Expression of acquired immunity to the hookworm Ancylostoma ceylanicum in hamsters

Four experiments are described in which hamsters, initially exposed to primary infection with Ancylostoma ceylanicum , were given a homologous challenge and components of the secondary response were quantified and compared to relevant control groups. The initial establishment of the L3 larvae was not prevented in immunized hamsters but their growth was slowed and virtually all larvae were lost within a week of challenge, when the majority were still at the L4 stage of development. The loss of worms was associated with an accelerated mucosal mastocytosis and increased systemic antibody. Thus acquired immunity to hookworm larvae in this system acted on L3 and L4 stages, thereby preventing larvae from maturing in immunized animals. In contrast to primary infections, immunized hamsters responding to a challenge infection did not lose weight nor did they experience significant anaemia, because of the lack of adult worms. The secondary immune responses therefore prevented manifestation of hookworm disease among immunized‐challenged animals .