020) Feline tuberculosis caused by Mycobacterium bovis infection of domestic UK cats associated with feeding a commercial raw food diet. Transboundary and Emerging Diseases.
The aim of this study is to report the clinical and epidemiological findings from a cluster of confirmed or highly likely Mycobacterium bovis tuberculosis cases in pet cats where there was circumstantial evidence of an association between the commercial raw diet fed to these cats and their M. bovis infection.
Cases where feline M. bovis infection was either strongly suspected by clinical presentation and owner-reported history or diagnosed by tissue culture or PCR, and where the cats had consumed the same raw commercial pet food as part or all of their diet, were included in the study.
Forty-seven cats were diagnosed with active tuberculosis disease, of which 36 were of pedigree breeds. The clinical signs noted most frequently were non‐specific signs of ill health, including combinations of lethargy (18/47) and hyporexia, and poor or declining body weight/condition (15/47). The clinical abnormalities reported most frequently were respiratory signs (34/47) and abdominal masses (23/47). Antemortem diagnostic imaging of the alimentary tract and associated structures revealed gross pathology in 31/47 cases.
Diseased tissue samples from eleven cats were obtained post-mortem and submitted for mycobacterial culture. Of these, five resulted in positive results for M. bovis genotype 10:a. PCR was carried out on samples from 15 cats, 12 of which were positive for the presence of mycobacterial DNA. Further analysis revealed one infection with an MTBC organism, and 11 were identified as M. bovis infections. 44/47 cases were identified as interferon‐gamma release assay positive.
The only common factors linking the cases was a specific brand of commercial raw cat food and the fact that they were mostly indoor cats. The raw cat food product was recalled in December 2018 due to failure of statutory meat inspection of the component venison. As far as possible, other sources of infection were explored and excluded, including wildlife contact, access to raw milk and living with people with active M. bovis infection.
Four owners and one veterinary surgeon were found to have high likelihood of latent tuberculosis infection. It was not possible to conclusively demonstrate a zoonotic transmission.
Limitations of the study are the incomplete histories for some of the cats and the lack of a positive M bovis 10:a culture for the pet food obtained directly from the owners.
This comprehensive write-up of the investigation into an outbreak of feline tuberculosis in pet cats highlights one of the potential risks of feeding raw food, the variety of presentations of Mycobacterium bovis tuberculosis and the investigations that can be undertaken in suspected cases in companion animals. It also highlights the importance of veterinary meat inspection for food safety for both humans and animals, as well as serving a timely reminder of the potential zoonotic risks presented by some patients.
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