Transmission of Salmonella in Humans and Animals and its Epidemiological Factors

Abstract

Over 2,500 Salmonella serovars cause typhoidal and non-typhoidal salmonellosis, which has economic and public health importance worldwide. The routes, modes, and vectors of Salmonella transmission in humans and animals, including the factors that affect them are important in the understanding of the epidemiology, prevention, and control of the disease. This study aims to identify the routes, modes, and vectors of transmission of Salmonella, including the factors that enhance the spread, maintenance, and persistence of the organism in humans and animals. This was achieved by using a Google search engine to obtain peer-reviewed articles on the keywords of this study. The major route of transmission of Salmonella in humans is faecal-oral, while the transovarial route has also been reported in poultry. Ingestion of contaminated food or water, contaminated materials from pets/wildlife, infected persons, and transmission to the young through the placenta are described as modes of transmission of Salmonella in humans. Salmonella Typhimurium (S.Typhimurium), Salmonella Enteritidis (S. Enteritidis) and Salmonella Senftenberg (S. Senftenberg) attach efficiently to vectors like fruits and vegetables with the aid of AgfD-regulated-adhesin, biofilms, and flagella. The organism can also invade plant tissues before transmission to humans and animals. Phytophagous hemipteran and cynanthropia/coprophagic insects serve as vectors of transmission by forcibly excreting ingested Salmonella and through their intermittent habitat and diet changes, respectively. Lice serve as vectors by ingesting viable strains of the organism, after they reach a maximum titre of 0.5–5.0 ×107 within 6–8 hours; Salmonella is thereafter shed and transmitted through their faeces. Factors that affect the transmission of Salmonella include pathogen, host and environment-related factors like increased antimicrobial resistance, intermittent shedding of the organism and rainfall, respectively. The knowledge of the routes, modes, vectors, and factors that affect the transmission of Salmonella will contribute to the body of knowledge on the epidemiology, prevention, and control of salmonellosis.