ASCARIS-SUUM - A REVISION OF ITS EARLY MIGRATORY PATH AND IMPLICATIONS FOR HUMAN ASCARIASIS

During the course of carrying out studies on the role of intestinal im munity in blocking the migration of larval Ascaris suum in the pig, it was discovered that the prevailing understanding of larval penetratio n sites was at variance with our observations. Therefore, a detailed i nvestigation of the migration of A. suum L2 larvae through the intesti ne was initiated. The results demonstrate that the L2 larvae invade al most exclusively che wall of the pig cecum and colon and not the small intestine as is generally believed. The larvae were recovered from th e mucosa of the cecum and colon as early as 3 hr postinoculation (PI) with infective eggs and were recovered from the liver by 6 hr PI. The maximal recovery of larvae (total larvae and larval/g of mucosa) from the intestinal mucosa occurred between 6 and 12 hr PI; by 24 hr PI, vi rtually all of the larvae had disappeared from the mucosa. These obser vations correct a common misunderstanding of this aspect of the life c ycle of A. suum in the pig, and they raise 2 issues related to the bio logy and pathogenesis of Ascaris in humans. What is the actual migrato ry and development behavior of Ascaris lumbricoides and A. suum in hum ans and the potential risk for liver lesions? Most authors, in describ ing the life cycle of A. lumbricoides, either ignore or discount a pos sible obligatory liver stage of development, and, consequently, the po tential for lesion formation similar to that which occurs in pigs infe cted with A. suum. This issue takes on added importance with the growi ng evidence that A. suum is an important zoonoses.