Immunization against Nippostrongylus brasiliensis in the rat. A study on the use of antigen extracted from adult parasites and the parameters which influence the level of protection.

It was found that protective immunity in excess of 90% reduction in worm burden could be stimulated against Nippostrongylus brasiliensis in rats by using an extract of adult Nippostrongylus worms. The level of protection achieved was influenced by several factors. Thus, the use of Bordetella pertussis as adjuvant significantly increased the level of protection which, in addition, was shown to be influenced by the amount of worm antigen used. Furthermore, antigen administered in multiple doses was more effective than a single inoculum and, when using such a regime, the interval between doses was also found to be critical. The route of antigen administration was important and, while protection was achieved by subcutaneous and oral administration, the intraperitoneal route was the most effective. Using the optimal immunization regime of 3 doses of 5 mg worm protein and 4 x 10(10( B. pertussis organisms, as adjuvant, levels of protective immunity in excess of 90% reduction in worm burden were shown to exist for at least 60 days after the last dose. It was found that adult worm extracts did not stimulate any obvious immunity against larval forms of N. brasiliensis.