17 December 2010
New research on the parasite that causes sleeping sickness suggests possible new ways to attack the disease.
African sleeping sickness affects mostly rural people in 36 sub-Saharan countries. The World Health Organization says there are currently an estimated 30,000 cases. Left untreated, it is fatal.
Sleeping sickness is caused by a parasite that is transmitted to humans by the tsetse fly. The parasite is a one-cell protozoa like ones you might have seen under a classroom microscope, floating around in fluid.
"But it turns out that, under the right conditions, they can actually transition to a multi-cellular form," says Kent Hill, a professor at the University of California, Los Angeles (UCLA) Department of Microbiology. "And in that form there's groups of cells that can sense their environment, that can communicate with one another, and that can engage in coordinate activities."
Hill and his colleagues used an artificial material in the lab to simulate a surface like the tissue inside an infected person. They found that the parasites gathered together in groups on these lab surfaces.
"And that is when we discovered that they change from acting as individual organisms, where they'd come together as these little groups, and then the little groups would actually send out parasites to look for more parasites and make the group bigger."
For years, microbiologists knew about this sort of grouping behavior in bacteria, but it had never been observed before in microbes like the sleeping sickness parasite.
"So we're really, really excited about it because it was kind of a really new observation," Hill says. "It was something we weren't expecting. And it turns out that once we discovered it, if we look at other microbes and bacteria, we kind of felt that we were a little surprised we didn't see it before."
According to Hill, the discovery of this previously-unknown aspect of the parasite's lifecycle opens up new possibilities for disrupting that lifecycle to stop the disease.
For example, when they are grouped together, the individual parasites communicate with each other by exchanging proteins, which bind to receptors on the surface of the cell.
"And so what we've got now are proteins on the parasite that are accessible on live cells to small molecules - meaning like drugs - that you could add to live cells, and they interfere with behavior of the parasite. And so we hope that this will lead to more ability to develop drugs for targets that are accessible on the parasites."
Although this work is still very much in the early research stage, Hill says it's possible that if drugs can be developed to target the sleeping sickness parasite, the same general principle might also be used against the parasites that carry some other tropical diseases including malaria and leishmaniasis.
Hill of the UCLA Department of Microbiology presented his research at the annual meeting of the American Society for Cell Biology in Philadelphia.