Shigellainfection as observed in the experimentally inoculated domestic pig,Sus scrofa domestica

The domestic pig,Sus scrofa domestica, was investigated as a potential animal model for shigellosis. We examined the effects of pig age, pig breed and antibiotic pretreatment uponShigellainfection.Shigella dysenteriae, andShigella flexneri(both virulent and avirulent strains) were utilized. Our results indicated that young (4-week-old), conventionally re ared, domestic pigs were routinely, but briefly, colonized (average=3.5±2.5 days) following oral or gavage administration ofS. flexneri, as determined by direct rectal cultures. The duration ofS. dysenteriaecolonization was significantly shorter. Inoculation of younger (2 days) or older (9 weeks) pigs withS. flexnerihad no significant effect on infection duration. Similarly, infection of 4-week-old pigs with virulent and avirulent strains ofS. flexnerihad no effect upon the duration of infection, nor did the use of a swine-passagedS. flexneriisolate. Marked clinical, histopathological (gross and microscopic) and immunohistopathological signs of disease were absent in all infections. However, in instances where microscopic histopathological evidence was used to correctly identify infected pigs, tonsillar lesions were the consistently noted criteria. The tonsils are believed to be an important portal of entry forSalmonella choleraesuis, another member of the Enterobacteriaceae and a prevalent pig pathogen. Taken altogether, our results indicate that the domestic pig is unsuitable as a model for shigellosis.