Response to repeated inoculations withAscaris suum eggs in pigs during the fattening period

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Abstract
This experimental study on pigs was designed to simulate natural, long-term exposure toAscaris suum under modern management conditions. Parasite kinetics were followed in pigs receivingA. suum eggs as repeated trickle inoculations at two dose levels beginning at a body weight of 25kg until their slaughter at 90kg (baconers). In pigs inoculated twice weekly with 500 eggs, there was an initial marked rise in the numbers of hepatic milk spots, but as early as around week 6 after the start of inoculations and until week 16, at which time the last pigs were slaughtered, the numbers of spots diminished drastically. In pigs receiving only 25 eggs twice weekly, low and moderately fluctuating numbers of spots were seen throughout the experiment. Larvae recoverable from the livers and lungs were observed mainly during the beginning of the experiment. Before patency, immature intestinal worms were found in moderate numbers that showed a rough positive correlation with the dose levels, but at the time at which adult worms started to appear, immature parasites could practically no longer be found. In all, only 10 of 40 pigs harbored adults, and 4 of these 10 pigs harbored, 80% of the total worm population. The results show that acquired dosedependent host responses toA. suum play an important role in regulating the worm population along the migratory route of the parasite and that the final burden of worms in the small intestine is dose-independent and highly variable.