Studies in Trichinosis: I. Immunity to Reinfection in Mice Following a Single Light Infection

Abstract

Mice were given an initial infective dose of 100 Trichinella spiralis larvae, followed by a single reinfective dose of 800 larvae after either 10 days, 36 days or 3.5 mos. In one series, 300 larvae were administered 35 days after the initial infection. The immunity was studied during the entire course of the intestinal phase by counting the number and measuring the lengths of the adult worms. The muscular phase was studied by dilution counts of larvae after digestion in a mixture of pepsin and dilute HC1. Adult worm counts during the course of the intestinal phase did not show significant differences between reinfected and control animals when the number of larvae fed was 800, a dose which is just sublethal. When mice were reinfected with 300 larvae 35 days after initial infection, there was a loss of adult" worms beginning early in the 2d week of reinfection. Adult male and female worms were significantly shorter in length in re-infected animals. The uteri of the female worms appeared sparsely filled with eggs and embryos. The larval phase in the musculature for the 800 larvae infections indicated the lowest immunity after 10 days and the highest immunity after 36 days. The most striking manifestations of immunity were obtained in reinfections after 35 days with 300 larvae. It is believed that immunity after a single infection is manifested, not by rapid loss of fed larvae from the intestine, but, rather, by a stunting in growth of the worms in the intestine and a diminution of fecundity of the female worms.