Mycobacterial infections are recognised with increasing frequency in cats in the UK. Over 1 per cent of all routine histopathological submissions from UK cats are found to have changes consistent with mycobacteriosis, which is thought to be an underestimate of the true prevalence. Mycobacteriosis can be highly variable in clinical presentation, challenging to definitively diagnose, and difficult to manage to obtain satisfactory clinical outcomes. Additionally, there is potential for zoonotic transmission of infection. Recent research efforts have improved our understanding of the aetiology, pathophysiology and therefore treatment options for these diseases. This article outlines an updated approach to diagnosing and managing clinical cases of feline mycobacteriosis in the UK.

Mycobacterium bovis can cause tuberculosis (TB) in social mammals including lions, cattle and man, but canine infections are considered rare. In 2016/17 we investigated a M. bovis TB outbreak in a pack of approximately 180 Foxhounds within the bovine TB Edge Area of England. We employed a combination of immunological tests including an interferon gamma release assay (IGRA) and a serological assay (DPP VetTB, Chembio). Test‐positive hounds were euthanased and subjected to post‐mortem examination (PME). Overall 164 hounds were tested; 97 (59%) responded positively to at least one test. Eighty‐five (52%) dogs responded to M. bovis antigens by IGRA while only 21 (12.9%) had detectable serological responses. At PME three hounds (3.1%) had visible lesions (VL) due to M. bovis infection, later confirmed by culture. Samples from 24 non‐VL hounds were cultured and M. bovis infection was confirmed in a further three hounds (11%). This study is the first investigation and report of an outbreak of M. bovis TB in a canine species. We establish that, in principle, diagnostic tests used for identifying infected individuals of other species can effectively be used in the dog. Further work is urgently needed to establish the sensitivity and specificity of the testing approach used in this study for future clinical application.

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. The aim of this study is to describe an outbreak of tuberculous disease commencing with six young cats, living exclusively indoors in five different households across England, being presented to separate veterinarians across the UK with a variety of clinical signs. Methods Investigations into the pyogranulomatous lesions, lymphadenopathy and/or pulmonary disease of these cases consistently identified infection with M 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. Incontact, cohabiting cats were screened by IGRA and follow-up testing was undertaken/advised where results were positive. A lifestyle investigation was undertaken to identify the source of infection. Results Six clinically sick cats and seven in-contact cats were 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 & 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.

Case series summaryThis paper describes the clinical presentation, diagnostic imaging findings and outcome in four cats with confirmed joint-associated tuberculosis. The cats were 2–6 years of age, and immune competent. Three cases had tuberculosis affecting only one joint, whereas one case had at least three joints affected. Two cases were caused by Mycobacterium bovis, and the other two were caused by Mycobacterium microti. Radiological findings included osteolysis, periosteal reaction and associated soft tissue swelling. Two cases were euthanased and two cases responded well to amputation and follow-on antibiotic therapy.Relevance and novel informationTo our knowledge, this is the first publication of a series of cats with joint-associated tuberculosis. Although tuberculosis is not common, a high degree of suspicion is needed to avoid delayed diagnosis. This case series highlights the importance of considering mycobacterial disease as a differential for joint disease in cats.

Mycobacterial diseases are being more frequently diagnosed in companion animals in first opinion practice in the UK. These infections can be challenging both to diagnose and manage; this and a previous article aim to give an overview of the relevant background and epidemiology, management and prognosis for companion animal mycobacteriosis (CAM). This second article explores the treatment options available to clinicians, as well as some of the considerations required before treatment is started.

This study describes clinical and histopathological features, treatment, and outcome of cats diagnosed with ocular mycobacteriosis. Cases diagnosed from 2012 to 2017 were reviewed for (a) histopathological evidence of ocular (pyo)granulomatous inflammation containing acid-fast bacilli with mycobacterial morphology, (b) positive mycobacterial culture and/or mycobacterial DNA identified by polymerase chain reaction of ocular tissue, or (c) presumed mycobacteriosis based on ophthalmic examination and positive interferon-gamma release assay. Twenty-five cats (31 eyes) were included; 14 cats (17/31 eyes, 55%) were blind at presentation (unilateral: n = 12 cats; bilateral: n = 2 cats); one unilaterally affected cat later became bilaterally blind. Another 5 cats (7/31 eyes, 23%) became blind after initially being bilaterally visual (unilateral: n = 3 cats; bilateral: n = 2 cats). The commonest ocular finding was uveitis (87%). The main histopathological features were granulomatous to pyogranulomatous chorioretinitis with retinal detachment, anterior uveitis, optic neuritis, episcleritis, scleritis, and/or retrobulbar cellulitis. Nineteen cats (76%) had systemic signs, with disseminated disease being diagnosed in 9, defined by interstitial pulmonary disease, generalized lymphadenopathy, and/or nonocular infection. Nine cats were diagnosed with Mycobacterium bovis, 2 with Mycobacterium microti, 1 with Mycobacterium tuberculosis complex, and 1 with Mycobacterium avium-intracellulare complex. The infecting species was unknown in the remaining cats. Combined surgery (enucleation: n = 5 cats; biopsy: n = 3 cats) and systemic treatment with 2 or 3 appropriate antibiotics for 2 to 7 months resulted in remission in 8 of the 10 cats treated; however, the cat treated with dual therapy relapsed after 8 months. A total of 16 cats (64%) were euthanized; 2 were lost to follow-up.

Mycobacterial diseases are being more frequently diagnosed in companion animals in first opinion practice in the UK. These infections can be challenging both to diagnose and manage; this and a following article aim to give an overview of the relevant background and epidemiology, diagnosis, management and prognosis for companion animal mycobacteriosis (CAM). This first article discusses the different mycobacterial species involved with CAM, the epidemiology and the various clinical presentations which may result from infection.

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