zoonoses and communicable diseases common to ... - PAHO/WHO

ZOONOTIC TUBERCULOSIS 283ZOONOTIC TUBERCULOSISICD-10 A16 respiratory tuberculosis, not confirmedbacteriologically or histologically; A18 tuberculosis of other organsEtiology: The etiologic agents of mammalian tuberculosis are Mycobacteriumtuberculosis, the main cause of human tuberculosis; M. bovis, the agent of bovinetuberculosis; and M. africanum,which causes human tuberculosis in tropical Africa.This last species has characteristics halfway between those of M. tuberculosis andM. bovis. M. microti,which causes tuberculosis in rodents, should be added to theseagents, although it is not of zoonotic interest (nontuberculous mycobacteria are presentedin the chapter, “Diseases Caused by Nontuberculous Mycobacteria”).The principal agent of zoonotic tuberculosis is M. bovis; the agent in man andother primates is M. tuberculosis, which is the type species of the genus.Tuberculous mycobacteria are alcohol- and acid-resistant, nonsporogenic, grampositivebacilli. These mycobacteria are resistant to many disinfectants, desiccation,and other adverse environmental factors because the cell wall has a high lipidcontent.Phage typing is being used in epidemiological research on M. tuberculosis, andthe API ZIM system divides the genus into seven biovars (Casal and Linares, 1985;Humble et al., 1977). The use of phage typing was not widespread and the methodpractically fell into disuse. It has been replaced by DNA hybridization.Analysis of DNA fragments obtained through the digestive action of one or morerestriction endonucleases is useful for identifying strains of both M. tuberculosis andM. bovis (Collins and De Lisle, 1985; Shoemaker et al., 1986).Many authors prefer to refer to a single species (M. tuberculosis) and human andbovine types.Geographic Distribution: The distribution of M. bovis and M. tuberculosis isworldwide. M. africanum is prevalent in Africa, but it has also been isolated inGermany and England. M. africanum strains phenotypically related to M. tuberculosisare nitrase positive and are found in western Africa; those that are similar to M.bovis are nitrase negative and are isolated more frequently in eastern Africa (Grangeand Yates, 1989).Occurrence in Man: The prevalence of human tuberculosis of animal origin hasdiminished greatly in countries where mandatory pasteurization of milk has beenimplemented and where successful campaigns to control and eradicate the bovineinfection have been carried out. The British Isles, where the incidence of humaninfection due to M. bovis is currently low and is limited to the elderly, were once themost affected area due to the consumption of raw milk. However, despite the greatreduction in rates of human infection by bovine strains in Great Britain, tuberculosisoriginated by these strains continues to occur. From 1977 to 1979 in southeastEngland, isolations from 5,021 tuberculosis patients revealed 63 patients (1.25%)infected with “classic bovine strains” (M. bovis), 53 of which were Europeans and10, immigrants. Of these cases, 27 (42.85%) had pulmonary tuberculosis and 36(57.14%) had extrapulmonary tuberculosis. There was a marked difference in thefrequency of renal tuberculosis caused by M. bovis (23.8%) and M. tuberculosis