Parasite brood gets help from nearby microbes

The question of which came first, the whipworm or the whipworm egg, leaves out a key player: bacteria.

Eggs of the parasitic whipworm, whose potential hosts include humans, won’t hatch in their host’s intestine until they get the go-ahead from nearby gut bacteria, researchers report June 10 in Science.

The work reveals how the parasite avoids hatching in the wrong place. It also highlights that parasite-host interactions don’t occur in isolation.

“This is a very nice illustration of the interdependence of things,” says Rick Maizels, an immunologist at the University of Edinburgh in Scotland who was not involved in the work. The finding also suggests a means of stymieing whipworm infection, Maizels says, as interrupting the bacterial message could prevent whipworm eggs from hatching.

Nearly a billion people are infected by the whipworm species that affects humans. The small eggs can be eaten accidentally with rice or other grains. Once inside, the eggs hatch and the larvae burrow into the intestinal wall. Infection can lead to anemia, diarrhea and other problems.

In the new work, co-author Ian S. Roberts of the University of Manchester in England and his colleagues investigated a mouse-infecting whipworm, one of about 50 species of the intestinal parasite Trichuris. In small sections of mouse intestine, the researchers found, many more of the whipworm’s eggs hatched in the presence of live E. coli than of E. coli that had been killed by boiling. Several other kinds of bacteria, including a staph species, also induced hatching.

The team noticed that the bacteria seemed to cluster at the ends of the whipworm eggs, as if they were physically contacting the egg rather than communicating via a chemical messenger. Sure enough, experiments revealed that the thin, rodlike projections that protrude from the bacteria were binding to proteins on the surface of the whipworm eggs. And giving live mice antibiotics to kill their gut bacteria also reduced their worm load.

Hatching was also influenced by temperature — eggs hatched only at about 37 degrees Celsius. This suggests the whipworms have double insurance that they are indeed inside a host, the researchers say. Taken together, the right temperature and the gut bacteria directive seem to tell the eggs that they are inside a host and can get hatching.

Many scientists are now studying gut microflora, but the new research is a reminder to not forget about interactions with the bigger fauna such as parasitic worms, Roberts says. And the low-level infection that comes from the interplay between bacteria and whipworm may help the body develop a robust immune response that somehow prevents more severe infections. “Having a few worms knocking around might not be a bad thing,” he says.