Inhibited development of Obeliscoides cuniculi in rabbits: the effects of active and passive immunization and resumption of larval development

Rabbits were either actively or passively immunized against Obeliscoides cuniculi and challenged with 5 000 infective larvae (IL). Worm development was inhibited in actively immunized animals and worm egg production was impaired by administration of immune serum. Inhibited fourth stage larvae (L₄) from high-level infections (200 000 IL) and normal L₄ from low-level infections (4 000 IL) were transferred to actively immunized and normal rabbits. In both instances, large numbers of L₄ developed to maturity; however, a significant number of inhibited L₄ failed to resume development. Inhibition of larvae resulted in the development of fewer adult male than female worms, and the change in sex ratio was further accentuated in actively immunized recipients. Worm egg production was also reduced in actively immunized rabbits. These data indicate that host immune responses contribute to inhibition of O. cuniculi in rabbits and that worm egg production is also responsive to immunologic control.