Mycobacterium microti infection in the cat: a case report, literature review and recent clinical experience

Abstract

Overview: Mycobacterium microti infection is infrequently described in cats in the veterinary literature. It can be one of a large number of possible differential diagnoses in a feline patient with dermal nodules and non-healing draining ulcers, and can occasionally spread to involve the lungs and/or other areas of the body.

Case summary: This report describes the clinical signs, eventual diagnosis and variable response to treatment in a cat in Switzerland with recurrent cutaneous M microti infection. Only after several diagnostic and therapeutic attempts, over more than 2 years, was the species of Mycobacterium finally identified and targeted therapy given.

Practical relevance: For any cat in which there is even a low suspicion of mycobacterial infection, the authors recommend that an aggressive diagnostic approach is taken. Tissue specimens should be collected and frozen early on, and, as soon as acid-fast bacilli are detected, samples should be sent to a mycobacterial reference laboratory for definitive identification.

Literature review: A review of the literature relating to the aetiopathogenesis, diagnosis and management of M microti infection in cats and dogs is included. This is supplemented with clinical and therapeutic experience gained from this case and other, unpublished cases managed over the past 15 years by one of the authors (DGM).

FIG 1

Mass on the left mandible (area is shaved), at the time of biopsy in July 2008

FIG 2

Deep dermal and subcutaneous granulomas. Haematoxylin & eosin stain, bar = 400 μm

FIG 3

Epithelioid macrophages admixed with scattered neutrophils, lymphocytes and plasma cells. Haematoxylin & eosin stain, bar = 100 μm

FIG 4

Rare acid-fast bacilli (AFB) within epithelioid macrophages. The bacteria (arrow) appear as slender rods of approximately 5 × 2 μm with a hooked end. Ziehl-Neelsen stain, bar = 5 μm

FIG 5

Spoligotyping patterns of amplified DNAs are shown. The numbers above each pattern represent the spacers. Water, M tuberculosis H37Rv and M bovis BCG were used as controls; 1 = DNA of the chin nodule

FIG 6

The cat, pictured in April 2009, when the antibiotics were stopped