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

ZOONOTIC TUBERCULOSIS 293In South Africa, tuberculosis has been diagnosed in many wild species: the Capebuffalo (Syncerus caffer), the greater kudu (Tragelaphus strepsiceros), and the forestduiker (Cephalophus grimmia), among others (Pastoret et al., 1988).Source of Infection and Mode of Transmission (Figure 20): The main reservoirof M. bovis is cattle, which can transmit the infection to many mammalian species,including man. Man contracts the infection primarily by ingesting the agent in rawmilk and milk products, and secondarily by inhaling it.Tuberculosis is transmitted among cattle mainly via aerosols. The digestive tractis an important route of transmission prior to weaning.A human infected by M. bovis who suffers from the pulmonary or urogenital formof tuberculosis can retransmit the infection to cattle. This phenomenon becomes particularlyevident during the final stages of bovine tuberculosis eradication.Tuberculosis in swine, goats, and sheep has as it principal source of infection cattle,fowl, and occasionally man. Swine are infected enterogenously, and retransmissionto other swine, other species, and man is thought to be rare. Goats can constitutea source of infection for man and for cattle.Dogs often contract the infection from humans and, less frequently, from cattle.They may in turn retransmit it to man and cattle. Dogs become infected via thedigestive and respiratory tracts. The principal source of infection for cats is cattleand, to a lesser degree, man. The route of entry is mainly oral. At times, cats can bea source of infection for cattle and humans.Among wild animals in captivity, monkeys are particularly interesting because oftheir susceptibility to M. tuberculosis and M. bovis. They contract the infection fromman by inhaling the agent. Tuberculous primates constitute a health risk for humans.Figure 20. Tuberculosis (Mycobacterium bovis). Mode of transmission.TuberculousbovineMainly airborne route;digestive route (suckling calves)BovineDigestive route, mainly throughraw milk and milk products;less frequently via airborne routeDigestive route, mainly through rawmilk and milk products;less frequently via airborne routeOccasionally reinfection of bovinesvia airborne routeSwine, sheep,goats, horses,dogs, cats,wild animalsMan