The Medical Minute: Mosquito season -- ready or not, here it comes

May 02, 2005

By John Messmer
Department of Family & Community Medicine
Penn State Milton S. Hershey Medical Center
Penn State College of Medicine

Believe it or not, mosquito season is here again. Mosquitoes are an important food source for other insects and birds, plus fish eat their larvae. Unfortunately, these pests also are a nuisance that can carry disease, so some caution is necessary when spending time outside.

In the United States, West Nile virus may be the highest profile mosquito-borne disease. For the last few years this viral infection has made headlines because of the increasing number of cases. It may be that West Nile virus cases are not increasing as rapidly as in the first two years. While this is good news, it is not cause for complacency.

A significant first step in protection is to remove breeding grounds for mosquitoes. All species of mosquito require standing water to breed. Around the home there are many sources of standing water. Clean out bird baths regularly; empty wading pools daily; eliminate old tires or put holes into tires and other objects, such as buckets, flower pots and recycling bins to allow water to drain; and clean rain gutters. Ask neighbors to do the same.

Sometimes water cannot be emptied frequently or at all. In these cases, there is a kind of biological warfare available to deal with the mosquito. Bacillus thuringiensis israeliensis (BTI) is a common, soil-based bacterium that destroys the larvae of mosquitoes and black flies. Sold in cakes by hardware and gardening supply stores, it can be placed into containers that cannot be emptied, such as ponds. It is harmless to humans, animals, fish and birds and is environmentally safe.

Prevention of breeding near homes helps, but mosquitoes can fly a mile or more, so when outside for long periods, particularly in morning and early evening when mosquitoes are most active, wear long sleeves, socks and long pants. Use mosquito netting when camping. Insect repellants are a must for outdoor activity. Mosquito season also is sunburn season. Apply sunscreen first, then after it has dried, apply insect repellant.

Insect repellants with DEET (N, N-diethylmetatoluamide) are very effective at keeping these pests away. While DEET doesn't actually repel mosquitoes, it does mask people so mosquitoes can't find them. Higher concentrations don't work better, they just last longer. Children should use concentrations of 10 percent or less. Adults can tolerate concentrations up to 30 percent. DEET should be applied sparingly; no need to be generous as with sunblock. To apply, people should put a little on their hands, rub them together and then rub their hands over exposed skin. DEET should be re-applied every few hours, particularly if sweating. Although DEET is oily, consider rubbing it sparingly over lighter clothing to reduce the likelihood of bites through the clothes. Some people advocate using B vitamins and Avon Skin-So-Soft, but these do not work as reliably as mosquito repellants.

This year, the Centers for Disease Control (CDC) has included new products in its list of effective insect repellants. One new insect repellant is picaridin, which has been used in Australia and Europe and is accepted by the World Health Organization for repelling mosquitoes that carry malaria. It is essentially odorless, non-oily and may be better-tolerated on the skin. It is not a petroleum product so it will not harm plastics. DEET should be washed off when outdoor activity is over, but picaridin does not have that recommendation. It has been tested to be as effective as DEET and may be less toxic.

Oil of lemon eucalyptus is another product that will be on shelves soon. Studies show it to be about as effective as DEET and picaridin.

There is no need to panic if bitten. People older than 50 are at higher risk for serious reactions, but West Nile virus still is quite uncommon. Even those who contract it likely will do well if they are otherwise in good health. Treat the bite with cold compresses and hydrocortisone cream to help with the itching. If high fever, headaches, confusion and other severe symptoms develop, contact a doctor or emergency department.

For more information on mosquitoes and West Nile virus, visit online.

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Last Updated March 19, 2009