Bacteria and their tiny microbial comrades may not be only immune-modulators calling our intestinal tracts home – it now appears that the common whipworm, or Trichuris, a goliath by comparison, plays a far more important role in our health and well-being than ever realized.
A new study shows that whipworm eggs are unable to hatch without the help of gut bacteria and this indicates a long evolutionary relationship between the worms, bacteria and their mammalian hosts; it also strongly suggests that the worms, like bacteria, are intimately involved with their host’s immunity.
A Bit about Parasitic Worms
Whipworms are a very successful group of parasitic nematodes infecting a wide range of mammals, including about a billion people worldwide. Trichuris eggs are usually acquired accidentally and if hatching is successful the emerging larvae burrow into the intestinal wall. The young worms eventually migrate downwards and taking up permanent residence in the cecum or colon where they mate and begin releasing eggs into the environment.
This is an excellent strategy for the worms because their dispersal into new hosts depends on a life in the nether regions of the intestines where they can easily discharge their eggs along with the host’s feces. Notably, whipworms are amazing egg producers; during the year or so that she lives, each adult female produces between 5,000 and 20,000 eggs a day.
Bacterially-Driven Hatching Mechanisms Revealed
Investigating whipworm reproduction strategies using the common mouse parasite Trichuris muris, microbiologists Richard K. Grencis PhD, Ian S. Roberts PhD and their colleagues at the University of Manchester in the U.K. discovered that bacteria clustering around the larva-emerging portals at the eggs’ poles were extending arm-like projections called fimbriae and attaching them to pole receptors.
In their initial experiment, the researchers examined the relationship between whipworm eggs and bacteria in microbial-rich explants of mouse cecum. They noted that optimal hatching occurred when T. muris eggs were incubated in close contact with the bacteria for at least 30 minutes at 37 degrees C; colonization and temperature clues that make sure the parasite is hatching in the right place, the large intestine – not the small intestine or stomach.
Then they confirmed the direct role of bacteria in the egg-hatching process by incubating T. muris eggs in pure cultures of Escherichia coli and showed that these quintessential lab bacteria alone induce hatching as efficiently as the more natural array of flora in the gut explants. When bacterial parts were filtered out of the culture the eggs remained dormant, convincing the scientists that a structural component of the bacterium, not a secreted chemical was the hatch trigger. They also boiled the E. coli and zapped them with a bacteriostatic antibiotic and proved to their satisfaction that “It didn’t seem to matter if the bacteria were viable or not, just that they were intact.”
Finally, the University of Manchester microbiologists tested a variety of other microorganisms and, in addition to showing that egg-hatching ability is a widely-held talent, they identified a type 1 fimbriae as a hatching mediator; but not the only one because “neither Pseudomonas aeruginosa nor Staphylococcus aureus have these particular fimbriae but still induce whipworm larvae out of their eggs,” says Dr. Grencis.
Hosts Benefit from Macrofauna as Well as Microflora
No one as yet knows exactly what the bacteria get in return for helping the worms hatch, but the relationship does offer some definite advantages to the hosts. Controlled damage of the intestine by infecting nematodes, for example, increases the contact between gut microbes and immune cells which may help generate T-cell responses to alien bacterial pathogens.
And while the researchers do not encourage people to deliberately infect themselves with parasitic worms (that’s far too hazardous), Grencis notes that having a low number of worms, not enough to do any harm, may be an effective way to develop a robust immune response.
Moreover, exposure to microbes during childhood helps the immune system develop tolerance to normal environmental antigens, and co-evolved macrofauna such as gut-dwelling nematode parasites are an important part of the process. “There are more parasitic worm infections in the developing world but fewer autoimmune and allergic problems,” adds Grencis.
"Eventually," says Duke University scientist William Parker PhD, "Physicians may be colonizing people at risk for immune-related disorders such as inflammatory bowel disease, eczema, and even asthma with helminths, thereby putting back some of the larger gut creatures that our overly hygienic Western society has removed."
Reserch details and other information can be found in:
Hayes KS, Bancroft AJ, Goldrick M, Portsmouth C, Roberts IS, Grencis RK: Exploitation of the Intestinal Microflora by the Parasitic Nematode Trichuris muris. Science; 11 June 2010; 328, pp.1391-1394.
Rook, GAW. Review series on helminths, immune modulators and the hygiene hypothesis: The broader implications of the hygiene hypothesis: Immunology: 2008; 126, pp. 3-11.
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