Induction of immunity by transcolostrally-passed Strongyloides ransomi larvae in neonatal pigs.

Earlier studies had suggested that neonatal pigs that acquire infections of Strongyloides ransomi via the sow's milk fail to expel intestinal worms normally. Adult worm recoveries were compared from the intestines of normal and transcolostrally-infected neonatal pigs after a subcutaneous challenge inoculation of third-stage larve (L3) to determine whether a direct intestinal infection (via sow's colostrum) might affect resistance. Additionally, transcolostrally-infected pigs that had received an additional subcutaneous inoculation of L3 were reinoculated with L3, and the adult worm recoveries were compared to those of pigs immunized with only one subcutaneous inoculation of L3 to determine the effect of initial transcolostral infection on the development of protective immunity by this established procedure. The results showed that intestinal worms obtained transcolostrally can induce high resistance in pigs to reinfection by S. ransomi, and they do not affect the enhancement of protective immunity by a subcutaneous inoculation of L3. However, peripheral blood lymphocytes obtained from transcolostrally-infected pigs did not respond to larval antigens in vitro until after a subsequent subcutaneous inoculation of L3.