Encephalitis: Viral

Description

Prevention

The risk for mosquito-born infections is highest when mosquitoes feed, between dusk and dawn. A good insect repellent is helpful. It should be noted, however, that this precaution alone does not significantly reduce 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 permethrin to clothing and other surfaces.

Use of 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. Comparison studies suggest that DEET preparations are the most effective insect repellants now available. Concentrations range from 5% to almost 100%. DEET has been used for more than 40 years and is safe for even most children when used as directed.

Experts recommend that most adults and children over 12 years old use preparations containing a DEET concentration of 20% to 35% (e.g., Ultrathon), which provides complete protection for an average of five hours. (Higher DEET concentrations may be necessary for adults who are in high-risk regions for prolonged periods.) A concentration of 10% or less is recommended for children ages two to 12. In general, infants under 12 months should use non-DEET repellents, such as soybean-based Bite Blocker. Some experts believe low DEET concentrations are safe even in infants over two months old. Parents traveling to or living in high-risk areas should check with their physician.

It should be stressed that the effectiveness of DEET varies from individual to individual and depends on climate changes. For example, it can be washed off during swimming or by rain. Higher temperatures make it less effective. DEET, particularly in very high concentrations, can also dissolve plastics, including those used in glasses and watches and some synthetic clothing. DEET should not be put on clothing.

Overexposure to DEET at any age has produced toxic effects, including itching and rash and, in severe cases, irritability, insomnia, and confusion. It should be noted, however, that it has been intensively studied for 40 years and used in billions of applications. Only 50 such toxic reactions have been reported and most resolved without any consequences.

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 a 2002 comparison study, soy-based Bite Blocker was the only significant rival to DEET, with protection that averaged over an hour and a half. (This was slightly better than OFF! Skintastic for Kids, a 3.75% DEET product.)

The citronella- or mixed oil based products (e.g., Buzz Away, Avons Skin-so-Soft, Natrapel, Herbal Armor, Green Ban) only protected for an average of 20 minutes or less. (The lemon-citronella products offered the least protection--about 10 minutes or less.) Protection with the Bite Blocker lasts significantly longer (1.5 hours), but all of them must be applied frequently.

A synthetic insect repellent IR3535, provides protection of only 20 minutes to an hour. This product is less toxic than DEET and can be used with sunscreens (e.g., Avon Skin-So-Soft Bug Guard Plus IR3535 with Sunblock SPF 30.)

Of note, a new repellent that contains eucalyptus (Repel Lemon Eucalyptus Insect Repellent, Fite Bite Plant-Based Insect Repellent) offers protection that averages two hours and may be prove to be a good alternative, particularly for children.

Bayrepel (a piperidine derivative), a preparation used in Europe, may prove to be very protective.

The following products offer very little protection or none at all: Skin-So-Soft Bath Oil, all wristbands (including those that contain DEET or emit sound), garlic, and vitamin B1.

Use of Permethrin on 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, this agent 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 Mosquito Populations 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 three to four 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. A number of mosquito traps are now available that use various methods for repelling or attracting (typically with carbon dioxide) and trapping the insects (They should always be used outdoors--not indoors). Many traps can draw in significant numbers of mosquitoes, but 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. Different baits may be more or less effective, however, and some may even attract one species and not others.

For example, in one comparative study of three traps that used similar attractancts, after 20 hours the Magnet Liberty and Mosquito Trap MK01 attracted three-quarters of mosquitoes in a single area while the Sonic Web had attracted only a quarter. 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).

Of note, 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. And, unfortunately, they are effective at killing insects that help keep harmful insect pests in check.

Effective traps are expensive and they usually require electricity or propane, which adds to the cost.

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.

Other Preventive Measures

Additional preventive measures include:

• Wearing trousers and long-sleeved shirts, particularly at dusk. One survey suggested that this measure may significantly reduce the incidence of mosquito-born disease.
• Sleeping 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.
• Not wearing perfumes.
• Minimizing skin exposure after dusk.
• Washing hair at least twice a week.

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.) Smoke from burning certain plants, including ginger, beetlenut, and coconut husks, have also reduced mosquito infiltration, but the irritating and toxic effects on the eyes and lungs may be considerable. To date, no evidence shows much benefit, but such methods are not harmful.

Public Measures

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 (e.g., 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.

Natural Predators. A fish called Gambia Afghanis, which eats mosquito larva, is being used in waste water treatment plants in New York.

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.