Once germ theory gained acceptance and the mechanics of infection became known, microorganisms—and the filth they breed in, and the insects that deliver them—became targets of military campaigns. Suddenly there were Fly Control Units, sanitation officers, military entomologists. The US military has been involved in most of the major advances in preventing, treating, and understanding diarrheal disease. Cairo’s NAMRU-3, the parent unit of Mark Riddle’s humble container lab in Djibouti, has a four-star antidiarrheal pedigree. Its first director, Navy Captain Robert A. Phillips, figured out that adding glucose to rehydration fluids enhances intestinal absorption of salts and water. This meant rehydration could be achieved by drinking the fluids rather than making one’s way to a clinic to have them administered intravenously. This has been a lifesaver not only for people who fight in remote, medically underserved areas but for people who live there. A 1978 Lancet editorial called Phillips’s discovery “potentially the most important medical advance this century.”
The full name of Riddle’s study is Trial Evaluating Ambulatory Treatment of Travelers’ Diarrhea (TrEAT TD).* “Travelers’ diarrhea” is another catch-all term. Most of it—at least 80 percent—is bacterial, with 5 to 10 percent viral (vomit typically joining the waterworks here) and a miscellaneous percentage from protozoa like amoeba or giardia. All of it is caused by contaminated food or water. There used to be a separate category called “military diarrhea” (military referring to the patients, not the explosive nature of their evacuations), but if you look at the responsible pathogens, the breakdown is almost the same. Military diarrhea is travelers’ diarrhea, because service members are travelers—in places where you don’t want to be drinking the water. A survey conducted by Riddle, David Tribble,? and others with the US Naval Medical Research Center revealed that from 2003 to 2004, 30 to 35 percent of military personnel in combat in Iraq experienced situations where they lacked access to safe food and water. In the early days of a conflict especially, combatants are like backwater backpackers, crapping in the dirt and waving the flies off whatever food the locals are peddling. In that same survey, 77 percent of combatants in Iraq and 54 percent in Afghanistan came down with diarrhea. Forty percent of the cases were serious enough that the person sought medical help.
For every person who shows up at morning sick call, four tough it out. Riddle would like to know why. The average bout of travelers’ diarrhea lasts three to five days. Why endure this, when some of the new antibiotics, Riddle’s data show, can have you back to normal in four to twelve hours? He’s been asking around, mostly at mealtimes. The tables in the hangar-size Dorie? are arranged church basement–style, in long rows, so there’s always a friendly stranger across from you or at your elbow, someone new with whom to chat about loose bowel movements while you eat.
Riddle gets right into it this morning with the man to his left. The uniform identifies the man as a Marine sergeant, last name Robinson. “I’m in the Navy,” Riddle is saying, “and we’re looking at simplified treatment regimens for travelers’ diarrhea. We’re finding that a single dose of antibiotic and an antimotility . . .”
Robinson looks up from his eggs. “Anti—?”
“Like Imodium,” I offer. “Stops you up.”
“Oh, absolutely not. You do not want to mess with Nature like that.” Robinson has the booming vocals and commanding bullnecked air of the actor Ving Rhames. One imagines Riddle going straight over to the lab after breakfast and tossing his data in the trash—What was I thinking?
“You have something bad in you, bad water or what have you? You got to pass it.” It’s like discussing diarrhea with the Giant Voice. “Defeat the purpose if you mess with that.”
We’ve been hearing this a lot. People think diarrhea is the body’s attempt to rid itself of invaders, or to flush out the toxins they produce. They won’t take an antimotility drug like Imodium because they think it interferes with the purge. But diarrhea is not something you are doing to pathogens; it is something they are doing to you. In varied and dastardly ways. Shigella and campylobacter, two common causes of bacterial dysentery, wield a toxin-delivering “secretion apparatus”—a hypodermic-cum-bayonet that injects toxins into cells in the intestinal lining, killing them and causing the fluid inside them to spill out. That spillage is part of the watery-stool scenario, but there’s more! With enough of those cells out of commission, the large bowel can no longer perform its duty as an absorber of water. Instead of food waste getting drier and more solid as it moves along the gastrointestinal tract, it stays liquid all the way along. The bacterium called enteroaggregative E. coli produces the same effect, in a different manner. It becomes a living cling wrap, a bacterial phalanx that coats the intestine and blocks absorption. Vibrio cholera and enterotoxigenic E. coli, or ETEC, inflict chemical weapons: Both produce a toxin that hijacks the pump that maintains cellular homeostasis. The commandeered pump begins pulling water out of cells faster than patients can replace it by drinking.§
Why do these creatures do this to us? Is there an evolutionary motive? Sure, says Riddle. There always is. By causing humans to produce liquid feces, feces that splatter and flow and coat a larger surface area, a pathogen speeds its spread. Cover the world! The bacterium that causes cholera is especially proficient. Cholera patients decant as much as five gallons of liquid a day. The efflux is so torrential that one of Dr. Phillips’s Navy colleagues was inspired to invent the cholera cot, an army-style cot with a hole cut out under the buttocks. (Bucket sold separately.) The cots, still made today, allow patients to “go to the bathroom without leaving the bed,” writes specialneedscots.com, taking euphemism into the realm of quantum physics.
Besides, enteric bacteria are not easily flushed out. They’ve evolved ways to hang on in the deluge. ETEC—the bacteria behind as much as half of all travelers’ diarrhea—are equipped with a hairlike grappling hook called a longus, which they use to pull themselves close to a cell wall. On receipt of a chemoelectrical signal from the cell, the bacteria sprout springy hairs called fimbriae, with suction cups at their ends. Your immune system, for its part, has more sophisticated defenses than simply hosing down the premises. It starts cranking out specially designed antibodies. One might target the suction cups and keep them from adhering. Another might gum up the longus or disable the toxin.