Mosquito-killing virus may slow down West Nile: researchers

By EMILY GERSEMA

See Canoe News Science April 23, 2003 for the picture and full story:

A larval Culex nigripalpus mosquito infected with the baculovirus CuniNPV. The arrows indicate the "white" regions of the mosquito midgut infected with the virus. These are the nuclei of midgut cells filled with virus particles. (AP /Agriculture Department)

WASHINGTON (CP) - A disease that kills mosquitoes could be one way to slow the spread of West Nile virus, the U.S. Agriculture Department says.

Jim Becnel, a scientist with the department's Agricultural Research Service, said Wednesday that he and a team of researchers have come up with a new method to kill mosquitoes by infecting them with an illness called baculovirus. It works only on mosquitoes. "It's kind of a killer for a killer," Becnel said.

The department wants companies to make mosquito-killing sprays from baculovirus and put them on the market. They believe it could kill mosquitoes potentially carrying West Nile virus, an illness that killed 284 people and sickened 4,156 in the United States last year.

In Canada, West Nile has afflicted residents of Nova Scotia, Quebec, Ontario, Manitoba and Saskatchewan. In Ontario, three deaths have been confirmed and more than a dozen others linked to the virus. Of 16 cases confirmed in Quebec, there have been two deaths.

The U.S. agency got a patent on baculovirus in February, but it's up to manufacturers to make commercial sprays because federal law prohibits the government from doing so.

Becnel said scientists discovered the mosquito-killing baculovirus in 1997 but took years to understand how it is transmitted. They've found it infects a particular species of mosquito, Culex, a major carrier of West Nile virus.

Researchers noticed it works especially well on young Culex mosquitoes living in polluted wet areas, such as water tainted with farm runoff or chemicals. To kill mosquito larvae, they add magnesium to baculovirus and spray it on the larvae. The insects are dead within two or three days.

Without magnesium, the infection won't spread, said Becnel, who works at the department's lab in Gainesville, Fla.

"Mosquitoes have protective barriers in their gut, so we're thinking that the magnesium helps the virus cross those barriers," he said.

It is just one method of limiting the growth of mosquitoes. Becnel noted that researchers have developed a product made from a bacterium, called BTI, to kill them, but he said it doesn't always work well in wet, polluted areas.

Pesticides are another way to kill mosquitoes, but they also kill other insects.

Becnel said researchers are continuing to study the genes that make up baculovirus so they can figure out precisely how it is transmitted to mosquito larvae.

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On the Net:

USDA Agricultural Research Service: ars.usda.gov