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

ZOONOTIC TUBERCULOSIS 289Most cases of swine tuberculosis are due to the M. avium complex. Thus, the reductionof avian tuberculosis has also helped lower the rate of infection in swine. InGreat Britain, as tuberculosis of bovine origin declined, infections caused by MACincreased proportionally (Lesslie et al., 1968). The total number of confiscationsdue to generalized tuberculosis was reduced even more drastically. In some LatinAmerican countries, M. bovis is the cause of 80% to 90% of tuberculous lesions inswine. The relative proportions of M. bovis and MAC as the cause of swine tuberculosisare reversed when M. bovis infection is controlled in cattle, as it has been inseveral European countries and in the US.MAC usually causes adenitis of the digestive tract and, more rarely, a generalizeddisease (see the chapter, “Diseases Caused by Nontuberculous Mycobacteria”).Swine are also susceptible to the human bacillus (M. tuberculosis), which producesan infection of the lymph nodes that drain the digestive system and, morerarely, generalized tuberculosis. The main sources of infection are kitchen scrapsand leftovers from tuberculosis sanatoriums. This infection has been confirmed inseveral countries in the Americas, Europe, and Africa.Swine-to-swine transmission of the infection is insignificant. Intestinal lesions arehyperplastic, and ulcers that would cause the agent to be shed are not observed.However, swine may transmit the infection to other swine when they have pulmonary,uterine, or mammary lesions (Thoen, 1992).If there is generalization of the infection caused by MAC, the lesions appear indiffuse form and there is little tendency toward encapsulation. The cutaway view ofa lesion generally shows a smooth surface and there may be foci of caseation, butcalcification is minimal. Lesions caused by M. bovis or M. tuberculosis, in contrast,are caseous and well-circumscribed by fibrosis with pronounced calcification(Thoen, 1992). Other bacteria, for example Rodococcus equi, can produce lesionssimilar to tuberculous lesions.SHEEP AND GOATS: Tuberculosis in sheep is generally rare and sporadic. In the fewcases described, the most important agent was M. avium,followed by M. bovis. Onlytwo cases involved M. tuberculosis. In research in New Zealand stemming from aprogram to eradicate bovine tuberculosis, multiples cases of infection by M. boviswere confirmed among sheep sharing the same pasture with infected cattle. In onearea, 597 sheep were given the tuberculin test on the inner thigh and 108 (18%) reactorswere discovered. Lesions, mostly in the lymph nodes, were found in 43 (61%)out of 70 necropsies. The lungs were affected in eight sheep (Davidson et al., 1981).A similar result was observed in another region of New Zealand, on land where theprevalence of tuberculosis in cattle and opossums (Trichosurus vulpecula) was high.The tuberculin test yielded positive results in 11% of the sheep, and was judged tohave a sensitivity of 81.6% and a specificity of 99.6% (Cordes et al., 1981).Prevalence in goats seems to be low. In countries with advanced programs to eradicatebovine tuberculosis, the infection in goats is monitored, since this species issusceptible to M. bovis, frequently suffers from pulmonary tuberculosis, and canreinfect cattle. Nannies also suffer from tuberculous mastitis and their milk mayconstitute a danger to the consumer. In addition, goats are susceptible to M. aviumand M. tuberculosis, and the latter agent sometimes causes generalized processes.Little is known about the disease’s occurrence in goats in developing countries,since these animals are generally slaughtered without veterinary inspection.