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Medically Speaking
West Nile Virus
By Margaret T. Hessen, MDThe recent rains have brought floods to some areas of the Delaware Valley, and a bumper crop of mosquitoes, as well. While the discomfort of mosquito bites certainly detracts from the pleasures of summer, it is important to remember that these pests can be hazardous as well as annoying. In Pennsylvania, mosquitoes carry and transmit West Nile Virus and other less common forms of viral encephalitis.
While the odds of acquiring these diseases are small, they are nevertheless real: I cared for two patients with proven West Nile disease here in Delaware County two summers ago. Most often, West Nile disease is mild or even asymptomatic, but it can have severe consequences, including death. It is important that we recognize mosquitoes for their potential to cause disease, and act accordingly.
The Pennsylvania Department of Environmental Protection is applying insecticide at various locations in Delaware County. There are a number of precautions that individuals can take to reduce the mosquito population and to minimize the chances of being bitten.
Since mosquitoes breed in stagnant water, get rid of any standing water that you can. Empty trash cans, buckets, flower pots, wheelbarrows, birdbaths, and other containers that have collected water during rainfalls. Cover or empty kids’ wading pools when they’re not in use. Empty or remove old tires, which are a common site for mosquito breeding and are often overlooked as a site of “standing water.”
Some naturally occurring areas of standing water in low-lying ground can’t be eliminated easily. Various insecticides are available to treat these areas. Chemical insecticides that are approved by the Environmental Protection Agency and are commercially available include organophosphate compounds and pyrethrins. Non-chemical alternatives include various naturally occurring harmless bacteria (Bacillus thuringiensis israeliensis—“bti”—or Bacillus sphaericus). Bti has been licensed for use in the US since the early 1980s, and is safe for humans and pets.
Another naturally occurring compound is methoprene. Though they are safe and effective, the Bacillus products and methprene kill only during the larval phase of mosquito development, and have little effect on adult mosquitoes. The chemical compounds mentioned above are effective in killing adult mosquitoes. Comprehensive information about chemical and non-chemical insecticides is available at www.cdc.gov/ncidod/dvbid/westnile/resources/wnvguidelines2001.pdf.
Personal protection against mosquito bites involves common sense measures and the appropriate use of mosquito repellant. Make sure window screens fit properly and are in good repair. Remember that mosquitoes are most active from dusk to dawn, and take particular precautions during those hours. Consider wearing long sleeves and long pants. Mosquito repellants containing permethrins or DEET are most effective.
Note that high concentrations of DEET may have side effects in young children, and even low concentrations should not be applied to young infants. In general, a concentration of 25-35% is safe and effective for all but the very young. Repellant of that concentration should be applied every 6 hours for best protection. Permethrin compounds can also be used to treat clothing (by spray or laundry additive), providing an additional (and longer lasting) safeguard.
Further information is available at the website above, at www.westnile.state.pa.us, and at the EPA website.
-end-Note: this article is presented through the efforts of the Delaware County Medical Society and is intended for informational purposes only, the contents should not be intended as medical advice. “You and Your Doctor – Preserve the Relationship”.
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