Persistence of Immunity Following Double Vaccination of Pups with X-Irradiated Ancylostoma caninum Larvae

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Abstract
A highly significant resistance to the establishment of a challenge of normal Ancylostoma caninum larvae, in groups of dog and bitch pups following double vaccination with X-irradiated larvae at 3 and 4 months of age, persisted in absence of further exposure to hookworm for at least 7 months after completion of the vaccination schedule. Towards the end of the 7-month period, resistance due to age of the host, as exhibited in the previously uninfected challenge control animals, augmented the immunity of the vaccinated animals against challenge worm establishment. The vaccinated animals at all ages were completely immune to the pathogenic effects of the challenge while older control animals were partially (at 8 months age) or completely (at 11 months) protected against these effects by age resistance per se. The control animals infected at 5 months of age were severely affected in terms of adverse clinical and hematologic changes. Vaccination with X-irradiated larvae stimulated an apparently maximal immunity which was not further improved by numerous small infections of normal larvae to the vaccinated dogs and bitches during the period between vaccination and the challenge at 11 months of age.