Mild infections with worms can go largely unnoticed. People with more serious infections can have bloody stools and other symptoms.
After hearing about the man's trip to Thailand, Loke and Cadwell decided to investigate.
Initially, they wanted to see if they could cure mice. To answer this question, scientists used specialized mice that mimic the human symptoms of Crohn's disease. These mice have damaged intestinal cells and lack most of the protective mucus that coats the intestine.
Loke and Caldwell suspected the helminths alter the bacterial population in the intestine. The intestine is a lot like a bustling metropolitan city, but populated with bacteria, not people.
Just like a city, some of the intestine's residents are helpful, and some harmful. The ratio of helpful to harmful bacteria plays a role in the development of many diseases, including Crohn's. The researchers wanted to see if feeding parasitic worm eggs to mice would decrease the number of bad bacteria that are associated with Crohn's and increase the numbers of helpful bacteria.
When the researchers fed the mice worm eggs, the population of good bacteria, called Clostridiales, shot up. In contrast the amount of bad bacteria, called Bacteroides, went down. The mice also had reduced inflammation in the gut, an increase in the helpful mucus-producing cells, as well as reduction in harmful intestinal abscesses. Loke and Cadwell published their findings Thursday in the journal Science.
Great for mice, but what about people?
The scientists weren't ready to start feeding worm eggs to sick people, so they tried an indirect research approach. They surveyed a small population in Malaysia, called the Orang Asli tribe. The Orang Asli experience virtually no inflammatory bowel diseases, and a high percentage of them have chronic parasitic worm infections.
Loke and Cadwell wanted to know: If we remove their worms, will we see an increase in harmful bacteria? The answer turned out to be yes.
Before the worms were removed, the tribe members had higher levels of helpful bacteria and lower levels of harmful bacteria. After taking a deworming drug, that healthy ratio was flipped. Cadwell and colleagues concluded that parasitic worms increase the population of beneficial bacteria in both humans and mice.
The specialized mice that the researchers use to study Crohn's have a deficiency in a protein called Nod2. Some Crohn's patients (about 25 to 30 percent) also have this deficiency.