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

290 BACTERIOSESHORSES: Tuberculosis is infrequent in horses. In countries where the incidence ofbovine infection is high, the principal agent of the disease in horses is M. bovis. Theinfection’s predominant route of entry is the digestive system. Lesions are generallyconfined to the lymph nodes of the digestive tract, where they produce a tissue reactionthat resembles tumors. Some cases of generalized infection, caused by both M.bovis and M. avium, have been described. Often, no lesions are found in infectionsproduced by M. avium. In Germany, the avian bacillus was isolated from 30% of 208horses with no apparent lesions.M. tuberculosis is seldom isolated from horses. In a study carried out sometime ago, only 13 of 241 typed strains corresponded to the human bacillus(Francis, 1958).The disease is very rare in asses and mules.It is interesting to note that horses are hypersensitive to tuberculin, and thus theallergenic test does not give reliable results.DOGS AND CATS: Dogs are resistant to experimental tuberculosis infection.Recorded cases in dogs are probably due to massive and repeated exposure broughtabout by living with humans with tuberculosis or frequently eating contaminatedfood. Infection may be produced by aerosols, or by ingestion of sputa, milk, and viscera.Almost 75% of the cases are due to the human bacillus and the rest to thebovine. The clinical picture is not characteristic. The only symptoms found in eighttuberculous dogs in New York City were anorexia, weight loss, lethargy, vomiting,and leukocytosis. Radiology revealed pleural and pericardial effusion, ascites, andhepatomegaly. Granulomatous lesions in soft tissues were similar to those observedin neoplasias (Liu et al., 1980). Infection mainly localizes in the lungs or mesentericlymph nodes; intestinal ulcers and renal lesions are sometimes found as well.Consequently, dogs can shed bacilli by coughing and in their saliva, feces, and urine.It has also been demonstrated that the etiologic agent can be present in the pharynxand feces of dogs living in the same house with tuberculous patients, even when theanimals show no tuberculous lesions. Although few cases of transmission from dogto man have been confirmed, a tuberculous dog (or even an apparently healthy animalliving with a tuberculous patient) represents a potential risk and should bedestroyed. A dog infected with M. bovis can, in turn, be a potential source of reinfectionfor cattle.Cats also have a great natural resistance to tuberculosis. M. bovis is the most commonpathogen in cats, and has been isolated in 90% of the cases. The agent gainsentry via the digestive tract when milk or viscera containing tuberculosis bacilli isconsumed. Cat-to-cat transmission of M. bovis in a scientific institution in Australiahas been described (Isaac et al., 1983). In countries where bovine tuberculosis hasbeen brought under control, infection in cats is rare, and the few recorded cases havebeen caused by M. tuberculosis and occasionally MAC.Destructive lesions are sometimes found; pneumonitis and cutaneous tuberculosisare frequent. In urban areas of Buenos Aires, a cooperative study was conducted bythe Pasteur Institute and the Pan American Institute for Food Protection andZoonoses (INPPAZ). M. bovis was isolated from the lesions of 10 of approximately150 cats studied (I.N. de Kantor. Personal communication). In New Zealandbetween 1974 and 1986, M. bovis was isolated from 57 cats. With the exception ofsix animals, all came from suburban and rural areas where tuberculosis is also pres-