Mycobacterial Disease in a Population of 339 Cats in Great Britain: II. Histopathology of 225 Cases, and Treatment and Outcome of 184 Cases

Abstract

This study investigated 339 cases of feline mycobacterial infection, with histopathology findings from 225 cases, and treatment and outcome information from 184 cases. Tissue samples from cats with cutaneous lesions or suspicious masses at exploratory laparotomy were submitted to the Veterinary Laboratories Agency for mycobacterial culture over a 4-year period to December 2008. The study reviewed the files for information about histopathology, treatment and outcome, and blindly reviewed histopathological changes (including staining for acid-fast bacteria [AFB]) in a sub-set of 45 cases. When a cat is suspected of having a mycobacterial infection, accurate identification of the species involved helps to determine possible treatment options and prognosis. The study confirmed that histopathology and the presence of AFB are useful tools in the recognition of mycobacterial infection. Unfortunately, they did little to help determine the species of mycobacteria involved. The study identified a group of cats that were negative for AFB at the primary laboratory, but from which mycobacteria could be cultured; commonly Mycobacterium bovis or Mycobacterium microti. The study also identified a group of cats which where culture negative, despite typical signs of mycobacterial infection and positive AFB staining. Many cases responded favourably to treatment (56% of the cases where information was available), and many cats gained complete remission (42%). However, relapses were common (64%) and often followed by pulmonary and/or systemic spread that may have resulted from treatment with short courses of single drugs. This study shows that the diagnosis and treatment of feline mycobacteriosis is complex and challenging.

Mycobacterial Infections

“…Multinucleated giant cells are rarely present in dogs or cats. 4,30 The inflammatory foci are surrounded by a layer of macrophages, neutrophils, lymphocytes, and plasma cells and an outer layer (or background) of granulation tissue. The center of the tubercle may be necrotic.…”

Detection and Molecular Characterization of Mycobacterium microti Isolates in Wild Boar from Northern Italy

“…Occasionally, it was also found in llamas, cats, pigs, cows, and dogs (3,(6)(7)(8)(9)(10)(11)(12)(13). Recently, the widespread host range of M. microti seemed to be increasing, with reports of an infected cat population in England (9,14,15) and with accounts of new hosts, such as squirrel monkeys (16), meerkats (17), and South American camelids (18). In humans, infection by M. microti is infrequent, and to date only 27 cases have been reported in immunosuppressed and/or immunocompetent patients (19)(20)(21)(22)(23).…”

Incidence of Mycobacterial Infections in Cats in Great Britain: Estimate from Feline Tissue Samples Submitted to Diagnostic Laboratories

“…Unfortunately, many aspects of mycobacteriosis in this species remain unknown. While recent studies from Great Britain (GB) have advanced our overall understanding of these infections (reviewed in Gunn‐Moore, 2010; Bennett et al., 2011; Gunn‐Moore et al., 2011a,b; Lalor et al., 2012; Rhodes et al., 2011; Rüfenacht et al., 2011; reviewed in Greene and Gunn‐Moore, 2012), their current prevalence remains unknown.…”

“…Confirmation is by specialist culture of fresh tissue (reviewed in Greene and Gunn‐Moore, 2012) or molecular testing. Unfortunately, many samples fail to culture, even when typical AFB have been seen, and those that do can take up to 3 months to grow (Smith et al., 2009; Gunn‐Moore et al., 2011a,b).…”