Metabolic and Somatic Antigens in the Determination of the Response of Rabbits to Graded Infections with Trichinella spiralis

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Abstract
Several groups of rabbits were infected with graded doses of Trichinella larvae varying from 500 to 400,000 larvae. The 50% lethal dose under the experimental conditions was 88,600. The size of inoculum had a direct relation to the percent mortality in each group and an inverse relation to the average length of survival. Infected rabbits were bled weekly, and the sera were tested by the bentonite flocculation reaction using metabolic and purified somatic antigens. With both antigens, the time interval from inoculation to the first positive serology was inversely related to the size of inoculum. The geometric mean of the titer increased rapidly from the first weeks following inoculation up to about 2 months and thereafter it decreased gradually. The peak titer was directly related to the size of inoculum and was higher with the metabolic antigen. Although a great similarity of results with the 2 antigens was observed, the metabolic antigen conferred to the flocculation test a somewhat greater sensitivity. This greater sensitivity was observed in experimentally infected rabbits, in rabbits artificially immunized with somatic or metabolic antigens, and in those which were infected with the intestinal phase of infection alone. The metabolic antigen did not give a more sensitive test with sera from rabbits infected with the muscular phase alone.