The worms usually resemble fish, maintaining their position in a stream with their heads pointing into the current. When they move, they do so against peristalsis in a spiral fashion, the middle of the body becoming coiled (Fig. 10.23). About 5% of ascarids are actually moving in this manner at any one time. When the worms move downwards, they bend backwards upon themselves, with their heads moving past their tails; only 3% of the worms are usually in this position (the "distal drift"). After treatment with an anthelmintic, the worms have their heads and tails at about the same level pointing downwards, as they are pushed through the intestine by peristalsis (Fig. 10.23). If they recover, they move upwards again in a normal, smooth curve towards the jejunum.

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Fig. 10.23. (A). Ascaris in the terminal ileum of a 52-year-old Latin American man. Note that the head and tail of the worm are at approximately the same level pointing downwards in a distal drift position typical of a dead or paralyzed worm after treatment with an anthelmintic. (Courtesy of Dr. William Thomas, McLean, Virginia.) (B). Poses of the Ascaris. The vast majority of ascarids (over 90%) are observed in the normal resting pose (A). They are unaffected by peristalsis and resemble fish keeping their position in a stream with their heads pointing into the current. (B) The advancing pose is identified by the coiled body of the worm. (C) The head and tail are both distal at approximately the same level. This pose is seen frequently after anthelmintics when the worms are propelled passively through the intestine by peristalsis. (From Dr. W.W. Davey, Companion to Surgery in Africa, E & S Livingstone Ltd., London, 1968.)

Adult Ascaris males and females can usually be distinguished by the characteristic hooked-shape of the posterior ends of the males. Coupling has only been observed in the uppermost segments of the jejunum. It is the tropism of the female worm to squirm through the coiled "tail" of the male that causes her to wander; this explains why it is mostly female worms that are extraintestinal.

Lagundoye analyzed radiographs of 200 patients in Ibadan, Nigeria, after they had ingested barium and found Ascaris in the small bowel in 53 cases (26.5%). Of these patients, 48 (92%) showed a disordered small bowel mucosal pattern in the region of the worms and occasionally farther away. The most common abnormality was coarsening of the mucosal folds. (See Figs. 10.20B and 10.21). It is theorized that toxic products or allergens liberated by the Ascaris may cause: (1) local changes due to their direct action on the small bowel mucosa or indirectly through an allergic or hypersensitivity reaction, and (2) distant changes which may be due to the absorption of these products into the submucosal lymphatics, whose engorgement may produce a disordered mucosal pattern.