The Medical Minute: Bugged by mosquitoes?

By Dr. John Messmer
Penn State Milton S. Hershey Medical Center

What's that buzzing noise? Believe it or not, mosquito season is already here again. Why do we even need mosquitoes? What purpose do these pesky insects serve? In the grand scheme of biology, mosquitoes are an important food source for other insects and birds, and fish eat their larvae. Of course, these pests also are a nuisance and can carry disease, so some caution is necessary when we spend time outside.

West Nile virus may be the most high profile disease carried by some mosquitoes. For the last few years this viral infection has made headlines because of the increasing number of cases. In Pennsylvania, the number of diagnosed cases increased from 62 in 2002 to 247 in 2003. Eight people in Pennsylvania died of West Nile encephalitis in 2003. The elderly and those with chronic illnesses are most at risk for death, nonetheless, caution is reasonable.

A significant first step to protect yourself and your family 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 your neighbors to do the same.

Sometimes water can not be emptied frequently or at all. In these cases, there is a kind of biological warfare available to deal with the mosquito. BTI or Bacillus thuringiensis israeliensis 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 our 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 with DEET (N, N-diethylmetatoluamide) are very effective at keeping these pests away. While DEET doesn't actually repel mosquitoes it does "mask" us so mosquitoes can't find us. 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 sparingly applied -- no need to be generous as you would with sunblock. Put a little on your hands, rub them together and then rub your hands over your exposed skin or that of your child. DEET should be reapplied 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. Vitamins and Avon Skin-so-soft™ do not work reliably as mosquito repellants.

What if you are bitten? Don't panic! West Nile virus is still uncommon. Cold compresses and hydrocortisone cream can help with the itching.

For more information on mosquitoes and West Nile virus, visit http://www.hmc.psu.edu/healthinfo/uz/westnile.htm