The primary importance of Salmonella spp. is as zoonotic agents and as pathogens in immunocompromised mice and rats. S. enteritidis serotype typhimurium is the most common serotype infecting laboratory rodents, although the prevalence of asymptomatic carriers is unknown but probably low. Transmission is via ingestion of contaminated feed ingredients and water and by contact with contaminated bedding and animal facility personnel. Reports of natural outbreaks of disease are rare in the literature, probably because most infections are asymptomatic in normal hosts. When clinical effects are observed, reproduction is most prominently affected, while other signs are nonspecific.
Diarrhea is an uncommon finding.
Inbred mouse strains have a wide range of susceptibility to S. enteritidis. Susceptibility is determined by three distinct genetic loci. Following ingestion, the mucosa and Peyer's patches in the distal ileum are initial sites of invasion. From those sites the organism reaches the mesenteric lymph nodes and gains access to the vascular system, to be distributed throughout the body. Lesion development depends upon the distribution of the pathogen.