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Viral encephalitis

Description

An in-depth report on the causes, diagnosis, treatment, and prevention of viral encephalitis.

Alternative Names

West Nile virus

Prevention

The risk for mosquito-born infections is highest between dusk and dawn, when mosquitoes feed. A good insect repellent is very helpful in reducing the risk for vector-borne disease. The most complete personal protection program for adults and most children is to apply the insect repellant DEET to the skin and also permethrin to clothing and other surfaces.

DEET and Other Skin Products for Repelling Insects

DEET. Most insect repellents contain the chemical DEET (N,N-diethyl-meta-toluamide), which remains the gold standard of currently available mosquito and tick repellents. DEET has been used for more than 40 years and is safe for most children when used as directed. Comparison studies suggest that DEET preparations are the most effective insect repellents now available.

Concentrations range from 4% to almost 100%. The concentration determines the duration of protection. Experts recommend that most adults and children over 12 years old use preparations containing a DEET concentration of 20 - 35% (such as Ultrathon), which provides complete protection for an average of 5 hours. (Higher DEET concentrations may be necessary for adults who are in high-risk regions for prolonged periods.)

DEET products should never be used on infants younger than 2 months. According to the Environmental Protection Agency (EPA), DEET products can safely be used on all children age 2 months and older. The EPA recommends that parents check insect repellant product labels for age restrictions. If there is no age restriction listed, the product is safe for any age. The American Academy of Pediatrics recommends that children use concentrations of 10% or less; 30% DEET is the maximum concentration that should be used for children. In deciding what concentration is most appropriate, parents should consider the amount of time that children will be spending outside, and the risk of mosquito bites and mosquito-borne disease.

When applying DEET, the following precautions should be taken:

• Do not use on the face and apply only enough to cover exposed skin on other areas.
• Do not over apply and do not use under clothing.
• Do not apply over any cuts, wounds, or irritated skin.
• Parents or an adult should apply repellent to a child and not let the child apply it him- or herself. They should first put DEET on their own hands and then apply it to the child. They should avoid putting DEET not only near the child's eyes and mouth, but also on the hands (since children frequently touch their faces).
• Wash any treated skin after going back inside.
• If using a spray, apply DEET outdoors -- never indoors. Spray repellents should not be applied inside or directly on anyone's face.

Other Insect Repellent Products. In 2005, the U.S. Centers for Disease Control (CDC) added two new mosquito repellents to its list of recommended products: Picaridin and oil of lemon eucalyptus.

Picaridin, also known as KBR 3023 or Bayrepel, is an ingredient that has been used for many years in repellents sold in Europe, Latin America, and Asia. A product containing 7% picaridin is now available in the United States. Picaridin can safely be applied to young children and is also safe for women who are pregnant or breastfeeding. According to the CDC, insect repellents containing DEET or picaridin work better than other products.

In scientific tests, oil of lemon eucalyptus, also known as PMD, worked as well as low concentrations of DEET. However, oil of lemon eucalyptus is not recommended for children under the age of 3 years.

Permethrin for Clothing and Surfaces

Permethrin is an insect repellent used as a spray for clothing and bed nets, which can repel insects for weeks when applied correctly. Electric vaporizing mats containing permethrin may be very helpful. A permethrin solution is also available for soaking items, but should never be applied to the skin. Side effects from direct exposure may include mild burning, stinging, itching, and rash, but in general, permethrin is very safe and its use may even reduce child mortality rates from malaria. People allergic to chrysanthemum flowers or who are allergic to head-lice scabicides should avoid using permethrin.

Controlling Mosquitos Around the House

Eliminate Sources of Standing Water. Currently, the only proven method for reducing mosquito populations is to eliminate sources of standing water.

• Look for any source of standing water, where mosquitoes can breed. For example, discard any rubbish with standing water, such as old tires, cans, and bottles. (Even bottle caps can breed mosquitoes. Turn over wading pools and wheelbarrows when not in use. Change bird bath water every 3 - 4 days. A product called Mosquito Dunk can be used to prevent breeding in standing water.
• Swimming pools and hot tubs should be clean and chlorinated or drained and covered if not in use.
• Clean vegetation and debris from the edges of ponds.
• Gutters should be kept unclogged.

Mosquito Traps. There are a number of mosquito traps that use various methods for repelling or attracting and trapping the insects. Effective traps are expensive, and they usually require electricity or propane, which adds to the cost. Mosquito trap machines should only be used outdoors. While many traps can draw in significant numbers of mosquitoes, they have limitations and should not be relied on for sole protection.

All baits should be designed to attract the female mosquito, which is the primary transmitter of the viruses. However, different baits may be more or less effective. Some may even attract one species and not others. For example, a comparative study of three traps that used similar attractants found that after 20 hours, the Magnet Liberty and Mosquito Trap MK01 attracted 75% of mosquitoes in a single area, while the Sonic Web had attracted only 25%. However, all three traps tended to attract twice as many Aedes mosquitoes (which carry La Cross and Eastern Equine encephalitis) as the Culex (which transmits West Nile and St. Louis Encephalitis).

Bug Zappers . Insect light traps (commonly called bug zappers), which attract and electrocute insects, may actually spread viruses and bacteria that are on the insects. They are also not very effective for killing female mosquitoes.

Encouraging Natural Defenders. Some attempts have been made to control mosquito populations with natural defenders, including building bat and bird houses to attract natural predators or growing certain insect-repellent plants.

Citronella Candles . Burning citronella candles reduces the likelihood of bites. (Indeed, burning any candle helps to some extent, perhaps because the generation of carbon dioxide diverts mosquitoes toward the flame.)

Other Preventive Measures

Your home environment, personal hygiene, and what you wear can also help reduce your risk for mosquito bites.

• Wear trousers and long-sleeved shirts, particularly at dusk. One survey suggested that this measure may significantly reduce the incidence of mosquito-born disease.
• Sleep only in screened areas.
• Air-conditioning may reduce mosquito infiltration. Where air-conditioning is not available, fans may be helpful. Mosquitoes appear to be reluctant to fly in windy air.
• Don't wear perfumes.
• Cover up bare skin after dusk.
• Wash your hair at least twice a week.

Public Spraying

Public health measures are the best methods for controlling mosquitoes.

Spraying. Local areas that experience outbreaks of encephalitis from mosquitoes usually have a spraying program.

• Insecticides containing synthetic pyrethroids (permethrin, resmethrin, and sumithrin) are generally recommended by consumer groups as being the most effective and the least toxic to people (although they are toxic to fish and bees).
• Malathion and naral--another pesticide--are organophosphates and approved for spraying mosquitoes. Malathion specifically has been widely used in a number of areas. Organophosphates, however, can have toxic effects on the nervous system. Some people, for example, have reported being sick after exposure to Malathion. In addition, there is a risk that mosquitoes will develop resistance to it.

Report Dead Birds. Dead birds may be indicators that the West Nile has reached a specific region. People who spot any should report them to local public health authorities. You should never handle a dead bird with bare hands.

• Review Date: 1/18/2007
• Reviewed By: Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital

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