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Over the past few weeks we have observed a marked increase in the incidence of Mycobacterial infections in cats from samples submitted to the laboratory from vets across the country. We have detected these in cytology specimens by observing non-staining rods on routine staining, which subsequently stain with ZN. The clinical presentations included the presence of an abdominal mass/abdominal lymphadenopathy, coughing with thoracic lymphadenopathy, pleural effusion typical of pyothorax and cutaneous swellings on the face or limbs. Feline mycobacteriosis can also involve any structure of the eye and can occur with or without concurrent systemic disease.
PCR has been performed in some of these cases revealing M. bovis. One case was from an indoor cat on a raw food diet (we do not yet know the dietary history of the other cats). There have been reports of cats infected with M. bovisafter feeding commercially available venison based raw food diet. The first 5 cases are described in the publication by O’Hallaron, with more cases being identified subsequently: Tuberculosis due to Mycobacterium bovis in pet cats associated with feeding a commercial raw food diet. Journal of Vet Surgery and Medicine O’Hallaron et al 2019 https://journals.sagepub.com/doi/10.1177/1098612X19848455
Given the variable presentations, vets should consider this as a differential in cats with the above clinical histories and consider the health and safety of colleagues when taking samples from suspected cases.
It is also very important that samples being submitted to the laboratory are clearly labelled as possible mycobacterial infection, so we can take extra precautions when handling the samples. PCR can be performed on FNA slides but these must not be stained. Hence it is important that we know if there is a clinical suspicion of mycobacterial infection so we can keep one slide back for PCR. We are able to dispatch samples to the Mycobacterium Reference Laboratory in Leeds where PCR testing is performed.