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

SALMONELLOSIS 243important to identify and eliminate individual carriers. Infection by S. dublin can bediagnosed serologically in a herd, but not in individual cattle. As a screening test,the S. pullorum antigen can also be used in detecting antibodies for the lipopolysaccharideof S. enteritidis in chickens. Seroagglutination with the S. abortus equi antigencan be used as a preliminary test prior to culture in mares that have aborted.Postmortem examinations of animals primarily use cultures from the mesentericlymph nodes.Surveillance of food processing requires that cultures be made from product samplesat different stages of preparation, and from utensils and surfaces that come intocontact with the food. Special sampling methods have been developed for differentkinds of foods.Control: Given current conditions under which cattle and poultry are raised,transported, marketed, and slaughtered, as well as existing food processing practices,it is impossible to obtain salmonellae-free foods of animal origin. Control iscurrently based on protecting man from infection and reducing its prevalence in animals.Veterinary meat and poultry inspection and supervision of milk pasteurizationand egg production are important for consumer protection.Another important control measure is the education of food handlers, both incommercial establishments and in the home, about correct cooking and refrigerationpractices for foods of animal origin, and about personal and environmental hygiene.Epidemiological surveillance by health authorities is necessary to evaluate themagnitude of the problem in each country, locate the origins of outbreaks, and adoptmethods designed to reduce risks.In animals, salmonellosis control consists of: (a) elimination of carriers, whichis currently possible for pullorum disease and fowl typhoid by means of serologictests; (b) bacteriologic control of foods, mainly of such ingredients as fish,meat, and bone meal; (c) immunization; and (d) proper management of herds andpoultry farms.Immunization may be an important method for preventing animal salmonellosis.Two types of vaccines are being used: bacterins and live attenuated vaccines.Bacterins are administered parenterally, usually in two doses two to four weeksapart. Commercially available bacterins act against S. dublin, S. typhimurium, andS. abortus equi. Live salmonellae vaccines are administered orally; they are usuallygenetically defective mutants. In the US, strains of S. dublin and S. typhimurium thatare unable to synthesize aromatic amino acids are used. Vaccines that are unable tosynthesize purines are used against these serotypes and S. choleraesuis in Germany.These vaccines are avirulent and do not revert to the virulent state.In the US, a vaccine has been developed against S. choleraesuis, with a strainattenuated through repeated selection of a virulent strain with passes of neutrophilsfrom salmonellosis-free swine. In this way, the vaccine strain lost the 50-kilobaseplasmid, which is a virulence factor (Kramer et al., 1992). Live vaccines stimulatea greater cell-mediated immune response than bacterins, which primarily promote ahumoral response with little or no association with protection. Oral administration(whether of bacterins or live vaccines) has the advantage of producing local immunityin the intestine and reducing elimination of salmonellae in feces. Parenteraladministration of live vaccines can sometimes cause adverse reactions due to endotoxins(WHO Expert Committee on Salmonellosis Control, 1988).