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Mosquitoes and the Diseases They Can Carry

Almost everyone has had the unpleasant experience of being bitten by a mosquito. Mosquito bites can cause severe skin irritation through an allergic reaction to the mosquito's saliva - this is what causes the red bump and itching. But a more serious consequence of some mosquito bites may be transmission of certain serious diseases such as malaria, dengue fever and several forms of encephalitis. Not only can mosquitoes carry diseases which afflict humans, but they also can transmit several diseases and parasites that dogs and horses are very susceptible to. These include dog heart worms and eastern equine encephalitis.

There are about 200 different species of mosquitoes in the United States, all of which live in specific habitats, exhibit unique behaviors and bite different types of animals. Despite these differences, all mosquitoes share some common traits, such as a four-stage life cycle. After the female mosquito obtains a blood meal (male mosquitoes do not bite), she lays her eggs directly on the surface of stagnant water, in a depression, or on the edge of a container where rainwater may collect and flood the eggs. The eggs hatch and a mosquito larva or "wriggler" emerges. The larva lives in the water, feeds and develops into the third stage of the life cycle called a pupa or "tumbler". The pupa also lives in the water, but no longer feeds. Finally, the mosquito emerges from the pupal case and the water as a fully developed adult, ready to bite.

Mosquito Life Cycle

The type of standing water in which the mosquito chooses to lay her eggs depends upon the species. The presence of beneficial predators such as fish and dragonfly nymphs in permanent ponds, lakes and streams usually keep these bodies of water relatively free of mosquito larvae. However, portions of marshes, swamps, clogged ditches and temporary pools and puddles are all prolific mosquito breeding sites. Other sites in which some species lay their eggs include tree holes and containers such as old tires, buckets, toys, potted plant trays and saucers and plastic covers or tarpaulins. Some of the most annoying and potentially dangerous mosquito species, such as the Asian tiger mosquito, come from these sites.

What You Can Do to Help Fight Mosquitoes

* Empty standing water in old tires, cemetery urns, buckets, plastic covers, toys, or any other container where "wrigglers" and "tumblers" live.

* Empty and change the water in bird baths, fountains, wading pools, rain barrels, and potted plant trays at least once a week if not more often.

* Drain or fill temporary pools with dirt.

* Keep swimming pools treated and circulating and rain gutters unclogged.

* Use mosquito repellents when necessary and follow label directions and precautions closely.

* Use head nets, long sleeves and long pants if you venture into areas with high mosquito populations, such as salt marshes.

* If there is a mosquito-borne disease warning in effect, stay inside during the evening when mosquitoes are most active.

* Make sure window and door screens are "bug tight."

* Replace your outdoor lights with yellow "bug" lights.

* Contact your local mosquito control district or health department. Neighborhoods are occasionally sprayed to prevent disease and nuisance caused by large mosquito numbers. If you have any questions about mosquitoes and their control, call your local authorities.

Using Insect Repellents Safely

Mosquitoes, biting flies, and ticks can be annoying and sometimes pose a serious risk to public health. In certain areas of the U.S., mosquitoes can transmit diseases like equine and St. Louis encephalitis. Biting flies can inflict a painful bite that can persist for days, swell, and become infected. Ticks can transmit serious diseases like Lyme disease and Rocky Mountain spotted fever. When properly used, insect repellents can discourage biting insects from landing on treated skin or clothing.

Choosing Insect Repellents

Insect repellents are available in various forms and concentrations. Aerosol and pump-spray products are intended for skin applications as well as for treating clothing. Liquid, cream, lotion and stick products enable direct skin application. Products with a low concentration of active ingredient may be appropriate for situations where exposure to insects is minimal. Higher concentration of active ingredient may be useful in highly infested areas, or with insect species which are more difficult to repel. And where appropriate, consider nonchemical ways to deter biting insects—screens, netting, long sleeves, and slacks.

Using Insect Repellents Safely

EPA recommends the following precautions when using insect repellents:

* Repellents should be applied only to exposed skin and/or clothing (as directed on the product label). Do not use under clothing.

* Never use repellents over cuts, wounds, or irritated skin.

* Don't apply to eyes and mouth, and apply sparingly around ears. When using sprays do not spray directly onto face; spray on hands first and then apply to face.

* Do not allow children to handle this products, and do not apply to children's hands. When using on children, apply to your own hands and then put it on the child.

* Do not spray in enclosed areas. Avoid breathing a repellent spray, and do not use it near food.

* Use just enough repellent to cover exposed skin and/or clothing. Heavy application and saturation is unnecessary for effectiveness; if biting insects do not respond to a thin film of repellent, apply a bit more.

* After returning indoors, wash treated skin with soap and water or bathe. This is particularly important when repellents are used repeatedly in a day or on consecutive days. Also, wash treated clothing before wearing it again. * If you suspect that you or your child are reacting to an insect repellent, discontinue use, wash treated skin and then call your local poison control center. If/when you go to a doctor, take the repellent with you.

* You and your doctor can get specific medical information about the active ingredients in repellents and other pesticides by calling the National Pesticide Telecommunications Network (NPTN) at 1-800-858-7378. NPTN operates from 6:30 a.m. to 4:30 p.m. (Pacific Time) 9:30 a.m. to 7:30 p.m. (Eastern Time) seven days a week.

Important Information on Using Pesticides

EPA recommends the following precautions when using an insect repellent or pesticide:

* Check the container to ensure that the product bears an EPA approved label and registration number. Never use a product that has not been approved for use by EPA!

* Read the entire label before using a pesticide. Even if you have used it before, read the label again—don't trust your memory.

* Follow use directions carefully, use only the amount directed, at the time and under the conditions specified, and for the purpose listed. For example, if you need a tick repellent, make sure that the product label lists this use. If ticks are not listed, the product may not be formulated for this use.

* Store pesticides away from children's reach, in a locked utility cabinet or garden shed.


United States Environmental Protection Agency, Office of Pesticide Programs.

Uploaded: 2/21/2004