Life-phase specific induction and expression of rapid expulsion in rats suckling Trichinella spiralis-infected dams.

Rat dams infected with 1000 Trichinella spiralis muscle larvae, 4 weeks prior to breeding, provided their suckling offspring with immunity to challenge with 200 muscle larvae at 2 weeks of age. The immunity was expressed in the elimination of 75-99% of the challenge dose within 24 hr. The intestinal worm burden did not decline significantly after the initial expulsion. Infected dams continued to protect their offspring during three breeding cycles, for as long as 26 weeks after infection. Immunity was conferred upon pups by dams that had been selectively immunized with the parenteral phase of the parasite's life cycle. Immunization with a drug-terminated enteral infection was ineffective as was enteral immunization followed by the parenteral phase. Further analysis revealed that rapid expulsion by pups was dependent on the number of mature muscle larvae recovered from dams immunized with NBL. By comparison, the expulsive capacity of the same dams was not improved by increasing the numbers of NBL within the range tested.