WASHINGTON — By figuring out what caused mosquito larvae living in polluted Florida water to become ill, government scientists have isolated a virus lethal to the insects that spread West Nile fever.
The U.S. Department of Agriculture recently received a patent on a way to use the virus as a mosquito control pesticide and is looking for a private partner to bring the new technology to market. An official said it likely will be at least two years before any commercial use is possible.
It took about that long for entomologists at the agency's Agriculture Research Service laboratory in Gainesville, Fla., to isolate the mosquito disease-causing virus.
"We do it the old-fashioned way. We go out in the field and collect mosquitoes," said James J. Becnel, the insect pathologist who found the virus.
Becnel said he collected larvae from Culex mosquitoes, the insects believed most responsible for spreading West Nile virus, brought them back to his laboratory, and examined any sick ones.
"We look for everything: virus, bacteria, fungus, protozoa, anything that makes them sick," he said.
After concluding that larvae collected from a pond polluted with pig farm runoff were infected with a type of virus known as baculovirus, Becnel and other scientists at the laboratory set out to infect others.
After months of experiments, they learned that mosquitoes fell ill with the virus only when the water contained magnesium.
"Once we found that by simply adding magnesium, we could get 100 percent infection, that was the breakthrough," said Becnel. "All we do now is go to Wal-Mart and buy some Epsom salts (magnesium sulfate), add it to the water along with the virus and we get infection."
In two or three days, up to 95 percent of the larvae die. The baculovirus infects only Culex mosquitoes, not other insects, plants, wildlife or people, he said.
Other biological controls for the so-called West Nile mosquitoes do not work well in polluted water, Becnel said, but the baculovirus works fine. When a sick mosquito dies of its infection, it releases billions of new virus particles into the surrounding water, and this second-generation virus infects other mosquitoes.
The Centers for Disease Control and Prevention said 4,156 cases of West Nile virus were reported in the United States last year, and 284 deaths.
Long common in Africa, southern Europe and the Middle East, West Nile virus was not found in the Western Hemisphere until 1999, when it appeared in the New York City area. It has since spread to most of the country, as well as Canada, Mexico and the Caribbean.
CDC recommends "personal protective measures" to reduce contact with mosquitoes. These include reducing time outdoors, particularly in the early evening hours, wearing long pants and long-sleeved shirts, and applying mosquito repellent to exposed skin.
The USDA is looking for a private partner to license the baculovirus-magnesium system as a larvicide for controlling mosquitoes.
Donald Nordlund, a privatization expert with the USDA laboratory in Athens, Ga., said that even if a private partner licenses the system, it could take at last two years to get the larvicide approved by the Environmental Protection Agency and to begin commercial production.