Animals and Food of Animal Origin as a Potential Source of Salmonellosis: A Review of the Epidemiology, Laboratory Diagnosis, Economic Impact and Public Health Significance

Salmonellosis is an infectious disease of humans and animals caused frequently by two species of Salmonella (Salmonella enterica, and Salmonella bongori). Although primarily an intestinal bacterium, Salmonellae are widespread in the environment and are commonly found in farm effluents, human sewage and in any material that is subjected to fecal contamination. Salmonella cause diarrheal and systemic infections in humans. The infection most commonly results due to the consumption of food originating from animals and the environment. Studies have attributed that the subclinical infection in farm animals may lead to the contamination of meat, eggs, and milk or cause secondary contamination of fruits and vegetables that have been fertilized or irrigated with water containing fecal wastes. Salmonellosis causes significant economic loss in the management of farm animals. This can be attributed to the cost associated with the diagnosis and to treat the disease, the cost of cleaning and disinfection, and the cost of control and prevention. Moreover, emerging antimicrobial resistance can increase morbidity, mortality, and costs associated with disease management. Salmonellosis has both the social and economic consequences that require strong scientific and public health efforts to improve the situation. Because of the financial constraints, serological tests are conducted on a statistically representative sample of the population where the results are not always indicative of active infection in the herd. Enzyme-linked immunosorbent assays are available for some serovars of Salmonella and may be used for serological diagnosis and surveillance, especially in poultry and pigs. Vaccination, herd immunity, and antigenic cross-reactivity may compromise the diagnostic value of serological tests. Many inactivated vaccines are used against salmonellosis and some live vaccines are available commercially. Owing to the low efficacy of inactivated vaccines, oil or aluminum hydroxide adjuvants are used to improve their immunogenic properties. There is no vaccine to prevent salmonellosis in adults, whereas, a vaccine against Salmonella typhi has been developed, which is in use especially in children, but is only 60% effective. Prevention strategies include maintenance of sanitary/hygienic conditions in food processing plants, avoidance of cross-contamination of food, proper refrigeration of food, the supply of Salmonella free feed to animals, a strict inspection of meat originating from animals, detection and exclusion of carriers from food handling, and personal hygiene. Awareness should be created among the public about the risks associated with the consumption of raw meat, unpasteurized milk, smoked fish, un-cleaned vegetables, and contaminated water. This review attempts to highlight the role of farm animals in the transmission of salmonellosis, its epidemiology, laboratory diagnosis, economic impact, and public health significance.