Experimental Ascaris suum infection in pigs. Serological response, eosinophilia in peripheral blood, occurrence of white spots in the liver and worm recovery from the intestine.

Experimental oral inoculation of pigs with infective A. suum eggs resulted in eosinophilia in the peripheral blood and a serum antibody response. When pigs were inoculated at 3 days of age the antibody response was depressed which is suggested to be due either to a protective effect of colostral antibodies or to an immunologic incompetence of the young pigs. Despite the use of isolated pens and strict hygienic measures it was difficult to obtain an Ascaris free environment for the experimental animals. The pathogenesis of white spots in the liver is assumed to represent an immune reaction by the host. Multiple white spots were demonstrated when pigs were inoculated with several egg doses provided the livers were examined 1--3 weeks after last inoculation. The rapid healing of white spots implies that the finding of many white spots in the liver at slaughter indicate a recent uptake of infective A. suum eggs. The finding of low intestinal worm burdens in the experimental pigs after repeated oral inoculations indicates a specific, acquired resistance. Resistance to A. suum in pigs is suggested to involve co-operation of the humoral and the cell mediated immune system and the parasite is eliminated both during migration by white spot formation in the liver and during the early prepatent period by expulsion from the gut.