West Nile virus (WNV) is a disease spread by mosquitoes and is present in Simcoe Muskoka from spring to fall. Mosquitoes become infected when they feed on infected birds and can then spread the virus to people through their bites.

Most people infected with WNV have mild symptoms or no symptoms at all. In rare cases, the virus can cause serious illness, including meningitis, encephalitis (inflammation of the brain) and acute flaccid paralysis (loss of muscle function). Older adults, people with chronic health conditions such as heart disease or diabetes, and those with weakened immune systems are at greater risk of severe illness.

People can become infected at any time during mosquito season, but the risk is highest in summer and early fall.

Public health monitors WNV activity in the community to assess local risk.

Protect Yourself From Mosquito Bites

• You can reduce your risk of WNV by taking simple steps to prevent mosquito bites:

• Use an insect repellent approved for use in Canada and follow the label instructions.

• Wear light-coloured clothing, long sleeves, long pants, socks and a hat when mosquitoes are active.

• Remove standing water around your home to reduce mosquito breeding.

• Make sure window and door screens are in good condition to keep mosquitoes out.

Signs of Illness and When to Get Help

Most people who are bitten by an infected mosquito do not develop symptoms.

People who become ill usually experience mild symptoms three to 14 days after being bitten by an infected mosquito. Symptoms can include:

• Fever
• Headache
• Body aches
• Rash
• Nausea or vomiting

Symptoms may last several days.

Mild cases can be managed with over-the-counter medications. In rare cases, WNV can cause severe illness affecting the brain and nervous system, including encephalitis (inflammation of the brain), meningitis or acute flaccid paralysis (loss of muscle function). If you have symptoms and are concerned, contact your health-care provider.

There is currently no vaccine or specific antiviral treatment for WNV.

Reducing Mosquitoes Around Your Home

Removing standing water is one of the most effective ways to reduce mosquitoes around your home.

Mosquitoes lay their eggs in standing water. If water sits for more than seven days, eggs can develop into adult mosquitoes.

To help reduce mosquito numbers around your home:

• Empty standing water from buckets, flower pots, tires and other outdoor containers at least once a week.
• Change bird bath water weekly.
• Keep pools, spas and hot tubs covered and properly maintained.
• Make sure rain barrels have screens and gutters are clear.
• Remove water from outdoor furniture covers, boat covers and other items that collect water.

Surveillance and Mosquito Control in Simcoe Muskoka

Public health monitors mosquito populations and investigates reported human cases of WNV to help assess local risk and guide mosquito control activities.

Mosquito traps are placed throughout Simcoe Muskoka each week during the warmer months. Collected mosquitoes are identified and tested for WNV. Public health also monitors mosquito larvae in areas such as stormwater ponds, catch basins and roadside ditches to identify where mosquitoes are breeding.

Surveillance information helps determine whether mosquito control measures are needed. When appropriate, municipalities may apply larvicide to catch basins and other breeding sites. Larvicide targets mosquito larvae before they become adult mosquitoes, helping to reduce the number of mosquitoes that can spread WNV.

Larvicides are preferred over adult mosquito control because they are more targeted and have less impact on the environment. The Ministry of the Environment, Conservation and Parks has approved methoprene for use in catch basins and sewage lagoons. When used according to label directions, methoprene is not harmful to people.

Other Mosquito-Borne Diseases

In addition to WNV, mosquitoes can spread other diseases, including Eastern equine encephalitis virus (EEEV) and Zika virus.  

Eastern Equine Encephalitis Virus

Eastern equine encephalitis virus is a rare disease that can spread through the bite of an infected mosquito. Human cases are uncommon, but the virus has been detected in mosquitoes and horses in Ontario.

Zika Virus

Zika virus is mainly found in tropical and subtropical regions of the world. People are most at risk when travelling to areas where the virus is present. The mosquitoes that spread Zika virus are not commonly found in Ontario, so the risk of getting Zika virus locally is low. For more information about Zika virus, visit the Government of Canada website.

For people living in Ontario, WNV remains the most common mosquito-borne disease and the primary health concern.