West Nile Virus

The West Nile virus belongs to a family of viruses called Flaviviridae and was first isolated(1937) in the West Nile province of Uganda. The first West Nile virus infection in North America occurred in the New York City area in the summer of 1999. In Canada, the virus was first found in birds in Ontario in 2001 and the first human case of West Nile virus occured in Ontario in September 2002. During 2002, more than 4,000 people in North America became ill after being infected with West Nile virus.

How do people get infected with West Nile virus?

Most people infected with West Nile virus got it from the bite of an infected mosquito. A mosquito becomes infected when it feeds on a bird that is infected with the virus. The mosquito can then pass the virus to people and animals by biting them. Probably less than 1% of mosquitoes in any given area are infected with West Nile virus. This means the risk of being bitten by an infected mosquito is low. But, it could happen to anyone in areas where West Nile virus is active.

There have been cases in Canada and the United States of West Nile virus being spread through blood transfusions and organ transplants. However, there is no evidence to suggest that people can get West Nile virus by touching or kissing someone who is infected, or from being around a health care worker who has treated an infected person. There is no evidence that the virus can pass directly from infected animals(horses, pets, etc.)to people.

Who is most at risk?

Many people infected with West Nile virus have mild symptoms,or no symptoms at all. Although anybody can have serious health effects, it is people with weaker immune systems that are ay greater risk for serious complications. This higher risk group includes:

  • People over the age of 40
  • People with chronic diseases, such as cancer, diabetes or heart disease
  • People that require medical treatment that may weaken the immune system(such as chemotherapy or corticosteroids)

Although individuals with weaker immune systems are at greater risk, West Nile virus can cause severe complications for people of any age and any health status. This is why it is so important to reduce the risk of getting bitten by mosquitoes.

The symptoms of West Nile virus infection

Symptoms usually appear within 2 to 15 days. The type and severity of symptoms varies from person to person. Symptoms of mild disease include:

  • Flu-like symptoms
  • Fever
  • Headache
  • Body aches
  • Rash

Persons with weaker immune systems or chronic disease, are at greater risk of developing more serious complications, including meningitis(infection of the covering of the brain) and encephalitis(infection of the brain itself). Tragically, these conditions can be fatal. Symptoms of more severe disease include:

  • Severe headache
  • High fever
  • Stiff neck
  • Nausea/vomiting
  • Sleepiness
  • Confusion
  • Loss of consciousness
  • Lack of coordination
  • Muscle weakness and paralysis

Is there a treatment for West Nile virus infection?

Unfortunately, as with most viruses, there is no specific treatment or medication for West Nile virus. Serious cases are treated with supportive treatments such as intravenous fluids, close monitoring and other medications that help fight the complications of the infection. Obviously such cases may require hospitalization. Currently, there is no vaccine available to protect against West Nile virus, although there is a lot of research going on in this area.

How is West Nile virus infection confirmed?

If a doctor suspects that a person may have West Nile virus, based on the history of symptoms, especially in an area where West Nile virus is present, there are specific blood tests which can confirm the infection.

Mosquito bite prevention

The best way to reduce the risk of infection is to try to prevent mosquito bites. If West Nile virus activity is detected in your area:

  • Limit time spent outdoors at dawn and dusk, when many mosquitoes are most active
  • Wear light-colored protective clothing such as long-sleeved shirts, long pants, and a hat when outdoors in areas where mosquitoes are present
  • A long sleeve shirt with snug collar and cuffs is best. The shirt should be tucked in at the waist. Socks should be tucked over pants, hiking shoes or boots
  • Light colored clothing is best because mosquitoes tend to be more attracted to dark colors
  • When going outdoors use insect repellents that contain DEET or other approved ingredients
  • Make sure that door and window screens fit tightly and have no holes that may allow mosquitoes indoors
  • To avoid insect bites, do not use scented soaps, perfumes or hair sprays on your children
  • For young babies, mosquito netting is very effective in areas where exposure to mosquitoes is likely. Netting may be used over infant carriers or other areas where young children are placed

About DEET:

DEET(N,N-diethyl-m-toluamide or, N,N-diethly-3-methylbenamide)was approved as a repellent for public use in 1957. Since then, it has appeared in more than 200 products, and is used by about 21% of households, 30% of adults and 34% of children. Studies have shown that:

  • A product containing 23.8% DEET provides about 5 hours of protection from mosquito bites.
  • A product containing 20% DEET provides almost 4 hours of protection
  • A product with 6.65% DEET provides almost 2 hours of protection
  • Products with 4.75% DEET provides about 1 and a half hour of protection

DEET safety concerns

DEET is generally used without any problems. There have been rare reports of side effects usually, as a result over-use. The American Academy of Pediatrics has recommended a concentration, of 10% or less for children aged 2 - 12. Most experts agree that DEET can be safely used in children over 2 years of age, but if there is a risk of West NIle virus then, DEET can be used in children 6 months or older.

Alternatives to DEET?

Unfortunately, there is no evidence that non-DEET repellents are as effective or safer than as those containing DEET. Citronella has mild repellent properties, but DEET is significantly more effective. Therefore, when repellent is being used to prevent West Nile virus, DEET should be used. Certain products containing citronella have a limit on the number of applications allowed per day. Read the product label before using. Products containing citronella and lavender are currently under re-evaluation.
Products with 2% soybean oil are able to provide about 1 and a half hour of protection(the equivalent of 4.75% DEET).
The manufacturers of a recently released natural based product(non-DEET)containing lemon eucalyptus plant claim that this protects up to 2 hours against mosquitoes.
Electromagnetic and ultrasound devices are not effective in preventing mosquito bites.

IN CANADA THE FOLLOWING NON-DEET PRODUCTS ARE RECOGNIZED AS REPPELLENTS:
(taken form Health Canada web site):

  • P-menthane 3,8-diol: A product containing this active ingredient was recently registered in Canada and thus meets all the modern safety standards. It provides up to two hours of protection against mosquitoes. This product cannot be used on children under three years of age. It can be applied two times per day.
  • Soybean oil: Registered products containing soybean oil provide between one to 3.5 hours of protection against mosquitoes, depending on the product. Products containing soybean oil were recently registered and thus meet all the modern safety standards.
  • Citronella and lavender: Registered products containing citronella protect people against mosquito bites from 30 minutes to two hours. The registered lavender product repels mosquitoes for approximately 30 minutes. These products cannot be used on infants and toddlers under two years of age. Based on animal studies, citronella-based products appear to be potential skin sensitizers. Therefore, allergic reactions may occur in some individuals.

Summary of DEET use based on age:

Children under 6 months of age DO NOT use personal insect repellents containing DEET on infants.
Children aged 6 months to 2 years

In situations where a high risk of complications from insect bites exist, the use of one application per day of DEET may be considered for this age group. The least concentrated product (10% DEET or less) should be used. As with all insect repellents, the product should be applied sparingly and not be applied to the face and hands. Prolonged use should be avoided.

Children between 2-12 years of age

The least concentrated product (10% DEET or less) should be used. Do not apply more than three times per day. Prolonged use should be avoided.

Adults and Individuals 12 Years of Age or Older:

Studies show that products with lower than 30% concentrations of DEET are as effective as the high concentration products, but they remain so for shorter periods of time. Products containing no more than a 30% concentration of DEET will provide adults with sufficient protection. Re-apply after these protection times have elapsed if necessary. Bottom line.. as low a concentration as possible.

DEET combined with a sunscreen?

Sunscreen preparations are usually applied repeatedly to the skin to prevent sun exposure. This "repeated" application may result in overexposure to DEET, which should be applied sparingly. So these combined preparations should not be used.

Is DEET safe for pregnant or nursing women?

According to the CDC, there are no reported adverse events following use of repellents containing DEET in pregnant or breastfeeding women.

Precautions when using DEET:

  • Read and carefully follow all directions before using the product
  • Young children should not apply DEET to themselves
  • Wear long sleeves and pants when possible and apply repellent to clothing
  • Apply DEET sparingly only to exposed skin and avoid over application. Do not use DEET underneath clothing
  • Do not use DEET on the hands of young children and avoid the eye and mouth areas
  • Do not apply DEET over cuts, wounds, or irritated skin
  • Wash treated skin with soap and water upon returning indoors. Also, wash treated clothing
  • Avoid using sprays in enclosed areas
  • Do not apply aerosol or pump products directly to the face. Spray your hands and then rub them carefully over the face(avoid eyes and mouth)
  • Do not use DEET near food
  • Keep repellents out of reach of children.
  • Do not apply to infants under 6 months of age

Repellent use at schools

Should parents spray insect repellent on their children before they go to school?

According to the CDC, whether children spend time outside during the school day should determine the need for applying repellent.If children will be spending time outdoors (for example, in recreational activities, walking to and from school), parents may wish to apply repellent. Should children be given repellent to use during the day?

This depends on the age and maturity of the child. As with many other chemicals, care should be taken that DEET is not misused or swallowed. Also, parents should be aware of school policies and procedures regarding bringing/using repellents to school.

Reducing the mosquito population around your home:

Mosquitoes lay eggs in standing water and it takes about 4 days for the eggs to grow into adults that are ready to fly. Even a small amount of water, like in a saucer under a flower pot, is enough to act as a breeding ground. As a result, it is important to eliminate standing water as much as possible around your property. Here are some tips:

  • Regularly drain standing water from items like pool covers, saucers under flower pots, pet bowels, pails, recycle bins, garbage cans etc.
  • Drill holes in the bottom of recycling bins
  • Change(or empty) the water in wading pools, bird baths, pet bowls and livestock watering tanks twice a week
  • Turn over plastic wading pools and wheel barrels when not in use
  • Clean and chlorinate your swimming pools. A pool left unattended can produce a large number of mosquitoes
  • Landscape your garden as necessary to eliminate stagnant waters(mosquitoes can breed even in puddles of water that last for more than 4 days
  • Get rid of unused items that have a tendency to collect water including old tires
  • Cover rain barrels with screens
  • Clean eaves troughs(roof gutters)regularly to prevent clogs that can trap water
  • If you have an ornamental pond, consider getting fish that will eat mosquito larvae

SOURCES: CDC, HEALTH CANADA, AMERICAN ACADEMY OF PEDIATRICS(AAP)
RELATED LINKS:
CDC
HEALTH CANADA
DR.PAUL's FACT SHEET ON WEST NILE VIRUS
DR.PAUL's FACT SHEET ON MOSQUITO BITE PREVENTION

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