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Panniculitis, due to Mycobacterium smegmatis, in two Finnish cats

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Pyogranulomatous panniculitis due to infection by Mycobacterium smegmatis was diagnosed in two cats in Finland, a country with a rather cold climate. The diagnosis was confirmed by sequencing of the 16S rRNA gene, which gave a perfect match with the M smegmatis strain ATCC 19420. Gene sequencing makes it possible to distinguish M smegmatis from closely related mycobacteria such as M goodii sp.nov. Diagnosing this entity seems to be a question of having a high index of suspicion. The appearance of the disease as well as sampling is described in detail. In our first case an initial erroneous diagnosis of Nocardia species considerably delayed our arriving at the right diagnosis. The first patient has now been followed for more than 7 years. Her disease is chronic, but she is not systemically affected. Several antimicrobials were tried. Probable side effects of enrofloxacin medication are described.

Mycobacterium smegmatis is an opportunistic bacterium, which is considered to be widely distributed in nature (Kamala et al 1994, Tsukamura 1976). It is capable of causing a rare, but well documented pyogranulomatous dermatopanniculitis in cats (Wilkinson et al 1982, Wilkinson & Mason 1991,Malik et al 1994, 2000). This disease has proven difficult to treat. The inguinal fat pad is one predilection site for the infection caused by M smegmatis. Wilkinson, in Australia, first described this condition in cats in 1982. Most reports of this entity come from Australia, where it seems to be a well recognised problem, the largest material being the microbiological characterisation by Malik et al (2000) of no less than 40 strains of M smegmatis isolated from cases of clinical panniculitis in cats. From outside Australia there are only a couple of cases of M smegmatis in cats (Kunkle et al 1983, von Weber et al 2000). Initially it seemed that M smegmatis had clinical relevance only in warm and humid areas, but newer reports seem to contradict this (Malik et al 2000). This report of two Finnish cats further confirms that M smegmatis should also be suspected in colder climates.

M smegmatis is considered to be an organism of low virulence. The first reported human infection was a pleuropneumonia complicating exogenous lipoid pneumonia reported by Vonmoos (1986). Since then at least 26 human cases have been reported, many of which are wound infections in warm climates (Wallace et al 1988, Newton et al 1993, Newton & Weiss 1994). In the records of The National Public Health Institute of Finland there are no reports of M smegmatis causing clinical human disease in Finland in the past 20 years (Kokki, personal communication). And according to the documentation available at the National Veterinary and Food Research Institute of Finland it has, at least during the last 12 years, not been identified in clinical samples of domestic animals in Finland (Seppänen, personal communication).

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