West Nile Virus
Know the risks of the West Nile Virus
West Nile virus first emerged in the United States in the New York metropolitan area in the fall of 1999. Since then, the virus, which can be transmitted to humans by the bite of an infected mosquito, has quickly spread across the country. Mild cases of West Nile infections may cause a slight fever or headache. More severe infections are marked by a rapid onset of a high fever with head and body aches, disorientation, tremors, convulsions and, in the most severe cases, paralysis or death. Usually symptoms occur from three to 14 days after the bite of an infected mosquito. Persons at the highest risk for serious illness are those 50 years of age or older.
The best way to prevent West Nile encephalitis and other mosquito-borne illnesses is to reduce the number of mosquitoes around your home and neighborhood and to take personal precautions to avoid mosquito bites.
West Nile origins in Illinois
West Nile virus was first identified in Illinois in September 2001 when laboratory tests confirmed its presence in two dead crows found in the Chicago metropolitan area. In 2002, birds, mosquitoes and horses in 100 of the state's 102 counties were reported positive for West Nile virus and the first human cases and deaths from West Nile virus illness in Illinois were reported in August 2002. By the end of the year, the state lead the nation with more than 800 human cases and 62 deaths. The Illinois Department of Public Health (IDPH) maintains a sophisticated disease surveillance system to monitor animals and insects that can potentially carry the virus: dead crows and blue jays, mosquitoes and horses. Mosquitoes can either carry the virus or get it by feeding on infected birds.
West Nile Virus Prevention
Keep mosquitoes from bugging you:
- Minimize time outdoors between dusk to dawn.
- Wear long-sleeve shirts and long pants.
- Avoid dark colored clothing.
- Avoid using perfumes and body lotions.
- Sparingly apply mosquito repellent with DEET
Protect your home:
- Keep drains and culverts free of grass clippings, weeds and trash so water will drain properly.
- Empty standing water from:
- Potted plants
- Bird baths
- Pet dishes
- Wading pools
- Old tires
- Repair torn screens.
- Clean gutters.
- Use Bti donut in areas standing water can not be eliminated. Larvicide available at garden centers.
Avoid Mosquitoes in Your Water Garden
- Add fish. Any fish–including goldfish–will feed on mosquito larvae.
- Dragonfly and damselfly larva in the water are good predators.
- Construct ponds with vertical sides. Sloping sides encourage mosquito breeding.
- Add a fountain or waterfall. Moving water deters mosquitoes.
- Remove fallen leaves and debris regularly.
- If fish are not present, use Bti “donuts” containing a bacterium, Bacillus thuringiensis israelensis or “Bti.”
- Bti donuts control larvae for 30 days and each donut treats 100 sq. ft.
- Bti donuts may be broken to treat smaller areas. Water treated with Bti is safe for fish, plants, wildlife and pets.
- Bti donuts may be used anywhere water cannot be drained, even tree holes.
Gardens and Mosquitoes
Mosquitoes lay eggs in stagnant water. The key to controlling mosquitoes is in controlling the places where they breed.
- Place window screen wire securely over top of rain barrels to keep leaves and mosquitoes out. Or use mosquito Bti donuts.
- Never leave water in sprinkling cans or buckets for more than one day.
- Check garden statuary for places water may collect. Add holes for drainage or empty regularly.
- Make sure stored pots are not collecting water. Even water in a tin can may breed mosquitoes.
- Clean and replenish bird baths and pet water bowls at least twice a week.
- Empty saucers under flowerpots regularly.
What doesn’t work to control mosquitoes:
- Mosquito repelling plants
- Bug zappers
- Electronic emitters
- Light traps/carbon dioxide traps
Insect Repellent Use and Safety
Why should I use insect repellent?
- Insect repellents help people reduce their exposure to mosquito bites that may carry potentially serious viruses such as West Nile virus, and allow them to continue to play and work outdoors.
When should I use mosquito repellent?
- Apply repellent when you are going to be outdoors and will be at risk for getting bitten by mosquitoes.
What time of day should I wear mosquito repellent?
- Many of the mosquitoes that carry the West Nile virus are especially likely to bite around dusk and dawn. If you are outdoors around these times of the day, it is important to apply repellent. In many parts of the country, there are mosquitoes that also bite during the day, and these mosquitoes have also been found to carry the West Nile virus. The safest decision is to apply repellent whenever you are outdoors.
How often should repellent be reapplied?
- Follow the directions on the product you are using in order to determine how frequently you need to reapply repellent. Sweating, perspiration or getting wet may mean that you need to re-apply repellent more frequently. If you are not being bitten, it is not necessary to re-apply repellent. Repellents containing a higher concentration of active ingredient (such as DEET) provide longer-lasting protection.
Should I wear repellent while I am indoors?
- Probably not. If mosquitoes are biting you while you are indoors, there are probably better ways to prevent these bites instead of wearing repellent all the time. Check window and door screens for holes that may be allowing mosquitoes inside. If your house or apartment does not have screens, a quick solution may be to staple or tack screening (available from a hardware store) across the windows. In some areas community programs can help older citizens or others who need assistance.
How does mosquito repellent work?
- Female mosquitoes bite people and animals because they need the protein found in blood to help develop their eggs. Mosquitoes are attracted to people by skin odors and carbon dioxide from breath. Many repellents contain a chemical, N,N-diethyl-m-toluamide (DEET), which repels the mosquito, making the person unattractive for feeding. DEET does not kill mosquitoes; it just makes them unable to locate us. Repellents are effective only at short distances from the treated surface, so you may still see mosquitoes flying nearby. As long as you are not getting bitten, there is no reason to apply more DEET.
Which mosquito repellent works the best?
- The most effective repellents contain DEET (N,N-diethyl-m-toluamide), which is an ingredient used to repel pests like mosquitoes and ticks. DEET has been tested against a variety of biting insects and has been shown to be very effective. The more DEET a repellent contains the longer time it can protect you from mosquito bites. A higher percentage of DEET in a repellent does not mean that your protection is better—just that it will last longer. DEET concentrations higher than 50% do not increase the length of protection.
How does the percentage of DEET in a product relate to the amount of protection it gives?
- Based on a recent study:
A product containing 23.8% DEET provided an average of 5 hours of protection from mosquito bites.
A product containing 20% DEET provided almost 4 hours of protection.
A product with 6.65% DEET provided almost 2 hours of protection.
Products with 4.75% DEET and 2% soybean oil were both able to provide roughly 1 and a half hour of protection. Choose a repellent that provides protection for the amount of time that you will be outdoors. A higher percentage of DEET should be used if you will be outdoors for several hours while a lower percentage of DEET can be used if time outdoors will be limited. You can also re-apply a product if you are outdoors for a longer time than expected and start to be bitten by mosquitoes.
Why does CDC recommend using DEET?
- DEET is the most effective and best-studied insect repellent available. (Fradin, 1998). Studies using humans and mosquitoes report that only products containing DEET offer long-lasting protection after a single application.(Fradin and Day, 2002. See Publications page.)
Are non-DEET repellents effective (e.g. Skin-So-Soft, plant-based repellents)?
- Some non-DEET repellent products which are intended to be applied directly to skin also provide some protection from mosquito bites. However, studies have suggested that other products do not offer the same level of protection, or that protection does not last as long as products containing DEET. A soybean-oil-based product has been shown to provide protection for a period of time similar to a product with a low concentration of DEET (4.75%) (Fradin and Day, 2002.).
- People should choose a repellent that they will be likely to use consistently and that will provide sufficient protection for the amount of time that they will be spending outdoors. Product labels often indicate the length of time that protection that can be expected from a product. Persons who are concerned about using DEET may wish to consult their health care provider for advice. The National Pesticide Information Center (NPIC) can also provide information through a toll-free number, 1-800-858-7378 or http://npic.orst.edu/ .
I'm confused. None of the products in the store says "DEET."
- Most insect repellents that are available in stores are labeled with the chemical name for DEET. Look for N,N-diethyl-m-toluamide or, sometimes, N,N-diethly-3-methylbenamide. Choose a repellent that offers appropriate protection for the amount of time you will be outdoors. A higher percentage of DEET should be used if you will be outdoors for several hours while a lower percentage of DEET can be used if time outdoors will be limited.
Is DEET safe?
- Yes, products containing DEET are very safe when used according to the directions. Because DEET is so widely used, a great deal of testing has been done. When manufacturers seek registration with the U.S. Environmental Protection Agency (EPA) for products such as DEET, laboratory testing regarding both short-term and long-term health effects must be carried out. Over the long history of DEET use, very few confirmed incidents of toxic reactions to DEET have occurred when the product is used properly. (From the National Pesticide Information Center [NPIC], EPA re-registration eligibility decision. See http://npic.orst.edu/factsheets/DEETgen.pdf .)
What are some general considerations to remember in order to use products containing DEET safely?
- Always follow the recommendations appearing on the product label.
Use enough repellent to cover exposed skin or clothing. Don't apply repellent to skin that is under clothing. Heavy application is not necessary to achieve protection.
Do not apply repellent to cuts, wounds, or irritated skin.
After returning indoors, wash treated skin with soap and water.
Do not spray aerosol or pump products in enclosed areas.
Do not apply aerosol or pump products directly to your face. Spray your hands and then rub them carefully over the face, avoiding eyes and mouth.
Use on Children
How should products containing DEET be used on children?
- No definitive studies exist in the scientific literature about what concentration of DEET is safe for children. No serious illness has arisen from use of DEET when used according the manufacturer’s recommendations. The American Academy of Pediatrics has recommended that a cautious approach is to use products with a low concentration of DEET, 10% or less, on children aged 2 - 12. Most guidelines cite that it is acceptable to use repellents containing DEET on children over 2 years of age. Other experts suggest that it is acceptable to apply repellent with low concentrations of DEET to infants over 2 months old.
- Repellent products that do not contain DEET are not likely to offer the same degree of protection from mosquito bites as products containing DEET. Non-DEET repellents have not necessarily been as thoroughly studied as DEET, and may not be safer for use on children.
- Parents should choose the type and concentration of repellent to be used by taking into account the amount of time that a child will be outdoors, exposure to mosquitoes, and the risk of mosquito-transmitted disease in the area. Persons who are concerned about using DEET or other products on children may wish to consult their health care provider for advice. The National Pesticide Information Center (NPIC) can also provide information through a toll-free number, 1-800-858-7378 or http://npic.orst.edu.
- Always follow the recommendations appearing on the product label when using repellent.
When using repellent on a child, apply it to your own hands and then rub them on your child. Avoid children's eyes and mouth and use it sparingly around their ears.
Do not apply repellent to children's hands. (Children tend to put their hands in their mouths.)
Do not allow young children to apply insect repellent to themselves; have an adult do it for them. Keep repellents out of reach of children.
Do not apply repellent to skin under clothing. If repellent is applied to clothing, wash treated clothing before wearing again. Using repellents on the skin is not the only way to avoid mosquito bites. Children and adults can wear clothing with long pants and long sleeves while outdoors. DEET or other repellents such as permethrin can also be applied to clothing (don’t use permethrin on skin), as mosquitoes may bite through thin fabric. Mosquito netting can be used over infant carriers. Finally, it may be possible to reduce the number of mosquitoes in the area by getting rid of containers with standing water that provide breeding places for the mosquitoes.
Is DEET safe for pregnant or nursing women?
- There are no reported adverse events following use of repellents containing DEET in pregnant or breastfeeding women.
Are there any risks due to using repellents containing DEET?
- Use of these products may cause skin reactions in rare cases. If you suspect a reaction to this product, discontinue use, wash the treated skin, and call your local poison control center. There is a new national number to reach a Poison Control Center near you: 1-800-222-1222.
- If you go to a doctor, take the product with you. Cases of serious reactions to products containing DEET have been related to misuse of the product, such as swallowing, using over broken skin, and using for multiple days without washing skin in between use, for example. Always follow the instructions on the product label.
Pets and Livestock
Can West Nile virus infect dogs and cats?
- Yes, however, infection rates in epidemic areas are low. WNV does not usually cause severe illness.
Which dogs and cats are likely to be the most susceptible?
- Based on the most recent animal cases seen at the University of Illinois College of Veterinary Medicine Veterinary Diagnostic Laboratory, young, old, and immune-compromised pets would seem to be at a higher risk.
How do dogs and cats become infected with West Nile virus?
- The same way humans become infected: by the bite of infectious mosquitoes. It is possible that dogs and cats could become infected by eating dead infected animals such as birds, but this is unproven.
How can I protect my pet?
- Keep pets indoors during peak mosquito hours--dawn, dusk, and early evening.
- Eliminate standing water around your home.
- Prevent pets from coming into contact with dead birds or squirrels that may have died as the result of the virus.
- Contact your local veterinarian if your pet exhibits any neurological signs, such as incoordination, depression, decreased appetite, difficulty walking, tremors, abnormal head posture, circling, and convulsions.
- Use only approved mosquito repellent on your pet; make sure to read the label first to determine if the product is approved for use in pets.
Can I use a mosquito insect repellent meant for humans on my pet?
- No, only approved mosquito repellents should be used on your pet, make sure to read the label first to determine if the product is approved for use in pets and then follow label instructions for applications.
Can I use DEET (N,N-diethyl-m-toluamide, N,N-diethyl-3-methylbenzamide) mosquito repellent on my pet?
- The use of DEET on animals is not recommended and should be avoided. DEET has been associated with serious adverse effects when used on dogs and cats. Citrus oil extracts and other essential oils are also not recommended due to the extreme sensitivity of some animals to these products.
What are the signs of WNV in dogs?
- Neurological signs are similar to those seen in horses, such as incoordination, depression, decreased appetite, difficulty walking, tremors, abnormal head posture, circling, and convulsions. These signs can mimic other diseases; therefore, it is very important to contact your veterinarian if your pet is exhibiting any of these signs.
Is there a vaccine available for dogs and cats?
- No, there is currently only a vaccine available for horses.
What is the treatment for WNV in pets?
- There is no specific treatment other than supportive care provided by your veterinarian.
Can pets transmit the WNV to humans or other pets?
- There is no documented evidence that animal-to-animal or animal-to-person transmission can occur. There is no reason to destroy an animal because it has been infected with WNV.
Credit: Portions of this content first appeared on Extension's Preventing West Nile Virus website.