FRIDAY, May 18 (HealthDay News) -- In a finding that could give insight into human sleep patterns, U.S. researchers say there's a two-way link between sleep and immune system function in fruit flies.

Researchers at Stanford University School of Medicine found that sick fruit flies can't sleep, and this lack of sleep makes them more susceptible to infection. The study was published in the May 15 issue of Current Biology.

"When flies get sick, they stop sleeping. Disrupting sleep in turn disrupts the immune system, which makes them even more infected, and it's downhill from there in a 'spiral of death,'" senior author David Schneider, an assistant professor of microbiology and immunology, said in a prepared statement.

The flies in this study were infected with one of two kinds of bacteria -- Streptococcus pneumoniae or Listeria monocytogenes. The infected flies suffered a disruption of their circadian rhythm, which controls day and night patterns of activity. Infected flies had fewer sessions of sleep and shorter periods of continuous sleep than uninfected flies.

It's not clear whether the sick flies' impaired sleep behavior was caused by a disruption of the central clock in their brain, an area that exhibits circadian gene activity, the researchers said. But they noted that the sick flies' behavior was similar to that of flies with disruptions in the genes that control circadian rhythm.

The study authors said they hoped their research would prompt scientists who study vertebrate species to look more closely at the molecular factors that may influence sleep and immunity.

Schneider noted that fruit flies and vertebrates share may of the same circadian clock genes.

"As usual, it doesn't work in exactly the same way, but what the fly does is let us find genes that are involved in the process, and then go figure out exactly how they are rewired to work in the human. The fly is really good for prospecting," he said.