New mosquito capable of carrying West Nile found in Missouri

The insects can transmit the virus to humans after feeding on infected birds.

ST. LOUIS -- A species of mosquito common in the eastern U.S. and capable of carrying the West Nile virus has made its way to the Midwest for the first time, a finding made by a college undergraduate, Washington University officials said Monday.

Stephanie Gallitano, a Washington University junior chemistry major from Chicago, was studying the egg-laying habits of mosquitoes native to Missouri this summer at the Tyson Research Center in Eureka, Mo. She took eggs to a lab and some developed into a type of insect she didn't recognize.

"Under the microscope, they looked completely different than anything I'd ever seen before," Gallitano said. "It had different proportions for its body. I looked through all of the books and could find nothing like it."

It turned out to be an invasive Asian mosquito known as Ochlerotatus japonicus, and marked the farthest west the species has been seen in the central United States, according to the Chevy Chase, Md.-based Howard Hughes Medical Institute. Gallitano's field work was part of an HHMI summer research project.

Jonathan Chase, associate professor of biology at Washington University, said the potential impact on humans is not yet known. He noted that the mosquito is a forest species "and we know little about its ecology or feeding preferences."

Wild populations have tested positive for West Nile, he said. "But has this mosquito ever transmitted it to a human? That we don't know."

West Nile virus spreads when mosquitoes feed on infected birds. The insects can then transmit the virus to humans.

In Illinois so far this year, 172 cases of West Nile disease have been reported, resulting in three deaths, according to the Illinois Department of Public Health. The fatalities were an 85-year-old Lake County man and two 92-year-old Cook County women.

This year's cases have almost more than doubled last year's total of 60, but health officials said increased spraying and monitoring have prevented a repeat of 2002, when Illinois led the nation in cases. That year, the virus infected 884 people in Illinois and killed 67.

Most people who are infected develop no symptoms or become only mildly ill. Symptoms include fever, headache, body aches, skin rash and swollen lymph nodes.

Chase cautioned the finding presented no reason to panic. Researchers say they will investigate the ecology of the Ochlerotatus japonicus and its interactions with other mosquitoes.

Gallitano's mentor and postdoctoral fellow James Vonesh said it is likely the new breed is not only in Missouri but in Illinois and other Midwestern and prairie states. Washington state has reported the Asian mosquito, but otherwise, none have been seen east of Michigan.

The species was first documented in New York state and New Jersey in 1998. By 2003, it had been reported in at least 19 other eastern states.

The findings will be reported in the December issue of Journal of Vector Ecology. The journal agreed to announce the finding early because September is the peak month for West Nile virus in the mosquito population.

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On the Net:

Howard Hughes Medical Institute: http://www.hhmi.org.

Washington University: www.wustl.edu.

Tyson Research Center: www.biology.wustl.edu/tyson