Human Case of West Nile Virus in Halton

The Halton Region Health Department has received a preliminary report from the Public Health Ontario – Toronto Laboratory of a positive test for West Nile virus ( WNV ) infection in a Burlington female in her seventies, who subsequently died. Confirmatory testing for WNV infection is underway.

Halton Region’s mosquito surveillance program has found WNV in batches of mosquitoes for five consecutive weeks, indicating that the risk for human WNV illness continues to be elevated in Halton. The last WNV-associated death in Halton occurred in 2002, when there were 60 reported cases of human WNV illness. Since 2002, Halton has experienced four years with no human cases and four years with one to five cases per year.

“August and September are the months of highest WNV activity in mosquitoes and when human cases are most likely to occur,” said Dr. Bob Nosal, Medical Officer of Health for Halton Region. “While the risk of serious illness is low, it is prudent for all Halton residents, and especially older persons, to protect themselves from mosquito bites.”

About 80 per cent of persons infected with WNV do not become noticeably ill. About 20 per cent experience West Nile fever with chills, headache, muscle aches, nausea and vomiting, and sometimes a rash. Less than one per cent develop neurologic disease such as inflammation of the brain or paralysis of one or more arms or legs. Death is rare, occurring in less than one in a thousand infections. The risk for serious illness from WNV goes up with increasing age and in people with underlying illnesses.

Mosquitoes can transmit WNV to humans after becoming infected by feeding on birds carrying the virus. The following are steps that residents can take to protect themselves and their families from mosquitoes:

• Cover up. Wear light-coloured, long-sleeved shirts and pants with tightly-woven fabric.
• Avoid being outdoors from early evening to morning. This is when mosquitoes are most active and likely to bite, as well as at any time in shady, wooded areas.
• Ensure that window screens are well-fitted and in good repair.
• Reduce mosquito breeding sites around your home by getting rid of all water-filled containers and objects. Change the water in bird baths at least once per week.
• Use an approved insect repellent, such as one containing DEET.

Maps showing the locations of positive mosquito pools, as well as standing water sites that have had larvicide applied are available on the Health Department’s website at www.halton.ca/wnv.

To report standing water or for more information about West Nile virus, please dial 311 or call Halton Region at 905-825-6000, toll free 1-866-4HALTON (1-866-442-5866), TTY 905-827-9833 or e-mail wnv@halton.ca.

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