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

242 BACTERIOSESfecal matter can explain why direct contact is not always necessary, as in the case ofsome reptiles kept in or near a house (Morse and Duncan, 1974). Interhuman transmissionis particularly important in hospitals; children and the elderly are the principalvictims. In Baden-Würtenberg (Germany), an outbreak of S. enteritidis, phagetype 4, occurred in a home for elderly disabled persons. The same serotype andphage type was isolated from 95 residents and 14 employees. The source of infectionwas a dessert made of orange cream prepared with eggs with contaminatedshells (WHO Surveillance Programme for Control of Foodborne Infections andIntoxications in Europe, 1991).Institutional and nosocomial outbreaks are usually due to food that is undercookedand kept at the wrong temperature, or to a kitchen employee who is anasymptomatic carrier. Nosocomial cases require prompt epidemiological investigationbecause they can involve patients who, given their age or illness, can experiencesevere cases of salmonellosis (CDC, 1991).Insects, particularly flies, may have some role as mechanical vectors in very contaminatedenvironments.Carrier animals perpetuate the animal-to-animal cycle by means of their excretaor, in the case of fowl, infected eggs. Feed contaminated by such ingredients asbone, meat, or fish meal plays an important role as a vehicle of infection.Intensive cattle-raising in developed countries is a very important contributingfactor in the epidemiology of salmonellosis. Close contact between animals and theuse of concentrated feed or ingredients that may be contaminated create conditionsfavorable to outbreaks. In developing countries, the source of infection is mainly thecontaminated environment and water sources where animals crowd together.Animal-to-animal transmission occurs not only at the home establishment, butalso during shipping, at auctions and fairs, and even at slaughterhouses prior to sacrifice.Meat can become contaminated in abattoirs by means of contaminated equipmentand utensils during skinning and butchering. Contaminated water can be asource of infection for man and animals.The cycle of infection in fowl begins with contaminated eggshells or yolks.Contaminated eggs spread the infection in the incubator. When the eggs hatch, thenewborn chicks become infected and many of those that do not die become carriers.This is the most important mechanism at work when fowl in poultry yards becomeinfected. Another vehicle of infection may be contaminated feed. Cannibalism andthe ingestion of contaminated eggs also contribute to transmission of the infection.Non–species-specific serotypes spread easily from one animal species to anotherand also to humans.Role of Animals in the Epidemiology of the Disease: Since animals constitutethe reservoir of salmonellae (except S. typhi and the paratyphoid serotypes), theyplay an essential role in its epidemiology.Diagnosis: In humans, clinical diagnosis of gastroenteritis due to Salmonella isconfirmed by isolation of the etiologic agent from the patient’s stool, serologic typing,and, when necessary, phage typing and plasmid profiling. In the few cases ofsepticemia, the agent may be isolated from the blood during the first week of the disease,and from feces in the second and third weeks.Diagnosis of animal salmonellosis is also made by culturing fecal material. Forinfections caused by S. pullorum and S. gallinarum in fowl, serologic diagnosis is