Experimental infection of domestic swine with Baylisascaris procyonis from raccoons.

Six 8-week-old ascarid-naive pigs which were experimentally infected with 72,000 embryonated Baylisascaris procyonis eggs of raccoon origin developed lesions limited to the intestines and liver. Intestinal lesions consisted of multifocal areas of inflammation by macrophages, eosinophils, and lymphocytes in the mucosa and submucosa, in association with Baylisascaris larvae; similar lesions were seen in the mesenteric lymph nodes. Typical white, granulation type, multifocal interstitial hepatitis ("milk-spots"), 1 to 5 mm in diameter, were seen in the livers by 7 days, with resolution by 47 days. Microscopically, these consisted of multifocal areas of marked periportal and interlobular edema, and influx of eosinophils, and large intralobular aggregates of eosinophils. At 47 days, hundreds to thousands of small white granulomas were seen on the serosa of the intestines; microscopically, they were discrete collections of macrophages, lymphocytes, and eosinophils in the submucosa and muscle layers surrounding nonviable remnants of Baylisascaris larvae. Larvae or lesions were not seen in other tissues, including the brain. These experiments indicated that B procyonis will undergo limited migration in swine and can produce typical white spots in the liver. The larvae were killed by cellular reactions in the intestinal wall and liver, and, unlike the situation in most other animals infected with this parasite, no somatic migration or CNS disease occurred after infection.