Battling the Worms Inside You

An infectious disease specialist must tackle her patient's parasites head-on.

Head region the nematode Enterobius vermicularis, or human pinworm.

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.
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Something felt wrong: The pair of intestinal squatters made an odd combination indeed.

The neatnik side of my patient’s personality, his obvious preference for cleanliness and order, made his infestation especially poignant. No one likes the idea of harboring worms, but highly meticulous people suffer most of all. Finally, on top of everything else, the man was having on-and-off stomach pain. Before the colonoscopy, he’d had two emergency CT scans. When I asked why, he replied, “Frankly, doc, I was sure I had appendicitis.” Then he gingerly pressed his abdomen. “Sometimes I still do.”

Ouch, another curveball. In my experience, the localized tenderness in his lower right quadrant didn’t fit either parasite.

OK, enough second-guessing, I finally decided; there was no mystery about the next step. The ultimate proof of infection resided on microscope slides at another laboratory. After two or three phone calls, they were en route to my hospital for a second opinion.

A week later, our senior parasitology tech reported back. “Well, there’s no strongyloides in these specimens,” she said in a voice faintly tinged with regret, “but he’s sure loaded with pinworms, including really young larvae. I can see how the other folks got confused.” Soon a blood test negative for strongyloides confirmed her finding.

Now it was time to tell the patient. Not surprisingly, anger was his first reaction to the news that he’d been misdiagnosed. After all, by then he had spent many a sleepless night picturing evil strongyloides swarming his internal organs. His mood quickly brightened once he grasped that he had only pinworms, a far less ominous pathogen.

There was just one more mystery to solve: my patient’s continuing abdominal pain. Once in a while the attacks were so severe he felt he had no choice but to page me late at night. I was not about to rouse a surgeon from bed. But I started to wonder: Could a really bad case of pinworms mimic appendicitis? I went online and began to read.

Yes and no, according to recent research studies. In surveys published between 1991 and 2006, as many as 4 percent of surgically removed appendixes contained pinworms—an impressive statistic until one recalls that, in the United States alone, up to 20 million people are thought to harbor them. In other words, in terms of cause and effect, merely finding enterobius in an excised human appendix proves nothing.

But before abandoning my hypothesis altogether, I had one more mission—a trip to our medical school library. There, in a lonely corner of the stacks, I hit pay dirt: a 1950 paper titled “Pathology of Oxyuriasis: With Special Reference to Granulomas Due to the Presence of Oxyuris vermicularis (Enterobius vermicularis) and Its Ova in the Tissues,” by W. S. Symmers, an early 20th-century dean of tropical medicine pathologists.

In his masterful paper Symmers re­viewed the autopsy findings of patients with incidental pinworm infection diagnosed after death, describing several whose postmortem tissues revealed inflammatory nodules around worms that had “strayed from their usual haunts and died, and around ova deposited in the course of such anomalous wanderings.”

Symmers’s elegant prose provided just the insight I had been seeking. After all, who could say my patient’s gut had not harbored stray, wandering pinworms for decades since childhood—just as Symmers’s subjects had harbored their worms up to and beyond the grave? And surely, after so long an infestation, I reasoned, cast-off eggs, dying worms, and little patches of inflammation near the appendix would trigger periodic pain in at least a few pinworm victims, right?

It was hardly proof positive, but, thus armed, I felt ready to tell my patient two things. First of all, that he should be thankful that his colonoscopy had revealed his strange case. And second, that with modern drugs and the tincture of time, I believed his painful attacks would slowly subside.

I like to think I was right. In any event, over the past year his midnight pages have stopped.

Claire Panosian Dunavan, an infectious diseases specialist at UCLA Medical Center, is president of the American Society of Tropical Medicine and Hygiene. The cases described in Vital Signs are real, but the patients’ names and other details have been changed.