Induction of protective immunity to Strongyloides ransomi in pigs.

Pigs inoculated once or twice with infective Strongyloides ransomi larvae (L3) developed a strong protective immunity to challenge exposure. Intestinal expulsion of adult worms resulting from initial infection occurred 3 to 4 weeks after inoculation; worm loss reached 68% by 52 days after inoculation. Necropsy of pigs at various times after challenge exposure with infective L3 revealed that the majority of migrating L3 were eliminated before reaching the intestine; based on parasitic recoveries from the lung, the reduction was manifested as early as 48 hours after challenge exposure, Evidence for enhanced migration of L3 to the fat tissue in immune pigs could not be detected. Data indicate that infective L3 possess functional antigens capable of inducing protective immunity. Treatment of infected pigs with ivermectin was effective in removing arrested L3 in the subventral fat; 85% of these larvae were eliminated in 3 weeks. The role of milk-transmitted arrested L3 in the immunology of porcine strongyloidiasis is discussed.