They Might Sound Gross, but Intestinal Worms can Actually be Good for You

William Parker, Duke University

Intestinal worms have an incredibly bad reputation. The thought of them sneaking around inside our bodies and eating us from the inside is pretty unpleasant. But just 100 years ago, before toilets and running water were commonplace, everybody had regular exposure to intestinal worms. Thanks in part to modern plumbing, people in the industrialized world have now lost almost all of their worms, with the exception of occasional pinworms in some children.

Intestinal worms are properly called “helminths,” which most dictionaries will tell you are parasites. Exploiting their hosts, draining resources, sucking the life out of the body – that’s what parasites do, by definition. Indeed, many helminths, including the porcine tapeworm and the human hookworm, are known to cause disease and even death in the human population. Parasitic worms are still a big problem in some parts of the world.

But for decades, results coming out of lab after lab have shown that some kinds of helminths can be extremely beneficial to their host, and aren’t parasites at all.

These helpful helminths are mutualists, a type of organism that receives benefits from its host, and also provides benefits to the host.

For example, my lab, working with a Duke University colleague, Staci Bilbo, recently showed that the presence of helminths in pregnant rats protects the brains of the rat pups from inflammation. In other words, it seems that mom’s helminths can protect unborn babies. And that is just the tip of the iceberg for what these critters can do.

Worms may help with allergies and multiple sclerosis

Having worms isn’t necessarily bad for you. The largest randomized trial ever performed in human history – involving two million children in India – looked at how helminths affect health in places where humans naturally have them. The study showed that mass treatment with an effective deworming drug did not increase body weight or survival. Shockingly, the helminths didn’t seem to be doing any harm, since getting rid of them didn’t improve health.

So that study seemed to show the absence of harm; could these helminths actively be doing good?

In the past, scientists thought that increases in inflammatory diseases such as hay fever and multiple sclerosis in industrialized societies were due to keeping our created environments too clean. Thus the name “hygiene hypothesis.”

However, the true problem for our health is the loss of biodiversity from our body’s own ecosystem, a condition called “biome depletion.”

Missing mutualistic helminths is a key factor in this, and is apparently a major contributing factor to a very large swath of disease, including allergies and autoimmune conditions.

For instance, helminths have been found to protect laboratory animals from a wide range of allergies and autoimmune conditions. And recent findings suggest that many types of cancer can be reduced by helminths. The idea has been demonstrated by preventing colon cancer in rodents, and it is hoped that it will reduce the burden of cancer in humans by decreasing chronic inflammation, a condition that can give rise to cancer.

In controlled studies in humans, helminths were shown to halt the progression of relapsing remitting multiple sclerosis and effectively treat many individuals with inflammatory bowel disease without report of adverse side effects.