The mosquito population is as strong as it was at this point last year, but cases of the West Nile Virus are down, according to data collected by the Department of Environmental Protection.
"The mosquito population, in and of itself, is very strong," DEP spokeswoman Amanda Whitman said. "In some areas, it's even stronger than the population we saw last year."
The Pennsylvania West Nile Vile Control Program conducts a statewide survey for the virus each year. Only two mosquito testing samples have tested positive for the virus, occurring in Adams and Erie counties. No humans have contracted the disease.
There were 60 human cases of the virus in 2012, including seven in Delaware County. However, Whitman said 2013 is becoming one of the least prevalent years for West Nile.
A relatively warm winter followed by a warm and wet spring enabled surviving mosquitoes to come out much earlier in 2012, Whitman said. The mosquitoes fed on young birds that hadn't developed a resistance to the virus.
"It really amplified the virus to a degree that we have never seen before," Whitman said. "This year, having a pretty cold spring and not as warm of a winter, the amplification process for the mosquito population was much less than what we saw last year."
There are more mosquitoes flying around this summer, Whitman said, but not by a huge amount. They particularly are higher in areas that experienced significant flooding, like Clearfield and Crawford counties.
Those counties have witnessed increased populations of flood water mosquitoes, a breed whose eggs can lay dormant for 10 years, waiting for flood waters to rush over them and activate their hatching, Whitman said. York County has battled a heavy amount of Asian tiger mosquitoes.
Neither flood water nor Asian tiger mosquitoes carry West Nile Virus, Whitman said. Typical household mosquitoes are responsible for spreading the virus.
Whitman said Southeastern Pennsylvania was among the areas most affected by mosquitoes last year, largely because urban areas contain numerous instances of standing water.
Mosquitoes can breed in as little as a teaspoon of water, she said.
"Any standing water is bad standing water," Whitman said.