Reduce West Nile Virus Threat with Mosquito Control

UNIVERSITY PARK – Although West Nile virus made headlines in mid-June by showing up in mosquito samples taken in Blair County — the earliest it has shown up Pennsylvania in any of the last five summers – the disease has not been nearly as bad here as health officials feared, according to an entomologist in Penn State’s College of Agricultural Sciences.

West Nile virus, which can cause a potentially fatal form of encephalitis, is an invasive species that found its way to North America from Africa. The disease, which first showed up in the United States in 1999 in New York, is carried by birds and spread by mosquitoes. It now has been found in nearly every county in Pennsylvania.

The 2002 West Nile virus outbreak in North America was the largest encephalitic disease epidemic ever documented in the Western Hemisphere, and it was the largest West Nile virus outbreak ever documented, according to the U.S. Centers for Disease Control. But outbreaks since have not been so severe.

“Although scientists have been surprised at how rapidly it has disbursed here, the outbreaks have not been nearly as disastrous as some predicted,” said extension entomologist Steve Jacobs. “In Pennsylvania, the first cases of West Nile encephalitis were detected in 2001 (there were three cases). In 2003 the number of new human cases had risen to 237, but by 2006 the numbers had dropped to just nine human cases.”

It’s a good thing that the disease has not been worse in the United States because there isn’t much that can be done to isolate it, Jacobs lamented. “There is very little we can do to stop something like this,” he said. “All we can do, once the virus is spread throughout the state or the country, is to educate the public to wear insect repellents and recognize the disease so they can seek treatment. But in terms of general health risks to the public, West Nile is well down the list. I think many people believe the risks of dying from West Nile are much higher than they are.”

Ordinarily, mosquitoes are little more than a mild irritant, Jacobs said. But because they can transmit diseases to humans and pets — such as West Nile encephalitis, eastern equine encephalitis and canine heartworm — people should take steps to avoid being bitten and to eliminate mosquito-breeding areas.

Mosquitoes breed in standing water. Only female mosquitoes bite, according to Jacobs. “In most cases, the female must have a blood meal before laying eggs,” he said. “The females’ persistent search for blood brings them into houses and yards, where they may become annoying pests.”

Many mosquito problems can be traced to containers of water around the yard, such as children’s toys, pots and cans, tire swings, animal tracks and clogged rain gutters. Neighborhood breeding areas can include construction sites, trash dumps and cemetery urns or planters. Most mosquitoes remain within a half-mile of where they hatch, but some can fly miles.

During warm weather, mosquitoes can breed in any puddle that stands for more than four days. “The most effective way to control mosquitoes is to eliminate standing water,” said Jacobs. He advises homeowners to:

— Remove old tires, tin cans, buckets, glass jars, toys and other water-catching objects.

— Tightly cover rain barrels to prevent egg-laying.

— Change water in bird baths by flushing with a hose at least once a week.

— Fill tree holes with sand or cement or drill holes to allow drainage.

— Keep rain gutters clean and free of obstructions.

— Drain excess water from flower pots.

— Keep swimming pools covered when not in use.

— Turn over wading pools and wheelbarrows when not in use.

— Empty accumulated water from boats and cargo trailers.

— Clear aquatic vegetation from around the edges of ponds to allow fish to feed on mosquito larvae and pupae.

When going outdoors for an extended period of time, insect repellents can provide protection from mosquito bites. “Repellents can protect for up to five hours,” said Jacobs. “But because people vary in their attractiveness to mosquitoes, the effectiveness of the repellent may depend on the individual.”

Before using a repellent or insecticide, be sure to thoroughly read and understand all directions and cautions on the product label, Jacobs warned.

For a free fact sheet on mosquitoes, contact the nearest county office of Penn State Cooperative Extension or visit online.

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