Protective immunity elicited by ultraviolet-irradiated third-stage infective hookworm (Necator americanus and Ancylostoma caninum) larvae in mice and hamsters.

The protective immunity elicited by ultraviolet-irradiated third-stage infective larvae of Necator americanus (UV-NaL3) and Ancylostoma caninum (UV-AcL3) was evaluated in laboratory mice (a non-permissive model) and hamsters (a permissive model). After optimizing the time of exposure to UV-irradiation, both oral and subcutaneous vaccination routes with UV-AcL3 in mice were explored. Oral vaccination was more effective at reducing the number of challenge AcL3 entering the lungs, whereas subcutaneous vaccination was more effective at blocking muscle entry. When UV-irradiated NaL3 and non-irradiated AcL3 were used as vaccines in hamsters, both of them were effective at reducing adult hookworm burdens. However, the length of protection afforded by UV-irradiated L3 was substantially greater than that resulting from immunization with non-irradiated L3. A single dose was less effective than multiple doses. The protective immunity elicited by UV-irradiated NaL3 given once every other week for a total of three immunizations was similar to that elicited by non-irradiated AcL3 given during the same schedule. Protection was not significantly affected by administering the L3 on a weekly basis for a total of three immunizations, even though the antibody titers were reduced using this schedule. These studies will facilitate the elucidation of the mechanisms underlying larval protection.