Your Health

Fight the bite

Guarding against mosquitoes can protect you from West Nile virus.

Guarding against mosquitoes can protect you from West Nile virus.

BY LINDA COOTE
Winnipeg Health Region
Wave, Summer 2009

What is West Nile virus?

West Nile virus (WNv) is a flavivirus commonly found in Africa, West Asia and the Middle East. The virus can infect humans, birds, mosquitoes, horses and some other mammals.The virus is transmitted by mosquitoes. Most people who are bitten by an infected mosquito do not become ill, and for those who do, the symptoms are usually mild. In some cases, the virus causes serious illness and sometimes death. Human cases of West Nile virus were first detected in southern Manitoba in summer 2003.

What are the symptoms of WNv infection?

Usually, people infected by West Nile virus have no symptoms and do not become ill. Of those who do become ill, most will develop West Nile virus non-neurological syndrome, an illness with symptoms such as fever, headache, fatigue and body aches. Less frequently, the virus can cause more serious illness (West Nile neurological syndrome), including encephalitis, an inflammation of the brain. People with pre-existing medical conditions and older adults are more at risk for severe illness. However, illness has occurred in all age groups. Encephalitis can have serious complications. These complications may include weakness, paralysis, confusion, coma or death.

Milder symptoms of West Nile virus nonneurological syndrome usually improve without medical care and may last a few days. Anyone experiencing severe symptoms (e.g., persistent high fever, muscle weakness, headache) should seek medical attention promptly for diagnosis and care.

Who is at risk for getting West Nile encephalitis?

All residents of or travellers to areas where WNv activity has been reported are at risk. While illness has occurred in all age groups, people with pre-existing medical conditions and older adults (50 years of age or older) are at greater risk for serious health effects.

What can I do to reduce my risk of becoming infected with West Nile virus?

Mosquitoes need water to lay eggs. Mosquito eggs left in stagnant water, even small amounts allowed to stand for a week or more, can develop into adult mosquitoes. Reducing or eliminating standing water is an effective and economical way to control mosquitoes and something all Manitobans can do around their homes:

  • Eliminate sources of standing water in your yard (e.g., flowerpots, watering cans, wheelbarrows, and puddles). Items that must remain in your yard, such as boats and gardening containers, should be covered or stored upside down.
  • Adjust tarps over grills, firewood piles, boats and other objects to avoid the collection of water.
  • Drill holes in the bottom of water-collecting objects and containers that must be left outdoors, such as flower pots or tire swings to drain any water. Consider replacing the swing with another type that does not collect water.
  • Cover any garbage, recycling or composting containers, to prevent water from collecting.
  • Replace water in birdbaths and outdoor pet dishes once every week.
  • Ensure that openings in rain barrels are covered with mosquito screening or tightly sealed around the downspout. If a rain barrel is not screened, add 1/2 cup of household bleach to it once a week to get rid of any mosquito eggs, or empty the rain barrel if the water is more than a week old.
  • Keep swimming pools aerated, clean and chlorinated, even if they are not being used. Dump any water that collects on swimming pool covers.
  • Turn over plastic wading pools when not in use. Change the water in wading pools at least once a week.
  • Keep eavestroughs and gutters clear of debris to prevent standing water.
  • Check under shrubbery and lawn coverings for hidden containers that may contain water.
  • Use landscaping to eliminate water that collects in low areas of your property.
  • Trim vegetation around your property, particularly around the foundation of your house. Weeds, tall grass and shrubbery provide ideal resting sites for adult mosquitoes.
  • Avoid over-watering your lawn or garden to the point where there is standing water that lasts for more than a few days.
  • Repair any leaks from outdoor water pipes, joints or hoses. Replace washers on outdoor taps that drip.
  • Make sure household and cottage drainage systems are working properly and are not blocked. Check that water is not collecting in septic tank discharge fields.

What is the safest way to use personal insect repellents?

Here are some tips for using insect repellents:

  • Always read the entire label carefully before using. Follow all of the label directions, including restrictions for use on young children and the maximum number of applications allowed per day.
  • Apply the repellent sparingly, and only on exposed skin surfaces or on top of clothing. Do not use under clothing. Heavy application and saturation are unnecessary for effectiveness. Repeat applications only as necessary.
  • Do not get in eyes. If you do get repellent in your eyes, rinse immediately with water.
  • Do not use the repellent on open wounds, or if your skin is irritated or sunburned.
  • Avoid breathing spray mists and never apply sprays inside a tent. Use only in well-ventilated areas. Do not use near food.
  • Wash treated skin with soap and water when you return indoors or when protection is no longer needed.
  • Keep all insect repellent containers out of the reach of children. Always supervise the application on children. Avoid applying repellent to children's hands to reduce the chance of getting the repellent in their eyes and mouths.
  • If you are concerned that you are sensitive to a product, apply the product to a small area of skin on your arm and wait 24 hours to see if a reaction occurs.
  • Choose a product that meets your needs. For example, if you plan to be outdoors for a short period of time, choose a product with a lower concentration of repellent and repeat application only if you need a longer protection time.

Health Canada regulations allow the following concentrations for different age groups:

  • Up to 30 per cent concentration of DEET for adults and children over 12 years of age. Each application should be effective for six hours against mosquitoes.
  • Up to 10 per cent concentration for children aged two to 12, applied up to three times daily. Each application should be effective for three hours against mosquitoes.
  • Up to 10 per cent concentration for children aged six months to two years, applied no more than once daily. It offers three hours of protection against mosquitoes. Do not apply on face and hands.
  • Do not use personal insect repellents containing DEET on infants under six months. Use a mosquito net when the child is in a crib, playpen or stroller outdoors.
  • Sunscreen and insect repellents can be combined. Follow the instructions on the package for proper applications of each product. Apply the sunscreen first, followed by the insect repellent.

For More Information

For more information, visit Manitoba Health and Healthy Living's website
at www.gov.mb.ca/health/wnv

Linda Coote is a registered nurse and a manager with the Winnipeg Health Region's Health Links - Info Santé.

Wave

About Wave

Wave is published six times a year by the Winnipeg Health Region in cooperation with the Winnipeg Free Press. It is available at newsstands, hospitals and clinics throughout Winnipeg, as well as McNally Robinson Books.

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