Med. Weter. 69 (3), 139-144, 2013

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Kalinowski M., Grądzki Z., Jarosz Ł., Adaszek Ł.
Rhodococcosis as a zoonosis
Rhodococcosis is known largely as an infectious disease of young foals that causes losses in the horse breeding industry. Besides in animals, the infection can also be a significant diagnostic, clinical and therapeutic problem in human medicine. The aim of the paper is to present the zoonotic aspect of rhodococcosis, including basic data about pathogen, epidemiology, pathogenesis, clinical picture, pathology, diagnosis and therapy of the disease. R. equi was isolated for the first time in 1923 by Magnusson in Sweden from a dead foal with the signs of pyogranulomatous pneumonia. The first case of human R. equi infection has been described in 1967 in a 29-year-old man subjected to immunosuppressive therapy. Hundreds of new cases of human rhodococcosis have been described since that time all over the world. The majority of human cases of R. equi infections concern patients immunodeppressed during the course of different diseases or treated with immunosuppressive drugs. However, 10-15% of cases concern fully immunocompetent patients. The role of farm animals as a primary source of infection to people has not been proved, but the importance of a contaminated environment seems to be evident. Molecular studies of human R. equi strains revealed that only 21% of isolates contained the typical for foal strains VapA plasmid. This suggests that the pathogenesis of the disease in humans may be different from that described in animals. Immunological investigations supporting the role of cell-mediated immunity in R. equi infections explain why AIDS patients with confirmed CD4+ lymphocytes deficiency and decreasing ability of INF gamma synthesis are more susceptible to infection in comparison to immunocompetent people. The clinical course of rhodococcosis in humans is varied, but in 80% of cases the process is localized in the respiratory tract. The mortality rate in immunosuppressed patients ranges between 20-55%. Diagnosis of rhodococcosis in humans is based on the isolation and identification of the pathogen in antemortem collected biological material. Radiology and CT may also be helpful. Myc. tuberculosis and Nocardia spp. infections should be included as a differential diagnosis. Treatment of rhodococcosis in humans, similarly to animals, usually requires a several-week course of a combination of 2-3 antibiotics. In practice intravenous application of vancomycin, carbapenem or aminoglycosides combined with oral administration of azithromycin and/or rifampin is used. In apparently cured individuals relapses occur frequently in which pathological changes are localized in primarily involved or in other tissues and organs.
Key words: rhodococcosis, zoonosis, epidemiology, diagnostics, therapy