West Nile virus (WNV) is a mosquito-borne virus that can be transmitted to humans through the bite of an infected mosquito.
The main species that carries WNV in Saskatchewan is Culex tarsalis. The risk of becoming infected varies from year to year, depending on weather conditions and the number of infected Culex tarsalis mosquitoes.
When you are most at risk
You are most at risk in July, August and early September when Culex tarsalis mosquitoes are most active and present in higher numbers. If you spend a lot of time outside on the farm or worksite, at the cottage, camping, hiking, gardening or golfing, you are at higher risk of being bitten by mosquitoes.
Prevention is the first line of defence.
How to protect yourself
Minimize your exposure to mosquito bites:
- Use appropriate insect repellent when outdoors (see below);
- Cover up. Wear light coloured, loose fitting, long-sleeved tops and long pants when outdoors; and
- Reduce the amount of time spent outdoors between dusk and dawn. The peak mosquito hours are around dusk and dawn, but Culex mosquitoes, the mosquitoes that transmit WNV, will also bite during the night.
Reduce mosquito habitats:
- Culex mosquitoes lay their eggs on standing water. Even small amounts of water allowed to stand for a week or more may produce adult mosquitoes;
- Regularly clean and empty containers that can collect water such as bird baths and eaves troughs;
- Clear yards of old tires and other items that can collect water;
- Ensure rain barrels are covered with mosquito screening or are tightly sealed around the downspout; and
- Maintain door and window screens so they fit tightly and are free of holes.
Adult mosquitoes like to rest in long grass and sheltered shady areas. You can reduce your exposure to mosquitoes by regularly maintaining these areas around your home.
- Cut the grass around your home;
- Trim hedges and trees around doorways and outdoor seating areas (decks, patios, etc.); and
- Keep bushes, shrubs and lawns clear of overgrowth and debris.
Use DEET containing insect repellents on exposed skin. The concentration of DEET should be no higher than 30 per cent for adults and no higher than 10 per cent for children. Products with DEET are the most effective. Repellents with Icaridin and oil of lemon eucalyptus are also effective, however, these products should not be used on infants. Some repellents can also be applied to clothing, some restrictions apply.
ALWAYS read and follow the label directions for use for any repellent.
See Health Canada – Insect Repellents for more information
West Nile virus symptoms
Most people who have been infected with WNV experience no symptoms and do not get sick.
Approximately 20 per cent of people who become infected with WNV will develop a fever and other symptoms such as headache, body aches, joint pains, vomiting, diarrhea or rash. Most people with this type of illness recover completely. Fatigue and weakness can last for weeks or months.
Less than 1 per cent of people infected with WNV will develop a more serious illness such as encephalitis or meningitis (inflammation of the brain or surrounding tissues). This serious type of illness is called WNV neuroinvasive disease. Symptoms of WNV neuroinvasive disease can include headache, high fever, neck stiffness, disorientation, coma, tremors, seizures or paralysis.
Recovery from severe disease may take several weeks or months. Some of the neurologic effects may be permanent. About 10 per cent of people who develop neurologic infection due to WNV will die.
What you should do if you think you have WNV
- Contact your health professional or call HealthLine at 811.
- You do not need to seek medical attention for mild symptoms as they tend to improve on their own.
If you develop symptoms such as severe headaches, persistent high fever with stiffness, confusion, seizures or paralysis, seek medical attention immediately.
When do symptoms of WNV infection appear and how long they last
When WNV infection causes illness, symptoms usually begin 2 to 15 days following a bite from an infected mosquito. The length and extent of illness varies widely from person to person and depends on the severity of symptoms. Symptoms may last from a few days to up to several weeks, while severe neurological effects may continue for a longer period of time
There is no specific treatment, medication or cure for WNV disease. Serious cases are treated with supportive therapies to ease symptoms and maintain life. Supportive therapies include hospitalization, intravenous (IV) fluids, airway management, respiratory support and nursing care. Physical or occupational therapy may be needed to help with long-term effects.
Currently there is no human vaccine available to prevent WNV infection. There are a number of companies currently working on a vaccine but this is still in the development phase.
Long-term effects of WNV
Most people with mild symptoms recover completely within days to weeks. For people who get the rare neuroinvasive form of the disease, recovery may take several weeks to months. Unfortunately, some of the neurologic effects may be permanent.
Age is a significant predictor of recovery. Younger people are more likely to recover faster and completely, compared to those in the older age groups.
Who is most likely to get sick after being infected with WNV
People with weaker immune systems and people with chronic diseases are at greater risk for serious health effects. This may include people with cancer, diabetes, alcoholism, heart disease or people undergoing medical treatment (such as chemotherapy) that may weaken the immune system.
The risk of serious illness increases with age. However, anyone exposed to mosquitoes in an area where WNV has been detected is at risk for getting infected.
Immunity to WNV infection
Although West Nile virus has been circulating in Saskatchewan for several years, the majority of people have not been infected. In addition, the length of immunity after infection is unknown. Any immunity you may develop may decrease over time. Therefore, it is not wise to assume you are immune. People should still take precautions to prevent mosquito bites.
Animals and WNV infection
Horses bitten by infected mosquitoes may become seriously ill and die. There is a vaccine for horses. For more information see West Nile virus in horses.
Younger domestic birds have also been affected by WNV. Disease due to WNV has not been reported among cattle. Research has shown that weaning pigs may be susceptible to the virus. Cases of infected dogs and cats have been reported rarely. Dogs and cats seldom show any clinical symptoms of the disease. Cats may occasionally have a mild fever.
There are no vaccines to prevent or medications to treat WNV in pets. Insect repellents intended for humans are not recommended for use on animals. Contact your veterinarian if you have any questions regarding using a specific repellent on your individual pet.
Dead birds and small animals
Birds and animals die of many causes, including infectious diseases. Reasonable precautions should be taken before handling or disposing of dead birds and small animals.
No testing for WNV is performed on birds in Saskatchewan to inform the risk of WNV to the health of the public. Other indicators, such as mosquito surveillance, are used to determine the human health risk of WNV in the province.
Before handling or disposing of sick or dead wildlife, consult the information and handling instructions available from the Canadian Wildlife Health Cooperative (CWHC).