How can I tell if it's West Nile?

The West Nile virus affects the central nervous system. About 80% of those who contract the virus may not show symptoms at all. Up to 20% of those infected may develop West Nile fever, which features mild flu-like symptoms. It is characterized by fever, headache, muscle aches, nausea, vomiting, and sometimes swollen lymph glands or a skin rash on the chest, stomach, and back. If symptoms develop, they generally occur within 2 to 15 days after infection.

Health Canada and the US Centers for Disease Control and Prevention estimate that fewer than 1% of those infected develop severe symptoms, and fewer than that experience life-threatening complications. People over 50, those with chronic health conditions (such as cancer, diabetes, alcoholism, or heart disease), and those with weakened immune systems are more likely to have serious health effects from West Nile virus.

About 1 out of every 150 infected people will develop severe illness. Severe symptoms include high fever, severe headache, muscle weakness, neck stiffness, confusion, tremors (shaking), numbness, sudden sensitivity to light, and convulsions (seizures). Infection with West Nile virus can result in encephalitis (an inflammation of the brain) or meningitis (an inflammation of the layers that cover the brain). West Nile virus can cause the brain or spinal cord to swell and block the flow of blood to the brain. This could lead to a coma, paralysis, or even death.

There is no cure for West Nile virus, and there are no medications or treatments that are specific to this condition. Although one may be available within the next few years, there is presently no human vaccine for the West Nile virus.

According to Dr. Andrew Simor, head of the department of microbiology at Sunnybrook and Women's College Hospital in Toronto, other infectious diseases (including influenza) pose a much greater risk to Canadians. For example, the flu is responsible for about 4,000 deaths in Canada each year.

While positive tests for mosquitoes carrying the virus are reported, most experts are urging Canadians to minimize their risk of mosquito bites. (See "Mosquitoes spreading disease" for tips.)

You should consult your doctor if you have the following symptoms:

  • fever
  • muscle weakness
  • severe headache
  • stiff neck
  • convulsions (seizures)
  • sudden sensitivity to light or an inability to perform routine tasks
  • extreme swelling or infection at the site of a mosquito bite

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