Mycobacteriosis in small animals

To date, mycobacteriosis in small animals has only been sporadically documented, primarily in the context of case reports or case series. Therefore, practitioners often do not include mycobacteriosis in their list of differential diagnoses. Medical records of small animals from the Pathology of the University of Veterinary Medicine Vienna, the Pathology Service of the Schwarzman Animal Medical Center in New York, and the Institute of Animal Pathology of the Freie Universität Berlin were searched retrospectively for cases of proven or suspected mycobacteriosis. Twenty-two cases, in which histopathological findings including Ziehl-Neelsen staining of biopsy or necropsy samples suggested mycobacteriosis, were included in the retrospective study. Data on medical history, clinical signs, further diagnostics, PCR, and sequence analysis, histopathology, treatment, and outcome were analyzed if available. PCRs and sequence analysis were successfully performed in 21 cases. One case was confirmed by culture only. Among the 22 cases, 14 were cats, four rabbits, three ferrets, with one case each involving a dog and a chinchilla. All detected mycobacteria belonged to the non-tuberculous mycobacteria (NTM), with M. avium (n = 14) being the most frequently detected. Most common signs observed during the clinical examination were gastrointestinal disorders (n = 12), abdominal masses (n = 5), peripheral lymphadomegaly (n = 4), respiratory signs (n = 4) and dehydration (n = 4). Several animals showed unspecific signs. Only one cat was treated with specific antimycobacterial therapy (triple antibiosis), but therapy was not successful because of the advanced stage of the disease. Only one patient gained remission, the others were either euthanized, deceased, or data was not available. The conclusion of this report is to highlight, that although it is a rare disease, mycobacteriosis should be considered as differential diagnosis not only in animals with cutaneous signs but also with gastrointestinal signs, respiratory signs or lymphadenomegaly and abdominal masses particularly when cytology or histopathology reveals a (pyo-)granulomatous inflammation. In suspicious cases, Ziehl-Neelsen staining to detect acid-fast bacteria should be initiated. If positive, confirmation of mycobacteria should be performed by PCR or culture. The results indicate that the prognosis for a mycobacterial infection should be considered guarded.