SHIGELLA INFECTION AS OBSERVED IN THE EXPERIMENTALLY INOCULATED DOMESTIC PIG, SUS SCROFA DOMESTICA

The domestic pig, Sus scrofa domestica, was investigated as a potentia l animal model for shigellosis. We examined the effects of pig age, pi g breed and antibiotic pretreatment upon Shigella infection. Shigella dysenteriae, and Shigella flexneri (both virulent and avirulent strain s) were utilized. Our results indicated that young (4-week-old), conve ntionally reared, domestic pigs were routinely, but briefly, colonized (average=3.5 +/- 2.5 days) following oral or gavage administration of S. flexneri, as determined by direct rectal cultures. The duration of S. dysenteriae colonization was significantly shorter. Inoculation of younger (2 days) or older (9 weeks) pigs with S. flexneri had no sign ificant effect on infection duration. Similarly, infection of 4-week-o ld pigs with virulent and avirulent strains of S. flexneri had no effe ct upon the duration of infection, nor did the use of a swine-passaged S. flexneri isolate. Marked clinical, histopathological (gross and mi croscopic) and immunohistopathological signs of disease were absent in all infections. However, in instances where microscopic histopatholog ical 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 for Salmonella choleraesuis, anoth er member of the Enterobacteriaceae and a prevalent pig pathogen. Take n altogether, our results indicate that the domestic pig is unsuitable as a model for shigellosis. (C) 1998 Academic Press.