Experimental infection of newly weaned pigs with human and porcine strains of Serpulina pilosicoli.

Cultures of Serpulina pilosicoli 95/1000, isolated from a pig with porcine intestinal spirochetosis (PIS), and S. pilosicoli WesB, isolated from an Aboriginal child with diarrhea, were used to infect 5-week-old newly weaned pigs. Four of 12 pigs infected with strain 95/1000 and 2 of 12 pigs infected with strain WesB became colonized and developed watery, mucoid diarrhea within 2 to 11 days postinfection. Affected pigs all had moderate subacute mucosal colitis, with gross and histological changes similar to those previously reported in both natural and experimentally induced cases of PIS. Silver-stained histological sections of the colon and cecum from affected pigs demonstrated spirochetes within dilated intestinal crypts, where they were associated with neutrophilic exocytosis and mucus secretion. Sections from one pig infected with strain 95/1000 showed large numbers of spirochetes attached by one end to the colonic epithelium, a feature consistent with PIS. This study confirms the role of S. pilosicoli in the etiology of PIS and provides evidence that S. pilosicoli strains of human origin have pathogenic potential in an animal model.