Health officials say it's too early to determine how widespread West Nile virus will be this summer, but advised people to take precautions now.
"It's almost impossible to predict, but we know it's out there everywhere," state Department of Health spokesman Richard McGarvey said of the virus, which was found in every county in the state last year. 
Mosquitoes begin breeding as soon as temperatures heat up, and a wet Pennsylvania spring is prime breeding season for the pests that carry West Nile virus.
Homeowners can reduce their risk of contracting the virus by limiting the amount of standing water around their property. Mosquito eggs are deposited in stagnant water, where the larvae grows.
Swimming pool covers, wading pools, tires, flower pots, garbage cans, rain gutters and long-standing puddles can contain enough water to breed mosquitoes.
"A mosquito can breed in as little water as a bottle cap," said Allegheny County Health Department spokesman Guillermo Cole.
Cole said the first known person in Allegheny County to contract the virus last year surfaced in June.
There were a total of 10 county residents to contract the virus last year, which was less than half the number of victims from the previous year.
"We think one of the reasons the virus wasn't as prevalent last year was because we started treating catch basins with pesticide," Cole said.
Cole said about 60,000 water retention basins were treated countywide in 2003, which almost immediately helped to reduce the mosquito population.
The state Department of Environmental Protection has proposed granting $6.4 million to counties for West Nile virus surveillance and treatment. All four of the Valley's counties are included in the grants, ranging from about $75,000 for Armstrong and Butler counties, to $144,000 for Westmoreland and $206,000 for Allegheny.
Vince Cappo, the virus coordinator in Armstrong County, said the county has contracted an outside pest control company to survey mosquito populations and use larvicide when necessary.
The state recommends using Bti, a naturally occurring bacteria that is poisonous when ingested by mosquito larvae but is not toxic to humans, plants, animals or other insects. The bacteria also is available for home use.
Aside from limiting mosquito breeding areas around the home, McGarvey said people should use insect repellant and avoid going outside at dawn and dusk to prevent mosquito bites.
West Nile virus can cause flu-like symptoms in humans and, in rare cases, can lead to a sometimes fatal swelling of the brain known as West Nile encephalitis.
Eight Pennsylvanians died after contracting the virus last year, although none of the victims lived in the Valley. Butler and Westmoreland counties each had four people who contracted the virus and three people from Armstrong County fell ill.
McGarvey said cats and dogs also contract the virus, though they rarely are seriously affected. However, about one-third of West Nile virus cases in horses are fatal.
"It runs the gamut in humans and animals," McGarvey said. "It's almost always fatal in birds like crows, hawks and blue jays, but it doesn't bother chickens in the slightest.
"For every 250 people who get infected, only about one will have a serious reaction," he said.