HYDATIDOSIS AND CYSTICERCOSIS — 3. INDUCED RESISTANCE TO THE LARVAL PHASE

Lambs from birth were reared in a tapeworm-free environment or on pasture contaminated with eggs of Taenia hydatigena. An examination for cysts at autopsy of some of the latter at 3 months of age revealed that they had ingested eggs. Eggs of T. hydatigena and T. ovis were fed at 6 months of age to lambs reared in the tapeworm-free environment and to some of those reared on the pasture. By comparing the number of cysts established at 9 months of age in the animals of each group, it was determined that those reared on the pasture had acquired some resistance to superinfection with T. hydatigena and infection with T. ovis. The remaining animals reared on the pasture were immunised (hyperimmunised) at 3 months of age by a parenteral injection of the eggs or embryos of T. hydatigena or T. ovis or both species. These animals were subsequently fed with the eggs of both species at 6 months of age. An examination of them for cysts at 9 months of age suggested that those immunisation procedures using the homologous organisms increased the resistance already acquired to superinfection with T. hydatigena and possibly also to that acquired to T. ovis. In addition, three of the procedures using homologous organisms appeared to induce regression of any cysts established from eggs of T. hydatigena ingested from the pasture prior to hyperimmunisation.