Iatrogenic Trichuris suis Infection

To the Editor.—We compliment Kradin et al1 for their interesting article “Iatrogenic Trichuris suis Infection in a Patient With Crohn Disease.” They have convincingly demonstrated T suis in the colonic tissue of a patient following treatment with Trichuris ova.

Their findings show that the larvae of T suis in fact were invasive in the human host. In the normal host, trichurid larvae that hatch from eggs in the small intestine don't travel over the surface to the large intestine. In order to get there they penetrate the mucosa, where they wander for a time in the lamina propria, undergo several larval moults, and then come to the mucosal surface where they protrude their posterior extremities.2 The adult worm remains fixed with its anterior (filiform) end embedded while the thicker posterior part of the body extends into the lumen of the bowel. The findings of Kradin et al (including the presence of a mature adult male worm) confirm that T suis undergoes a similar cycle in humans. So, the idea that T suis is noninvasive in the human host is false.

If some of the larvae developed through successive stages in the lamina propria, what happened to the others? Did they perish, are there more still present in the lamina propria, retarded in their movements to the surface in this foreign host, and have others migrated beyond the mucosa? When T suis was identified in wild boars (Sus scrofa), a foreign host for them, they had traveled an aberrant pathway to as far as the kidneys.3 Will some T suis given as treatment to human patients find their way to the kidney or retina or central nervous system? Pathologists encountering nematodes at unusual body sites in inflammatory bowel disease patients should entertain the possibility that the patient might have iatrogenic larva migrans.

Summers et al choose to report that these larvae are not invasive. This article and the literature make it clear that this is not so.4 It is not clear why the present authors chose to reference Beer's 1976 article5 but failed to notice his 1973 article2 in which the 13-day invasive phase of these parasites is described.