When Jasper Lawrence receives a customer order, he consults his supply closet: his toilet. The founder of a Europe-based start-up, Autoimmune Therapies, Lawrence sells hookworms and whipworms he meticulously harvests from his own feces.

Each dose is individually prepared. For hookworms, Lawrence buries his waste in sand, collects the larvae that migrate to the surface, bathes them in antimicrobials and antibiotics, and finally packages them to be shipped around the world.Preparing a treatment of whipworms, parasitic roundworms that similarly invade the digestive tract, is more complex—worm ova need to be separated with a micron-sized filter before they can be packaged.

If you’d like to join the 240 plus customers Lawrence has served, all this can be yours for $2,900 per dose. However, you’ll have to leave the United States to collect and ingest your new microbial tenants. Helminthic therapy—the deliberate infestation of the gut with parasites like hookworms and whipworms—is illegal to purchase in the United States.

The controversial form of treatment is based on the hygiene hypothesis, first proposed by British epidemiologist David Strachan in 1989. The idea is that modern society’s obsession with cleanliness is depriving the body of its natural development of immune defenses.

Advocates for helminthic therapy believe that disorders such as inflammatory bowel disease and asthma occur because, in developed countries, good sewage treatment has eradicated gastrointestinal microbes that have an important influence on our immune system.

But how exactly could tiny creatures in our gut interact with our immune system in a way that benefits us? Some doctors think that helminths suppress immune response, and in doing so, prevent allergic reactions.

An allergy is an immune system overreaction to normally harmless environmental molecules like pollen and pet dander. The exact cause of allergies is still a mystery, said University of Iowa gastroenterologist Dr. David Elliott, who is supervising clinical trials on worm therapy. What does seem apparent, according to Elliott, is that helminths, which can be subject to immune system attack, pump out a protective cocktail of chemicals that dampens immune response. When the immune system is slowed, allergic reactions and other inflammatory diseases become less frequent.

Lawrence—who suffered from severe allergies throughout his life—caught wind of helminthic therapy by chance, sparking an obsession that in 2004 led him to the public sewers of Cameroon on a quest for hookworms. He returned home with a legion of parasitic invaders in his gut and claims he immediately noticed a difference—no puffy eyes, no runny nose…no allergies.

Many experts aren’t buying it. Dr. Peter Hotez of George Washington University, who is working to develop a hookworm vaccine, points out that helminthic disease is one of the most common problems of “the poorest of the poor”—the 1.4 billion people around the world who have no income at all. Parasites such as hookworms debilitate those infected and promote poverty, Hotez said. Hookworm infection in developing countries causes anemia in children, complications for pregnant women, and leads to a chronic loss of economic productivity by sapping the strength of those infected, Hotez described in an article with a team of medical experts published in PLoS Neglected Tropical Diseases journal in 2008.

Deliberate infection with helminths “makes absolutely no sense at all,” Hotez said. “The whole thing is based on flawed reasoning.” The hygiene hypothesis, he said, ignores the fact that high rates of helminthic infection still occur in the U.S. For example, 25 percent of African Americans living in poverty have the toxicara parasite. “I don’t think allergies in the West have anything to do with the absence of hookworms,” he said.

In fact, whipworm infection is actually the leading global cause of inflammatory bowel disease, and allergies have been linked to toxicara infestation in American cities, Hotez pointed out.

But Elliott argues that real-world examples indicate differently. South Korea recently launched a major helminth eradication program, and shortly thereafter, he said, Crohn’s disease appeared on the scene. Hotez counters, however, that an increase in inflammatory bowel diseases would also reflect “massive changes” in a variety of factors such as diet, lifestyle, and gut flora that also accompany development.

For “villages in the middle of nowhere” suffering as a result of hookworm infection, Elliott supports vaccine development. He points out, though, that individuals in need of vaccination also tend to have low intakes of protein and iron— two dietary deficiencies that lead to problems from otherwise “relatively benign” parasites.

Hotez, however, believes helminthic therapy is an unsafe practice whose risks do not outweigh the benefits.

Worm supplier Jasper Lawrence acknowledged that some of his clients do develop mild symptoms such as diarrhea and fatigue when first infected, but said those symptoms soon pass. The biggest risk associated with helminthic therapy, he said, is that “it’s likely 25 to 30 percent of your friends are going to think you’re completely nuts if you admit to it.”

The federal government might think you were nuts, too. In October 2009, the U.S. Food and Drug Administration defined hookworms as an Investigational New Drug, meaning that license applications, clinical trials, and regulation would be required to sell hookworms—all of which Lawrence lacked. Currently, no one is licensed to sell worms for therapy in the United States, and FDA representative Paul Richards said that that the agency cannot project the future timing of any such approvals.

Despite the FDA’s decision, Lawrence hasn’t stopped selling his worms—he’s just moved. “I had to leave America where I lived for 23 years,” he said of his recent move to Europe where he continues to provide hookworms to patients outside of the U.S.

Whether Lawrence will ever be able to sell worms from the U.S. will depend on the outcome of clinical trials like the one Iowa’s Elliott is conducting. “The studies are marching along,” Elliott said.

Elliott’s preliminary results show that helminths can be used to keep autoimmune responses at bay. The conditions of 27 of 54 patients with Crohn’s disease improved when infected with whipworms, according to a study Elliott published in 2005 in Current Opinion in Gastroenterology. More recently, a study led by immunologist P’ng Loke published December 2010 in Science Translational Medicine followed the cellular changes in the intestinal lining of an ulcerative colitis patient who treated himself with whipworms. The study found that whipworm infection resulted in a thickening of the mucus lining of the intestines, sending the disease into remission.

Other proponents of helminthic therapy have been less successful, however. Immunologist David Pritchard at the University of Nottingham published a 2009 paper in the American Journal of Tropical Medicine and Hygiene stating that no significant relationship was found between patients infected with hookworms and their immune response. Pritchard, who declined to comment on his work, concluded in his paper that future trials using a greater number of hookworms to test for immune response could yield positive results.

Elliott’s and others’ research represents only the beginning of a lengthy process of testing and refining the treatment before it could be available for FDA endorsement—three years at the very soonest. With trials taking place at the University of Wisconsin-Madison, the University of California-San Francisco, and in various European universities, though, parasites may yet invade future prescriptions.