Tuberculosis due to Mycobacterium bovis in pet cats associated with feeding a commercial raw food diet

Objectives: Mycobacterium bovis, a member of the Mycobacterium tuberculosis-complex, can infect cats and has proven zoonotic risks for owners. Infected cats typically present with a history of outdoor lifestyle and hunting behaviour, and cutaneous granulomas are most commonly observed.
Six young cats, living exclusively indoors in five different households across England were presented to separate veterinarians across the UK with various clinical signs due to tuberculous disease.
Methods: Investigations into the pyogranulomatous lesions, lymphadenopathy and/or pulmonary disease of these cases consistently identified infection with Mycobacterium bovis. Infection was confirmed by PCR where possible or was indicated with a positive interferon gamma release assay (IGRA) where material for PCR was unavailable. In-contact, cohabiting cats were screened by IGRA and follow-up testing undertaken/advised where these were positive. A lifestyle investigation was undertaken to identify the source of infection.
Results: Six clinically sick cats and seven in-contacts have been identified with evidence of M. bovis infection. Five clinical cases were either too sick to treat or deteriorated despite therapy, giving a mortality rate of 83%. Lifestyle investigations revealed the common factors between clusters to be; that affected cats had mycobacterial infections speciated to M. bovis, were exclusively indoor cats and were fed a commercially available raw food product produced by a single manufacturer. The Food Standards Agency, Animal and Plant Health Agency, Public Health England and the food manufacturer concerned have been notified/informed.
Other possible sources of exposure for these cats to M. bovis were explored and were excluded; including wildlife contact, access to raw milk, the presence of rodent populations inside the buildings in which the cats lived, and exposure to known infectious humans.
Conclusions and relevance: Upon investigations, our results provide compelling, if circumstantial, evidence of an association between the commercial raw diet of these cats and their M. bovis infections.