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Sleeping Sickness Parasites Are Social, Not Solitary

The parasites that cause deadly African sleeping sickness aren't as solitary as once believed, according to a new study. Instead, the single-celled creatures seem capable of communicating and even coordinating their behavior.

If organized armies of parasites seem scarier than loners, never fear: The findings have potential implications for fighting the deadly bugs, according to study researcher Kent Hill, an associate professor of microbiology, immunology and molecular genetics at the University of California, Los Angeles.

"A lot of new possibilities are opened up for interfering with the disease or the development of the bug," Hill told LiveScience.

Parasite party

Trypanosoma brucei, the protozoan parasite that causes African sleeping sickness, travels from human to human through the bite of the tsetse fly. The first symptoms of the disease are fever and aches, but once the parasite crosses into the brain, people show signs of confusion, sleep disturbance and lack of coordination. Untreated, the disease is fatal.

Until now, T. brucei has always been studied in liquid cultures in the lab, Hill said. In that environment, the parasites stick to themselves, maneuvering through the liquid with their whip-like flagella.

"But when you think about the parasite in its normal context, which is in a tsetse fly or human host, it's usually not swimming around in liquid," Hill said. "In fact, it's exposed to tissue surfaces."

So Hill and his colleagues cultured the parasite on a semi-solid surface in the lab and found that the parasites acted very differently than they did in liquid. They came together like bacteria in a colony, coordinating their movements with one another, the researchers reported today (Dec. 13) at the American Society for Cell Biology's annual meeting in Philadelphia.

"Rather than behaving as individual cells, they actually come together as little communities," Hill said.

Stopping sleeping sickness

This peek at the social life of T. brucei is new, but Hill and his colleagues suspect other parasites might behave the same way if given a chance in the lab. Bacteria were once considered loners, Hill pointed out, but research eventually revealed that almost all bacteria communicate with and respond to one another. The same may be true of parasites, he said.

The next step, Hill said, is to find out more about how and why the parasites "chat" with one another. As part of the experiment, Hill and his team discovered proteins on the parasites' flagella involved with communication. Mutants with absent or disrupted proteins stopped socializing or became hypersocial.

"It's almost like somebody isn't really listening to people around them, and they get closer to each other than they should," Hill said.

The researchers also hope to learn more about the parasite community's structures. The idea, Hill said, is to both learn about cell signaling and find a way to quash T. brucei's life cycle.

"The idea that the parasites are social is really brand new," Hill said. "And it does suggest novel means of intervening with the bugs."

You can follow LiveScience Senior Writer Stephanie Pappas on Twitter @sipappas.

Stephanie Pappas
Stephanie Pappas

Stephanie Pappas is a contributing writer for Live Science, covering topics ranging from geoscience to archaeology to the human brain and behavior. She was previously a senior writer for Live Science but is now a freelancer based in Denver, Colorado, and regularly contributes to Scientific American and The Monitor, the monthly magazine of the American Psychological Association. Stephanie received a bachelor's degree in psychology from the University of South Carolina and a graduate certificate in science communication from the University of California, Santa Cruz.