Mycobacterium avium subsp hominissuis infection in 2 pet dogs, Germany
It is not a rare finding that members of the Mycobacterium avium-intracellulare complex (MAIC) are detected as disease causing agents in humans, especially in association with lymphadenitis in children, pulmonary tuberculosis-like disease and disseminated infections, the latter occurring predominantly in immuno-compromised persons (e. g. AIDS patients). Similarly, important animal diseases are caused by agents of this group, e.g., avian tuberculosis and paratuberculosis in ruminants. Normally, infections seem to originate from environmental sources (soil, peat, water, dust, and feed). From the majority of mammals the M. avium species "hominissuis" is isolated, whereas in birds mostly the subspecies "avium" is detected. The subspecies differ by the content of insertion elements. These differences are used for molecular differentiation. Dogs are reported to be relatively resistent to M. avium infections. Neverthelss, we were able to detect two cases of infections caused by M. avium ssp. hominissuis in a one year old and a three year old dog, a miniature Schnauzer and a Yorkshire terrier, suffering from serious several weeks lasting clinical symptoms (therapy-resistant fever, lethargy, progressive weight loss, generalized lymphadenomegaly and diarrhea) leading finally to the necessity to euthanize the animals. Necropsy findings were corresponded to lesion expected in generalized mycobacterial infections: Enlargement of lymph nodes containing whitish granulomatous foci, granulomatous foci also in other organs (spleen, liver, thoracic region), intra-abdominal adhesions. Histological examination revealed (pyo)-granulomatous inflammation of lymph nodes, tonsils, liver, spleen, greater omentum, gut, kidney, lung and pleura. The granulomatous lesions exhibited central necroses surrounded by phagocytes and few neutrophils. Large numbers of acid-fast bacilli were detected microscopically. After processing of tissue and cultivation for two weeks bacteria were isolated and identified as Mycobacterium avium ssp. hominissuis. The zoonotic risk for humans originating from pet animals infected with M. avium ssp. hominissuis, should not be underestimated, especially since the diseases are normally characterized by chronic subclinical courses.