US researchers have successfully treated monkeys with chronic diarrhea using parasitic worms that seem to work by restoring balance in gut bacteria. Their findings strengthen the case for developing and testing probiotic worm therapy for people with inflammatory bowel diseases like colitis.

Colitis and other inflammatory bowel diseases are caused by the immune system wrongly targeting bacteria in the gut and upsetting the balance of bacterial communities (a condition known as dysbiosis). This can lead to very unpleasant symptoms that diminish quality of life, such as diarrhea, vomiting, abdominal pain, and rectal bleeding.

In this latest study, the researchers used monkeys with a condition similar to colitis in humans, which affects some 1.4 million Americans. They tested the effect of giving the monkeys microscopic parasite worm eggs and found they may improve symptoms of colitis by restoring gut bacteria to a healthy state.

P’ng Loke, assistant professor of microbiology at New York University (NYU) Langone Medical Center, who led the study, says in a statement:

“The idea for treating colitis with worms is not new, but how this therapy might work remains unclear.”

He and his colleagues write about their study in the 15 November issue of the open access online journal PLOS Pathogens.

Inflammatory bowel diseases like colitis are rare in developing countries where infection with microscopic parasite worms (helminths) is endemic. This has led scientists to propose that these parasitic worms may offer protection against such diseases.

Studies that have modelled human autoimmune diseases in animals suggest the worms suppress inflammation, and clinical trials that have tested parasitic worm therapy in humans indicate they may benefit people with inflammatory bowel diseases.

One theory is that because the immune system of mammals has co-evolved with parasitic worms over millions of years, the worms have developed very effective ways of evading the host defences. The result is that the immune system has come to rely on these worms as a way to maintain balance in gut bacteria and keep us healthy.

This latest study may have discovered evidence to support this idea, as Loke explains:

“Our findings suggest that exposure to helminths may improve symptoms by restoring the balance to the microbial communities that are attached to the intestinal wall.”

Young monkeys in captivity often spontaneously develop chronic diarrhea that is difficult to treat.

For their study, the researchers gave 5 monkeys with chronic diarrhea an oral dose of 1,000 microscopic helminth eggs, having first collected gut tissue samples, via colonoscopy.

They collected further gut tissue samples 14 weeks after treatment. They also took samples from two age-matched healthy controls.

The results showed that samples from the sick monkeys, both before and after treatment, had many more attached bacteria than healthy monkeys and had a completely different balance of bacterial types (showing signs of dysbiosis).

However, the types of bacteria in the samples taken from the sick monkeys after treatment were much more similar to those of the healthy monkeys than they were before the treatment.

Also, after treatment, four of the five sick monkeys had less diarrhea and started to put on weight.

The researchers are already recruting patients to take part in a clinical trial to treat ulcerative colitis with pig parasite eggs, also known as hookworms, or Trichuris suis ova (TSO).

They are using TSO because the US Food and Drug Administriation (FDA) has certified their use for clinical trials. TSO can be produced under pathogen-free conditions and can’t spread from person to person.

Written by Catharine Paddock PhD