Description
An update on mycobacteria in cats by Danielle Gunn-Moore. This talk will discuss the increasing recognition of these important potentially zoonotic and nosocomial infections in pet cats (and dogs) in the UK. We now know that ~1% of all feline tissue biopsies sent for routine pathology in laboratories in the UK are found to have histopathology changes consistent with mycobacterial infections. Of these cases, ~35% are found to have tuberculosis, with ~20% caused by Mycobacterium microti and ~15% caused by Mycobacterium bovis. Which infection is present is highly regionally-dependent with M. microti found in cats from Scotland, the North of England and the South-East of England, while cats with M. bovis infections come from the areas of UK where infected cattle and badgers are found, i.e. the South-West and West of England and Wales. The talk will cover how the cats are most commonly infected, which is particularly related to hunting small rodents, and what these infections can look like in the cat – which might not be as you expect. Most cases are cutaneous in nature and/or affect regional lymph nodes, especially the submandibular or popliteal lymph nodes. Only late on in infection does haematogenous spread to lungs eventually cause respiratory signs, typically dyspnoea. The talk will touch on tuberculosis in dogs, which while much less common than in cats, tends to present most commonly with fully disseminated disease. Making a diagnosis can be complex and frustrating. There is no gold-standard test; while Ziehl-Neelsen staining can suggest that mycobacteria are present, currently available advanced diagnostics (e.g. specialist culture, PCR tests and the IFN gamma release assay [IGRA]) can only identify ~50% of these infections. In addition, specialist culture results are typically not available for two to three months, sometimes longer; current PCR diagnostics are expensive and not reliable when only a few mycobacteria are present; and the IGRA blood test is costly and can be tricky to interpret in some cases. The results from a number of tests may need to be pieced together before you are certain of what you are dealing with. The discussion will review management options. While treating a cat of tuberculosis is always contentious – this statement belies a complex situation since many cats have only a single cutaneous lesion, and a confirmation of TB may take many months to be made. We need to look at each case in its entirety, considering the nature of the infection (once it is known) – since M. bovis is Notifiable in the UK; both infections are potentially zoonotic, but only M. bovis has been shown to spread from cats to their owners, notably when a cat has a cutaneous lesion that is draining pus containing large numbers of mycobacteria; both infections can potentially cause nosocomial infections within a veterinary practice, but only M. bovis has been shown to do this so far, again when a cat has a cutaneous lesion that is draining pus containing large numbers of mycobacteria; the extent and severity of the cat’s clinical signs (especially the presence of cutaneous lesions that are draining pus containing large numbers of mycobacteria); the household within which the cat lives and whether or not there are any immunosuppressed individuals; the complexity, expense and potential toxicity of potential treatment; the need for prolonged treatment which requires cat and owner compliance; and the need to use drugs that are used to treat tuberculosis in humans, amongst other things. Where appropriate cases (e.g. cases with non-ulcerated cutaneous lesions) are treated with two-to-three suitable drugs for up to six months the prognosis for an apparent cure or long-term remission can be as high as perhaps 70%; however, these are always complex and contentious cases to treat and the prognosis should be stated as guarded. Cases of canine TB are most typically severe and caused by M. bovis, so are euthanased.
Companion Animal Mycobacterial infections are being recognised with increasing frequency, especially in cats in Great Britain, where 1% of all feline biopsies submitted for routine histopathological analysis show changes consistent with mycobacteriosis; when these are cultured 19% are found to be caused by M. microti (the major cause of tuberculosis [TB] in rodents) and a further 15% by M. bovis (the major cause of TB in cattle, but also able to cause disease in humans and many other species). This talk will discuss how common mycobacterial infections are in cats (and dogs), their potential zoonotic risks, how they typically present, the complexities of diagnosis and the possible treatment options.