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

238 BACTERIOSESture to normal. Signs of abdominal pain are very pronounced. Abortion is common.The disease may be fatal within a few days or the animal may recover, in which caseit often becomes a carrier and new cases appear. Calves are more susceptible thanadults, and in them the infection gives rise to true epidemic outbreaks, often withhigh mortality. Septicemia and death are frequent in newborns. The carrier state isless frequent among young animals and occurs primarily in adult cattle. The infectionis almost always spread by the feces of a cow that is shedding the agent, but itmay also originate from milk.SWINE: Swine are host to numerous Salmonella serotypes and are the principalreservoir of S. choleraesuis. Serotypes that attack swine include S. enteritidis, S.typhimurium, and S. dublin. These serotypes are generally isolated from the intestineand from the mesenteric lymph nodes. S. choleraesuis is very invasive andcauses septicemia; it may be isolated from the blood or from any organ. Swine areparticularly susceptible and experience epidemic outbreaks between 2 and 4months of age, but the infection also appears in mature animals, almost always asisolated cases.Swine paratyphoid (S. choleraesuis) or necrotic enteritis occurs mostly in poorlymanaged herds living in poor hygienic conditions. It is frequently associated withclassic swine plague (cholera) or with such stress factors as weaning and vaccination.The most frequent symptoms are fever and diarrhea. The infection usually originatesfrom a carrier pig or contaminated food.Infection by other serotypes may sometimes give rise to serious outbreaks of salmonellosiswith high mortality.Because of the frequency with which swine are infected with different types ofsalmonellae, pork products have often been a source of human infection.SHEEP AND GOATS: Cases of clinical salmonellosis in these species are infrequent.The most common serotype found in gastroenteritis cases is S. typhimurium, butmany other serotypes have also been isolated. Serotype S. abortus ovis,which causesabortions in the last two months of pregnancy and gastroenteritis in sheep and goats,seems to be restricted to Europe and the Middle East (Timoney et al., 1988).HORSES: The most important pathogen among horses is S. abortus equi, whichcauses abortions in mares and arthritis in colts. It is distributed worldwide. As inother types of salmonellosis, predisposing factors influence whether the infectionmanifests itself clinically. Pregnant mares are especially susceptible, particularly ifother debilitating conditions are present. Abortion occurs in the last months of pregnancy,and the fetus and placenta contain large numbers of bacteria. This serotype isadapted to horses and is rarely found in other animal species.Horses are also susceptible to other types of salmonellae, particularly S.typhimurium. Salmonella enteritis occurs in these animals, sometimes causing highmortality. Calves suffer from acute enteritis with diarrhea and fever; dehydrationmay be rapid. Nosocomial transmission has been seen in hospitalized horses. FromApril 1990 to January 1991, in an outbreak among hospitalized horses, 97.8% of theanimals contracted the infection due to S. typhimurium var. copenhagen with thesame plasmid profile. Other strains of S. typhimurium var. copenhagen with a differentplasmid profile and S. enteritidis began to appear in February 1991(Bauerfeind et al., 1992).