Woman with Diarrhea and a Worm

Diagnosis: Horsehair worm. The horsehair worm (figure 1) derives its name from an uncanny resemblance to the hair of a horse’s tail and belongs to the phylum Nematomorpha [1]. Included in this phylum are the genera Gordius, Paragordius, and others. The larvae are parasitic in insects, such as grasshoppers, beetles, and cockroaches. The adult worms emerge from the insect’s body when the insect goes to a water source. Adult worms are free-living in water, slender, and wiry; they grow up to 50 cm in length and 0.1–0.15 cm in thickness. Many exhibit a twisting motion, and they may loop themselves into loose knots (thus, they are also known as the “Gordian worm”). Because they are devoid of an alimentary system, they absorb nutrients from their surroundings. The adult worm may be found in toilets, birdbaths, swimming pools, and sinks or on fresh vegetables; they may also emerge when an insect is crushed. It is important to be aware of the horsehair worm, because they are sometimes brought to physicians’ offices with the concern that they came from a child or a pet. These worms may also be seen as artifacts in stool specimens in microbiology laboratories. However, they are not considered to be pathogenic to humans, even in the rare instances involving documented passage through the body of a human.