Establishment of Ascaris suum in the pig: Development of immunity following a single primary infection

Development of immunity after a single primary infection of Ascaris suum in pigs was investigated with regard to the worm population dynamics of a sup erimposed A. suum infection, host immune response and gross river pathologi cal changes. Group A was given a primary infection of 60000 infective A. su um eggs and group B was left uninfected. Four weeks later both groups A and B were inoculated with 1 000 A. suum eggs, and subgroups were slaughtered 7, 14 and 21 days post challenge infection (p.c.i.). An uninfected control group C was slaughtered on day 21 p.c.i. The challenge worm recovery in gro up A was reduced compared to group B by 12%, 50% and 75% on day 7, 14 and 2 1 days p.c.i., respectively In both groups was the expulsion of worms initi ated between day 14 and 21 p.c.i. However, in group A the worms were recove red more posteriorly in the small intestine and 21 days p.c.i. the mean wor m length was significantly shorter than in group B (p = 0.01). The results above were associated with significantly higher (p<0.05) antibody response and higher eosinophil counts in group A compared to group B. The present re sults suggest that the larval growth and survival of a challenge infection are decreased, probably due to higher antibody and eosinophil attack during the migratory phase.