FREDERICK, Md. (AP) -- In a sealed laboratory, scrub-suited Army scientists are probing the mysteries of mosquitoes that spread the West Nile virus, including one that could be especially adept at transmitting the sometimes deadly disease.
Controlling the U.S. outbreak of West Nile, which has killed seven people and sickened scores more since it first appeared in the country last year, depends partly on entomologist Michael Turell and his six-person team at the U.S. Army Medical Research Institute of Infectious Disease at Fort Detrick.
Their subjects include Aedes japonicus, an Asian mosquito species relatively new to this country. Although the main culprits so far have been common backyard mosquitoes in the Culex family, scientists say japonicus may be more capable of carrying the virus far from the New York City area, where all the U.S. deaths so far have happened.
"There is no question it is going to be a player," Turell said. "But is its role going to be the 10th most important mosquito or the second most important mosquito? That we don't know."
Where does it breed? When does it feed? What does it bite? Those are the questions the U.S. Centers for Disease Control and Prevention wants answered.
The agency asked the Army to join the West Nile fight shortly after the virus appeared for the first time in the Western Hemisphere last September, said Stephen Ostroff, West Nile coordinator at the CDC. Scientists at Fort Detrick develop defenses to germ warfare, but they also have battled outbreaks of Ebola and other exotic diseases around the world.
"The role that they are playing is a very important one," Ostroff said. The more the CDC knows about the mosquitoes that transmit the virus, the better it can advise the public on how to reduce the risk of infection, he said.
Scientists at Rutgers and Fordham universities also are studying links between West Nile and mosquitoes.
The researchers call the mosquitoes "vectors" -- organisms that transmit the virus by feeding on infected animals, especially crows, and then biting uninfected ones, such as humans. Some mosquito species are more competent vectors than others, and Turell has found that Aedes japonicus is among the best.
In laboratory tests, japonicus has been four to five times more effective than Culex pipiens in transmitting West Nile from infected chickens to virus-free chickens, he said.
Still, that doesn't necessarily mean japonicus is a competent vector in the wild. Scientists know it breeds in old tires, which puts it close to people, and that it feeds in the daytime. But they don't know if it feeds in the evening, when crows are roosting, or even if it feeds much on birds.
"The problem of trying to find a fed mosquito in the middle of a forest is extremely difficult," Turell said.
Nevertheless, researchers found the West Nile virus in a few swarms of japonicus mosquitoes in New York's Westchester County, where one of the West Nile deaths happened. The virus also has been found in at least five other mosquito species.
Researchers are intrigued by findings that japonicus and West Nile share much of the same U.S. territory. In the past two years, they have found the mosquitoes for the first time in most of the seven states -- Connecticut, Maryland, Massachusetts, New Hampshire, New Jersey, New York and Rhode Island -- where infected birds have been recovered.
"That's a pretty rapid spread for a mosquito in only two breeding seasons," Ostroff said. "If it continues to move at the pace it appears to have been moving, the potential to carry the virus farther afield is a cause for concern."
Scientists are less concerned, though, about japonicus' ability to transmit the virus to humans -- mainly because the evidence is scanty.
"This is the first time West Nile and japonicus have ever been in the same place at the same time," Turell said. He said the mosquito isn't found in Romania or southwestern Russia, the sites of other recent West Nile outbreaks. And in the Far East, where japonicus is common, West Nile fever is rare.
Ostroff said he was gratified that while the virus appears to be spreading among wild birds and insects, there has not been a rapid increase in human infections. Seven cases of human infection have been reported so far this year -- six in New York and one in New Jersey -- with no deaths.
"We have always acknowledged there isn't any way to prevent 100 percent of human illness, but what we could do is work to minimize the amount of human illness that we would see," Ostroff said. "I'd like to believe we're actually accomplishing some of that."