Head region the nematode Enterobius vermicularis, or human pinworm.
Wikimedia Commons
Not long ago I received two messages at my medical office about an earthy problem. One was from a patient who said a colonoscopy had turned up a small herd of tiny white worms in his gut. Needless to say, he was not pleased to learn that he was sharing his cecum (the segment of bowel from which the appendix dangles as a thin sac) with a pack of nematodes. I agreed to see him as soon as possible.
The next message was from the doctor who had performed the colonoscopy. “Urgent!” he texted. “Need help with enterobius and strongyloides.”
Now we’re getting somewhere, I thought. To a Latin-loving parasite specialist like myself, the exotic names were familiar, as were the necessary treatments. But deep down, something felt wrong. It wasn’t the anxiety surrounding the worm sighting. That seemed natural enough. No, I decided, it was the actual pair of intestinal squatters. An odd combination indeed.
Enterobius vermicularis, or pinworm, is a surprisingly common stowaway in the bowels of temperate-world residents, especially children. Ask any veteran North American schoolteacher: At some time or another, most have dealt with a fidgety youngster with the threadlike pest. Fortunately, aside from an itchy bottom, sufferers rarely experience serious harm. And pinworms are easily banished. A few pills and they’re history.
On the other hand, the tropical parasite Strongyloides stercoralis is, without question, one of the most dangerous of intestinal nematodes that affect humans. Reason number one: The minuscule, soilborne pathogens invade an entry point such as bare feet, then move through blood vessels and lung tissue on their way to the human gut, and they sometimes repeat their journey over and over, cycling between the gut and the rest of the body. Reason number two: Minus treatment, strongyloides can stay in the host body for a lifetime. Reason number three: In immunosuppressed patients, the tiny creatures go wild. In the worst-case scenario, their zigzagging offspring wreak mayhem and can even cause death, usually from overwhelming bacterial infections that follow in their wake.
As I mulled the surprising pair of helminths, my mind registered one more puzzling detail: their dissimilar sizes. As any parasitology textbook can attest, strongyloides are a heck of a lot smaller than pinworms—so small that they are generally not visible through the fiber-optic scope used by a gastroenterologist for a colonoscopy.
My puzzlement continued later, after I interviewed the patient. As far as I could tell, his opportunity to encounter strongyloides was close to nil. The final Sherlock Holmesian clue involved his feet. On the rare times when he vacationed in the tropics, he always wore waterproof beach shoes. Strongyloides larvae usually enter humans by penetrating bare feet because the infective larvae are present in the soil. Occasionally infection occurs via ingestion.
