Experimental Ascaris suum infection in the pig: protective memory responseafter three immunizations and effect of intestinal adult worm population

The protective immune response to larval migration in pigs, with or without adult intestinal worm populations, 10 weeks after 3 weekly Ascaris suum in oculations, was studied in 45 pigs. Controlled adult worm populations were achieved by oral transfer of 10 adult worms to previously immunized pigs af ter anthelmintic drenching. A significant reduction in larval recovery from lungs on day 7, and small intestine on day 14, was observed in immunized p igs compared with previously uninfected control pigs after challenge inocul ation. The strong anamnestic response to larval migration was characterized by blood eosinophilia and specific immune responses measured by peripheral blood enzyme-linked immunospot and immunosorbent assays using larval excre tory-secretory products and adult body fluid as well as Western blotting wi th a panel of stage-specific A. suum antigens. Immune detection of a previo usly unreported 10 kDa band, specific to the L2 larval stage and egg hatch fluid, emerged in all pigs after challenge, while the major adult body flui d constituent, ABA-1, remained unrecognized. No significant effect of an in testinal adult worm burden on the larval recovery after a challenge inocula tion or on the immune response before or after challenge inoculation could be detected. These results indicate that a significant protective memory im mune response to A. suum challenge inoculation can be induced in pigs, and that this protective immunity is not significantly modulated by the presenc e of adult parasites in the gut.