MYCOBACTERIAL NODULAR GRANULOMAS AFFECTING THE SUBCUTIS AND SKIN OF DOGS (CANINE LEPROID GRANULOMA SYNDROME)

Objective To obtain a better understanding of a disease affecting dogs in which nodular mycobacterial granulomas are present in the subcutis or skin. Design Retrospective survey Procedure A diagnosis of an unid entified mycobacterial infection was made in 45 dogs following detecti on of acid-fast bacilli surrounded by granulomatous or pyogranulomatou s inflammation in tissue sections. Eight cases were identified from th e records of our diagnostic laboratory. In all cases culture for mycob acteria was unsuccessful. Another 37 cases were identified by practiti oners and veterinary pathologists in response to a survey mailed to ve terinary clinics throughout Australia. Data from these 45 cases were e ntered into a data base. The data set was incomplete, as some responde nts did not answer all questions. Results Over 90% of affected dogs ha d short coats and about half were Boxers or Boxer-cross dogs. A weak s easonal trend for the development of primary lesions in autumn and win ter was identified. Cases were recorded from New South Wales (35 dogs) , Western Australia (4), Queensland (4), Tasmania (1) and New Zealand (1). The subcutis and skin of the ears and head (including the ears) w ere involved in 64% and 85% of cases, respectively, for which lesion s ite was recorded. Culture was attempted but was unsuccessful in 19 cas es, including 11 cases where material was submitted to our laboratory and/or a Mycobacteria Reference Laboratory. Lymph node enlargement, in ternal organ involvement or constitutional signs were not a feature of the syndrome, and most lesions did not worry the dogs. Although many practitioners recorded a favourable response to therapy with doxycycli ne (response rate 57%) or amoxycillin-clavulanate (63%), spontaneous r esolution of infection was thought to have occurred in six of seven do gs (86%) not given systemic antimicrobials, and three dogs where antim icrobials had failed previously. A minority of cases failed to respond to antimicrobial therapy and continued to have chronic lesions. There was no discernible trend for dogs of a particular age or sex to be af fected. Conclusion This syndrome is caused by saprophytic mycobacteria of limited pathogenicity that give rise to lesions restricted princip ally but not exclusively to the subcutis and skin of body extremities. Fastidious growth requirements have prevented their isolation on synt hetic media used for culture of mycobacteria. Organisms presumably ent er the subcutis following a breach in integrity of the epidermal barri er and produce self-limiting disease in immunocompetent dogs. Lesions tend to resolve spontaneously. The possibility of a public health thre at from affected dogs is highly unlikely.