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. The organs most commonly infected include the terminal small intestine and the large intestine, lymph nodes, liver, and spleen. Immunodeficient rodents are more severely affected.