Trichinella spiralis: expression of rapid expulsion in rats exposed to an abbreviated enteral infection.

Rats infected with Trichinella spiralis for the first week of the enteral infectious cycle displayed a strong rapid expulsion reaction during a challenge infection. The response was induced with equal facility in animals given low or high immunizing doses of infectious larvae (500 to 5000 larvae). Large challenge infections resulted in a 10–15% reduction in the efficiency of rejection as assessed 24 hr after challenge. Rats became primed to express rapid expulsion within the first week of primary infection whether the infection remained patent or not. However, maximum effectiveness was not realized until the second week after the initial infection. Once induced, the capacity to express rapid expulsion persisted for 6 weeks after the primary infection. Immunized hosts were capable of resisting two challenge infections spaced by periods of from 12 to 72 hr. This finding suggests that a mediator is not consumed by the initial response.