West Nile virus: What you should know

Mosquito bites aren’t much fun — but sometimes we underestimate how dangerous they can be. The recent outbreak of West Nile virus in the U.S. has officials worried about these disease-carrying insects.

In an August 29, 2012 news release, the U.S. Centers For Disease Control and Prevention (CDC) reported it has seen 1,590 cases so far this year including 66 deaths — that’s a 40 per cent jump in the number of cases from the previous week. By far, the highest number of cases have been reported in Texas where nearly half of all cases and the majority of deaths have occurred — causng some municipalities such as Dallas to declare a state of emergency. Forty-one states have reported cases of West Nile virus, but five states — Texas, Mississippi, Louisiana, South Dakota, and Oklahoma — account for about 75 per cent of cases.

“These data show that the number of West Nile virus disease cases in people has risen dramatically in recent weeks,” said Dr. Lyle Petersen of the CDC in an August 22 teleconference. “And indicate that we’re in the midst of one of the largest West Nile virus outbreaks ever seen in the United States.”

And don’t expert the numbers to wane any time soon, say experts.

“I’m not convinced that we have peaked. We may have plateaued,” said Dr. David Lakey, commissioner of the Texas Department of State Health Services, in an August 29 CDC teleconference.

How does these stats stack up to previous years? In 2011, the country saw 712 confirmed cases in total — down from 2010’s total of 1,021 and roughly equivalent to 2009’s 720 cases.

What about Canada? As of August 18, 62 clinically diagnosed cases have been reported to the Public Health Agency of Canada (PHAC). In 2011, experts logged a total of 110 cases — 69 in Ontario and 41 in Quebec. In 2010, there were only four cases reported and 2009 saw just 13. We can thank winter’s warm temps and that early spring we enjoyed for helping mosquitoes settle in.

And bad news for Torontonians: many of Ontario’s 82 confirmed or probable cases were in the city, according to an August 28 report from Public Health Ontario.

Is the U.S. outbreak heading north? No one seems to be pushing the panic button here in Canada though officials in some parts of the country are keeping their eyes open. So far, around 320 pools of mosquitoes across the country have tested positive for West Nile virus. Some experts warn that West Nile cases are on the rise in some areas.

“I suspect this year will be another outbreak year maybe even as big as 2007 or 2003 given the early activity in Ontario,” said Dr. Bonnie Henry, medical director of communicable disease prevention and control services at the B.C. Centre for Disease Control in an article on CBC News.

The numbers change on a daily basis, and will likely continue to climb for a while longer. Right now is peak season for mosquitoes, so experts will be keeping a close eye on the issue in weeks to come.

Statistics may not tell the whole story

However, the reported cases don’t always give us an accurate view of the “big picture”. The West Nile virus has two forms: Neurological Syndrome (also known as neuroinvasive) and Non-Neurological Syndrome (non-neuroinvasive or West Nile Fever). As the name suggests, the neurological form is more severe and affects the nervous system — such as inflammation in the brain, membrane around the brain or spinal cord.

Experts say only 1 in 150 people who are infected with West Nile Virus will develop severe neurological symptoms. In the U.S outbreak, more than half of all reported cases are the neuroinvasive form.

The non-neurological form — which the majority of sufferers contract — has milder, flu-like symptoms. (That is, if they experience symptoms at all — experts say only 20 per cent of people who are infected develop symptoms.) Doctors are required to notify experts about any cases of West Nile virus, but they can only record the people who seek treatment.

While officials in Canada certainly aren’t in disaster mode, they do warn that there are steps we should be taking to reduce our chances of catching the virus.

Tips to help prevent West Nile Virus

As you’ve likely heard, the West Nile virus mostly spreads through mosquitoes. When a certain species of mosquito know as Culex bites an infected bird, it picks up the virus and can transmit it to any animal or human it bites. Avoiding the bugs and denying them the places to breed are the best strategies we can use against the problem.

Here’s what you can do to help reduce your risk:

Consider staying inside during peak times. Dawn, dusk and early evening are prime time for mosquito bites. If you want to venture outdoors, you’ll want to take more precautions — such as sitting in an area enclosed by a netting.

Cover up. Long sleeves, pants and socks deny mosquitoes skin surface area to bite. Mosquito season typically starts mid-April and lasts until the first hard frost in September or October — so warm weather isn’t conducive for this strategy. Keep in mind that mosquitoes can bite through this clothing, so you’ll either want to don something heavier or spray your clothes with repellent.

Consider wearing an inspect repellent containing DEET or other approved ingredients. Other active ingredients include picaridin, oil of lemon eucalyptus (or its synthetic form, PMD) and IR3535. You’ll want to exercise some caution, however — don’t let kids handle these chemicals, don’t apply them under clothing and wash any treated clothing or skin when you go back indoors. Avoid using repellents that contain permethrin directly on skin.

Remember, strength doesn’t mean better protection. As with sunscreen, a higher number means you’ll be protected for longer. (The CDC has a good overview of insect repellents for more information.)

Repair your screens. Keep mosquitoes out of your home or cottage by ensuring that windows and doors have properly fitting screens with no holes or tears.

Another place that needs a screen: a baby carrier or play yard should be covered by a mosquito net.

Prevent standing water. Pools of stagnant water make ideal breeding grounds for mosquitoes — that’s where they like to lay their eggs. Check your home and property for any place water collects such as garbage cans, wheel barrows and pool. The water should be drained on a regular basis — at least twice a week.

Change water on a regular basis. The twice a week rule also applies to items that are meant to hold water. Regularly change the water in birdbaths, wading pools and pet water dishes too.

Keep it covered. Saving rainwater for your garden? No need to dump it out — just make sure it’s covered with a screen.

Clean your eaves troughs. Clogs can trap water too so keep everything moving.

Keep water moving. If you’re planning on putting a water feature or pond in your yard, make sure to buy one with an aerator. Moving water will deter mosquitoes. Another option: add some fish.

What about pesticides? Experts note that only trained professionals should handle them, and it’s up to communities to implement mosquito control measures.  Over-the-counter pesticides for general use will do little to combat mosquitoes.

Spotting the symptoms

Who is at most risk? Experts say anyone of any age can become infected. There’s no medical treatment for the virus – only your immune system. The younger and healthier you are, the better able you are to fight off the infection. Like the flu, West Nile virus is more of a danger to people who have a weakened immune system or other health issues.

How can you spot the symptoms?  The mild form often doesn’t present with any symptoms, but the effects of West Nile virus can often be felt two to 15 days after being bitten. Symptoms can include fever, headache, body aches, a rash and swollen lymph nodes. The virus can last for days or weeks.

How can you tell if the brain is affected? Warning signs of the potentially dangerous neurological syndrome include severe headache, high fever, stiff neck, vomiting, drowsiness, confusion, loss of consciousness, muscle weakness and paralysis — depending on what part of the nervous system is affected. Experts warn that people experiencing these symptoms — especially the rapid onset of a severe headache combined with the high fever — to seek immediate medical attention.

As always, it’s important to be aware but not to panic. The PHAC says that Canadians’ risk of developing West Nile virus is low — and the chances of developing the severe form are even lower.


Unfortunately, there is no vaccine for West Nile Virus, though researchers have a couple of possibilities in the works. In the meantime, it’s up to municipalities to tend to their own West Nile virus programs — and up to us as individuals to look after our own health.


For more information on West Nile virus, visit:

Fight the Bite
Health Canada: West Nile Virus
CDC West Nile Virus webpage

If you’re concerned about what’s going on in your area, look for information through your city’s website or health department. You can also find information through your provincial government’s website too. (If you’re living or travelling in the U.S, try your state’s health authority.)

Photo ©iStockphoto.com/ Alexander Zhiltsov

7 summer health risks
Protect against Lyme disease
10 symptoms not to ignore
The dog days of summer
Don’t get ill from your grill

Updated August 29 with new information.