As the warm temperatures continue, residents of Toronto engage in a number of outdoor activities such as picnics, barbecues, outdoor concerts, visits to cottages, hiking, camping or just relaxing in the backyard.  These activities increase their exposure to vectors such as mosquitoes. Furthermore, the warm weather results in an increase in the insect populations.  Some of these insects may transmit infections such as West Nile Virus.

During the summer months, particularly during mid-July to early September, infected mosquitoes may spread the West Nile Virus to humans through bites. Symptoms of West Nile Virus Infection may develop within 2 – 15 days after a person was bitten by a mosquito carrying the virus.    Symptoms may range from mild to severe.  The vast majority (about 80 per cent) of people who were bitten will show no symptoms; One in five will develop symptoms such as fever, headache, body aches, joint pains, vomiting, diarrhoea or a rash, but will usually recover completely on their own, although fatigue and weakness can last for weeks or months.  In rare cases (one in 150), infected people will develop more severe symptoms, including high fever, severe headache, muscle weakness, confusion, stiff neck, sudden sensitivity to light, numbness and paralysis

 Anyone can become infected with West Nile Virus but people older than 50 years of age, and those with medical conditions such as diabetes, cancer, heart disease, kidney disease or weakened immune systems have a greater chance of developing a serious illness.   Children typically do not develop severe illness.

There is no vaccine or specific antiviral treatments for West Nile Virus infection. In severe cases, supportive treatment such as intravenous fluids, breathing support and pain medication may be given.

 An Ounce of Prevention

The best way to prevent getting infected with West Nile Virus is to avoid getting bitten by mosquitoes in the first place. If going outdoors during dusk to dawn when the mosquitoes are usually most active, wear light-coloured, loose-fitting clothing, long sleeve shirts, long pants and socks.  Use an insect repellent (lotion or spray) containing DEET or icaridin.  Be careful to read and follow the recommendations on the label of the repellant.  The product should be used in the right concentration, depending on age.  Ask a pharmacist for help if necessary. Do not use insect repellent on infants younger than six months old; use a mosquito net over cribs and strollers instead.

Other mosquito repellent products include soybean oil, citronella oil, mixture of essential oils (lemon, camphor, eucalyptus, geranium, pine needle) and clip-on devices containing metofluthrin.  These repellents should also be used safely.

 Do not provide breeding places for mosquitoes. Remove stagnant water sources where  they can lay eggs and keep your surroundings clean and clear of clutter:

• Once a week, empty standing water from objects such as flower pots, planters, buckets, wheelbarrows, tires, toys, and pools.
• Change the water in bird baths often.
• Keep rainwater barrels covered.
• Clean and chlorinate swimming pools and wading pools.
• Clean eaves troughs regularly.
• Keep bushes and shrubs neatly trimmed.

Make sure your home has tight-fitting screens on windows and doors and repair any holes in screens to keep mosquitoes out.

If you think that you have contracted West Nile Virus, contact your health care provider.

(Heather Aspinall Robinson is a communicable disease specialist.)