Common mosquitoes carrying the West Nile virus have been found in Allegheny County, the first of the season reported by health officials. But now, for the first time, the Asian tiger mosquito, an aggressive biting insect that is active in daylight hours, has been reported infesting an entire neighborhood in the county, according to the Allegheny County Health Department.

Several samples of the invasive species, Aedes albopictus, were collected Monday from an area in West Mifflin. It has been found in the county before but not in such concentration, health officials said.

Named for its Southeast Asia origin and characteristic black-and-white striped legs and body, the mosquito was first found in the southern United States in the mid-1980s. Since then, the health department reports, it has migrated throughout the Midwest and Northeast, including Philadelphia and York counties.

According to the Maryland Department of Agriculture website, the insect has been a major pest and public health threat since first found in the state in 1987, in a used tire processing plant in Baltimore. Health experts throughout the country say they believe the mosquito spread through the international trade in used tires. Tiger mosquitoes are closely associated with used tires, where they deposit eggs and larvae develop.

The Maryland site says, "It is likely that tires imported to Houston, Texas, from Japan in 1985 brought tiger mosquitoes to the United States." Afterward, the trade of used tires within the country aided the spread of the species, the site says.

From the Baltimore plant area, the mosquito spread to neighborhoods where outside containers holding water were common.

Allegheny County health officials warn that in addition to West Nile virus, the tiger mosquito can transmit other diseases to humans and domestic animals. In an announcement Wednesday, they said, "If no controls are applied, it may reproduce and spread to other areas of the county, but efforts are planned to control the source of the problem in West Mifflin."

West Nile was found in familiar mosquitoes collected last week from Pittsburgh's West End and North Side. The northern house mosquito, Culex pipiens, is the species thought to spread the most cases of the virus in Pennsylvania, according to Penn State entomologists.

As a precaution against bites, people are advised to limit the amount of time spent outdoors between dusk and dawn and to use insect repellent.

People are asked to help keep the mosquito population down by eliminating stagnant water. That includes getting rid of tires, buckets, flowerpots, junk piles and cans; cleaning out roof gutters and street drains; changing birdbath water frequently; emptying wading pools when not in use; filling in depressions where water accumulates and repairing leaky outdoor faucets.

West Nile virus causes serious symptoms in a few people, according to the Centers for Disease Control and Prevention. About one in 150 people infected with the virus can get high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis. Milder symptoms occur in up to 20 percent of people infected with the virus, and no symptoms show in about 80 percent of people infected.

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