The mosquito population in Pennsylvania may be up this year, but cases of West Nile virus are currently down.

West Nile virus is a disease that infects birds and mosquitoes and transmitted to humans through infected mosquito bites. It can cause encephalitis, an inflammation of the brain; or meningitis, inflammation of the lining of the brain and spinal cord.

It was first detected in the United States in 1999, when 62 people in New York became ill and seven died; and has since spread into other states.

According to Amanda Witman, a spokeswoman for the Pennsylvania Department of Environmental Protection, the lower number of West Nile virus-positive mosquitoes can be attributed to their delayed emergence as a result of the colder-than-normal spring.

She noted that through DEP's surveillance and control program, which runs from May to October, they are collecting more mosquitoes in their traps this year than last year, but the virus just isn't present in most of the current mosquito population.

As of July 23, only 34 West Nile virus-positive mosquitoes have been found in the state.

Last year, which was a record year for West Nile virus, DEP found 3,410 positive mosquitoes. In addition, there were also 135 West Nile virus-positive birds discovered; and 60 human cases reported.

The low numbers may change though as the summer continues.

Witman explained that the weather the state experienced over the last few weeks, with excessive heat and heavy rains, are "ideal for breeding."

"West Nile virus itself thrives on a hot environment, and typically gains strength in hot conditions," she said. "As far as what we can expect for the rest of the summer, it's really hard to say. Mosquito breeding and the spread of West Nile virus are controlled by many factors, all of which are unpredictable and out of our control.

"What I can say is that based on what we have seen so far, it is reasonable to conclude that this year will be far different from last year and we will not find as much of the virus in the state."

People can reduce the risk of West Nile virus in their surroundings by eliminating the places where mosquitoes breed, DEP reports.

Tips they provided include:

Ÿ Dispose of tin cans, plastic containers, ceramic pots, discarded tires, or any object on your property that could collect standing water.

Ÿ Drill holes in the bottom of recycling containers left outdoors.

Ÿ Clean roof gutters every year, particularly if leaves from nearby trees clog the drains.

Ÿ Turn over plastic wading pools and wheelbarrows when not in use.

Ÿ Don't let water stagnate in birdbaths.

Ÿ Aerate ornamental pools or stock them with fish.

Ÿ Clean and chlorinate swimming pools and remove standing water from pool covers.

Ÿ Use landscaping to eliminate standing water that collects on your property.

Ÿ Standing water that cannot be eliminated should be treated with BTI products, which are sold at outdoor supply, home improvement, and other stores. BTI is a naturally occurring bacterium that kills mosquito larvae but is safe for people, pets, aquatic life and plants.

Additionally, residents can prevent mosquito bites, by:

Ÿ Making sure screens fit tightly over doors and windows to keep mosquitoes out of homes.

Ÿ Wearing long-sleeved shirts, long pants and socks when outdoors, or in areas known for having large numbers of mosquitoes.

Ÿ Reducing outdoor exposure at dawn and dusk during peak mosquito periods.

Ÿ Using insect repellants according to the manufacturer's instructions. An effective repellant will contain DEET, picaridin or lemon eucalyptus oil.

For more information about West Nile virus, including current test results, visit www.westnile.state.pa.us.

For information on symptoms of West Nile Virus in humans, visit the Centers for Disease Control and Prevention website at www.cdc.gov/westnile/index.html.