Alternative Migration Routes of Ascaris suum in the Pig

Experiments were conducted to investigate possible alternative routes of extraintestinal migration of Ascaris suum larvae in the pig. Pigs were infected with A. suum via injection of newly hatched larvae into cecal veins (IV), into cecal lymph nodes (LN), or intraperitoneally (IP), and control animals were inoculated orally with infective eggs (PO). Two pigs per inoculation route were necropsied on days 1, 4, and 13 postinoculation. The numbers of liver lesions and the percentage of larvae recovered was considerably greater in pigs inoculated IV or PO on each necropsy day. However, irrespective of inoculation route, at least a proportion of larvae passed through the livers and were able to complete migration to the small intestine by day 13. The results indicate that larval penetration of the intestinal wall is not necessary for liver–lung migration and that passage through the liver may be favorable for migrating A. suum larvae, although a delayed arrival in the small intestine cannot be ruled out for larvae following alternative routes.