Abbey Veterinary Services

DIAGNOSTIC HISTOPATHOLOGY AND CYTOLOGY

CASE OF INTEREST

A Case of Feline Disseminated myocbacteriosis

By Richard Fox, Veterinary Pathologist

A nine-year-old male, neutered, domestic long haired cat developed firm intradermal masses, which became alopecic and ulcerated. Concurrent bilateral submandibular lymphadenomegally was also present. These lesions developed over a period of several weeks (figure 1).

Figure 1. A photograph of a typical lesion highlighting an area of cutaneous ulceration and alopecia (area of the calcanion tenon).(Supplied by Danielle Gunn-Moore, Feline Unit, Edinburgh University)

Radiography revealed diffuse miliary opacities through all lung fields and ultrasonography identified multifocal hyperechoic areas within the spleen. Surgical biopsy (excisional) of one of the submandibular lymph nodes and a cutaneous lesion was performed. Histological examination revealed effacement of the superficial to deep dermis and subcutis by large numbers of macrophages and neutrophils arranged in coalescing nodules, with small foci of coagulation necrosis. There was extensive ulceration (not shown).

Figure 2. Histological section of skin displaying multifocal to coalescent areas of dermal and subcutaneous pyogranulomatous inflammation (x2 obj.). HE Stain.

The granulomas were composed of an admixture of neutrophils and epithelioid macrophages, peripherally located plasma cells and fewer lymphocytes, all supported by proliferate fibrovascular stroma (figure 2 & 3).

Figure 3. High power image of macrophages and neutrophils separated by fibrovascular supporting stroma (x40 obj.) HE stain.

Ziehl-Neilson (ZN) staining revealed moderate numbers of acid-fast intrahistiocytic rod-shaped bacteria (approximately 3μm in length)(figure 4).

Figure 4. Image of intrahistiocytic acid-fast bacteria taken under oil immersion (x100 obj.) ZN.

After indicating probable Mycobacterial infection tissue is now being cultured by the Veterinary Laboratory Agengy in Weybridge. The presence of Mycobacterium bovis in pet mammals is now a notafiable disease in the UK (only when confirmed whilst culturing for bacteria or from a suspicion in a carcase at present!). Other species, however, are involved i.e. M. avium. avium or M. microti. Some other species of mycobacteria have been found to be zoonotic but often in patients which are already naturally or chemically immunosupressed. Mycobacterial syndromes seen in cats therefore include tuberculosis, feline leprosy and opportunistic mycobacteriosis.

Other potentially pathogenic mycobacteria include M. lepraemurium, which causes leprosy in rats, and a similar, or possibly the same, organism which may be one of the cause feline leprosy. Opportunistic mycobacteria are usually saprophytic, but a number of species have been reported to cause disease in cats. These include M. chelonae-abscessus, M. fortuitum / peregrinum group, M. smegmatis, M. phlei, M. genavense, M. simiae, M. thermoresistible, M, flavescens, M. xenopi and M. terrae complex.

In this case systemic infection was suspected due to the changes evident within the lung fields radiographically and the spleen ultrasonographically. The majority of cases however seem to present as a non-healing mass often with ulceration without systemic signs, presumably indicating these may be localised or relatively recent infections. If drug therapy is sought its application should be taken in context with culture results, owner compliance and the extent of the disease. For more information please read the Feline TB notes in the download section of our website or on the Feline Advisory Bureau's website here.

With regard to Bovine Tuberculosis the evidence would suggest that cats become infected by exposure to infectious material from tuberculous cattle or badgers (or other maintenance hosts of M. bovis). Cats are therefore considered spillover hosts of M. bovis and, indeed, removal of the source of infection in cattle or wildlife would be expected to result in a reduction in the incidence of bovine TB in cats. However, cats are not true end hosts, as the disease presentation makes them (at least theoretically) capable of infecting other cats and other mammals, including humans.

Bacteriological culture is the only available method to confirm a presumptive diagnosis of M. bovis infection. A PCR assay is available from the VLA for cases in which fresh tissue is not available but is not free and only able to confirm the presence of the Mycobacterial genus only. Therefore, veterinary practices and referral laboratories should submit the whole carcase to the nearest VLA regional laboratory. Fresh (unfixed) tissue samples or a swab should be sent directly to the TB Diagnosis Laboratory at VLA – Weybridge. Any material submitted should be accompanied by a full case history as well as the name, address and postcode of the owner.

Mr. Keith Jahans, Veterinary Laboratories Agency (DEFRA), Weybridge,UK .
Telephone number: 01932 357280

Acknowledgments:

Thanks to Danielle Gunn-Moore (for the gross image presented here) ,Feline Unit , Edinburgh University.

References:

1. GUNN-MOORE, D. A. & SHAW, S. (1997) Mycobacterial disease in the cat. In Practice 19, 493-501.
2. MONIES, R. J., CRANWELL, M. P., PALMER, N., INWALD, J., HEWINSON, R. G. & RULE, B. (2000) Bovine TB in domestic cats. Vet Rec 146, 407-408.
3. MONIES, R. J., de la RUA R., JAHANS K. (2006) Bovine tuberculosis in cats. Vet Rec. Apr 8;158(14):490-1.
4. Infectious Pyogranulomatous Inflammatory Disorders. In: Skin Diseases of the Dog and Cat, 2nd edition (2005), Gross, Ihrke, Walder and Affolter pp. 278-288.