Marion officials are urging "caution, not panic" after a mosquito tested positive for West Nile virus earlier this month.

The state Department of Public Health notified the town on July 22 that the virus was found in a single mosquito specimen collected.

"There was one infected mosquito found," said Marion Board of Health member Kathy Downey, explaining that mosquito testings occur weekly throughout the state. "As the season progresses, there are more mosquitoes, and so more mosquitoes to test. A single positive identification is reason for caution, but it isn't the start of an epidemic."

West Nile is most commonly transmitted to humans by the bite of an infected mosquito. The mosquitoes that carry the virus are common throughout the state, and are found in both urban and rural areas. While West Nile can infect people of all ages, people over the age of 50 are at higher risk for a severe infection.

Mosquitoes prefer to lay eggs in damp ground or on water itself. With a higher-than-average rainfall of about 17" from April - June (the average rainfall over the three-month span is 12.5"), a larger crop of mosquitoes than usual seemed like a distinct possibility. And, with a larger number of mosquitoes than usual comes a larger chance of mosquito-borne viruses.

Downey explained that of all the people bitten by a mosquito with West Nile, only 20 percent show any symptoms at all -- 80 percent are asymptomatic and display no signs of illness.

Of the 20 percent who are affected, less than one percent develop the serious and neurological side effects that West Nile is known for. In that case, Downey said, hospital treatment should be sought.

"We take it very seriously," she said of the West Nile identification, "but people who exercise appropriate caution shouldn't have an issue."

The Massachusetts Department of Health offered several tips to help prevent mosquito bites:

The hours from dusk to dawn are peak biting times for many mosquitoes. Consider rescheduling outdoor activities that occur during evening or early morning.

Clothing can help reduce mosquito bites. Although it may be difficult to do when it’s hot, wearing long-sleeves, long pants and socks when outdoors will help keep mosquitoes away from your skin. Use mosquito netting on baby carriages and playpens outdoors.

Use an insect repellent with DEET, permethrin, picaridin, or oil of lemon eucalyptus oil.

There are also many solutions for mosquito-proofing your home:

Drain standing water. Many mosquitoes lay their eggs in standing water. Limit the number of places around your home for mosquitoes to breed by either draining or getting rid of items that hold water. Check rain gutters and drains. Empty any unused flowerpots and wading pools, and change water in birdbaths frequently.

Install or repair window screens. Some mosquitoes like to come indoors. Keep them outside by having tightly-fitting screens on all of your windows and doors.

The Marion Board of Health works closely with the Massachusetts Department of Public Health and other agencies. Contact the Marion Board of Health at 508-748-3530 with any questions.

Information about West Nile virus and reports of current and historical West Nile virus activity in Massachusetts can be found on the Massachsusetts Department of Public Health website at www.mass.gov/dph/mosquito.