The trillions of
bacteria that reside in the gastrointestinal tract have an enormous
impact on human health and disease. But the effects of other types of
microorganisms that live in the gut, such as the unicellular eukaryotes
known as protozoans, are less well understood.
Though some protozoan
species, which are part of the protist kingdom of life, cause diseases
like malaria and leishmaniasis, the protozoa that commonly live in the
gut are generally thought to be harmless.
‘Mice infected with the common gut parasite Tritrichomonas muris are at an increased risk of developing inflammatory colitis, revealed researchers.’
Researchers from the University of Toronto have discovered that mice infected with the common gut parasite Tritrichomonas muris
are at an increased risk of developing inflammatory colitis. Their findings, which have been published online in The Journal of Experimental Medicine
expand the type of gut-resident microorganism that can affect the
health of their host and suggest that related parasites may cause
gastrointestinal disease in humans.
While studying the inflammatory mechanisms underlying colitis in rodents, a team of researchers led by Dana Philpott and Thierry Mallevaey
realized that their laboratory mice were more susceptible to developing
the disease if their intestines were already infected with the
protozoan Tritrichomonas muris
This parasite is commonly found
in the intestines of mice, and the researchers observed that its
presence raised the levels of pro-inflammatory T cells and cytokines in
the host animal's gut. These inflammatory factors may "prime" the
intestinal tissue to become inflamed, leaving it more susceptible to
A recent study published in Cell
revealed that, while the related parasite Tritrichomonas musculis
makes the intestine susceptible to both colitis and colorectal cancer,
it induces an immune response that protects mice against Salmonella
infection. This may be why host animals tolerate protozoans such as T. muris
living in their intestines.
Several species of protozoa reside in the
human gut, and some of them are prevalent in patients with
gastrointestinal disease, suggesting that similar host-parasite
interactions could affect human health. "Our findings highlight the need
for a better understanding of cross-kingdom interactions between host
and protozoa within the gastrointestinal tract," says Philpott.