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

48 BACTERIOSESSeveral researchers have observed that young goats can be born with the infectionor become infected shortly after birth. Most of them recover spontaneously beforereaching reproductive age, but in some the infection may persist longer.The primitive conditions under which goats are raised constitute one of the mostimportant factors in the maintenance and spread of the infection in Latin America(Argentina, Mexico, and Peru) and in the rest of the developing world. In goat-raisingareas, it is common to find community-shared pastures, a lack of hygiene in makeshiftcorrals, nomadic flocks, and owners with little understanding of herd management.SHEEP: Two disease entities are distinguishable in sheep: classic brucellosis andram epididymitis. Classic brucellosis is caused by B. melitensis and constitutes apublic health problem equally or even more important than goat brucellosis in areaswhere the agent is found outside the American continent. In Latin America, theinfection in sheep has been confirmed only in some mixed goat and sheep flocksraised far away from intensive sheep-raising areas.While sheep brucellosis is similar in its symptomatology to the disease in goats,sheep appear to be more resistant to infection and, in mixed flocks, fewer sheep thangoats are found to be infected. Susceptibility varies from breed to breed. Maltesesheep are very resistant, while Middle Eastern Awassi (fat tail) sheep are very susceptible(Alton, 1985). Abortions are also less common. The infection tends to disappearspontaneously, and the high prevalence of the disease in some areas can bestbe attributed to poor herd management.Occasionally, sheep have been found to be infected by B. suis (biovar 2 inGermany) and B. abortus (in various parts of the world). These agents are not verypathogenic for sheep; they are acquired through contact with infected animals ofother species, and are usually not transmitted from sheep to sheep. However, transmissioncan occur, as in the case described in an outbreak occurring on a ranch inthe US (Luchsinger and Anderson, 1979).Ram epididymitis is caused by B. ovis. The clinical signs consist of genital lesionsin rams, associated with varying degrees of sterility. Sometimes the infection inpregnant ewes can cause abortion or neonatal mortality. Epididymitis is generallyunilateral but can be bilateral and the tail of the organ is most commonly affected.Adhesions may occur in the tunica vaginalis testis, and the testicle may be atrophiedwith varying degrees of fibrosis. Lesions cannot be seen or palpated in manyinfected rams, even though B. ovis may be isolated from their semen. Some of theseanimals develop lesions in more advanced stages of the disease. Early in the infection,the semen contains many brucellae, but with time the number decreases, andeventually the semen may be free of the infectious agent. When localized in the kidneys,B. ovis is also shed through the urine.HORSES: B. abortus and B. suis have been isolated from this species. The diseaseusually manifests itself in the form of fistulous bursitis, “poll evil” and “fistulouswithers.” Abortions are rare but they do occur (Robertson et al., 1973). B. abortushas been isolated from horse feces, but this is uncommon. Horses acquire the infectionfrom cattle or swine, but transmission from horses to cattle has also beenproven. Man can contract the infection from horses that have open lesions. In general,horses are more resistant to the infection. Cases of horse-to-horse transmissionare unknown. In areas where there is a high rate of infection, it is common to findhorses with high agglutination titers.