The protective properties of various second-stage larval and egg preparations of Ascaris suum were evaluated in mice. Groups of mice were injected by several “immunization” schedules with (1) lyophilized and live embryonated eggs, (2) lyophilized and live hatched second-stage larvae, (3) supernate of ground embryonated eggs, (4) live embryonated eggs per os and (5) excretions and secretions of second-stage larvae. Immunization also was attempted by planting diffusion chambers containing live second-stage larvae intraperitoneally in mice.
The criterion of immunity was a significantly lower number of larvae in the lungs of mice 8 days after a challenge infection by embryonated eggs by mouth. The results show that under the conditions of the experiment, a marked protective immunity was produced when live larvae were used for the immunization. Immunization with excretions and secretions of second-stage larvae resulted in a significant immunity, as did implanting diffusion chambers containing second-stage larvae. However, the degree of resistance produced by these latter two methods was not as high as that produced by actual infection.