West Nile virus – Common questions

• West Nile virus (WNV) is a mosquito-borne virus that can cause West Nile Non-Neurological syndrome (formerly known as West Nile fever). Occasionally it can cause the more serious West Nile Neurological Syndrome. Until 1999, West Nile virus was only found in Africa, West and Central Asia, and the Middle East.

• It is thought to have been introduced into the New York City area in 1999 and was found in four eastern states by the end of 1999; how the virus entered is unknown.
• In 2000, the virus moved outward from the New York City metropolitan area to 12 states along the East Coast of the United States. In 2001, the virus was first detected in Ontario. It almost certainly entered Canada through an infected bird.

• Yes. For current and past surveillance results go to Evidence in Alberta .
• In 2005 and in 2009, Alberta Health and Wellness completed survey studies on the awareness of West Nile virus among Albertans. The reports present the results from the West Nile virus Seroprevalence Study during March through June 2004 and during March through June of 2007. Read the survey reports.
• Information on WNV in Canada can be found at the Public Health Agency of Canada.

• People become infected with West Nile virus primarily through the bite of a mosquito that carries the virus.
• Mosquitoes become infected with West Nile virus when they feed on infected birds. These infected mosquitoes then can transmit West Nile virus to humans and to other birds. Not all of the 43 species of mosquito present in Alberta will feed on humans, and a small number of those human-feeding species would actually carry the disease. Culex tarsalis, has been identified as the species of mosquito most likely to transmit the virus to humans.
• West Nile virus is not known to be spread by birds or other animals to people, or by direct person-to-person contact. Blood transfusion and organ transplantation have been confirmed as sources of human infection, but the risk of West Nile infection from blood and/or tissues remains very low. Read more on how Canadian Blood Services is protecting the blood supply against WNV.
• It is possible that a mother infected with West Nile virus can transfer the virus to an unborn fetus. This has rarely been associated with a spontaneous abortion or illness to the baby when born. It is important that a baby born to a mother who has WNV be examined by a doctor.
• It is also possible that the virus could be transferred when an individual is poked with a sharp medical instrument that contains infected blood.

• No. In Alberta and other areas where mosquitoes do carry the virus, only a small percentage of mosquito species will carry it.
• All Albertans, whether at home or traveling to infected areas, are encouraged to take steps to reduce their exposure to mosquito bites, including wearing long-sleeved shirts and trousers at night and at dawn, and using a mosquito repellent containing DEET or other approved ingredients.

• No. Illnesses related to mosquito bites are rare. However, you should see a doctor immediately if you develop symptoms such as high fever, confusion, muscle weakness or severe headaches. Patients with symptoms of West Nile Non-Neurological syndrome (formerly known as West Nile fever) may require prolonged bed rest, but are likely to recover completely and do not require any specific medication.

• While most people who become infected with West Nile virus will experience no symptoms, one in five will develop West Nile Non-Neurological syndrome (formerly known as West Nile fever). Symptoms can include fever, severe headache, body aches and possibly a rash. Very few individuals will experience the more severe symptoms of West Nile Neurological Syndrome.
• The neurological syndrome can include high fever, worsening headache and neck stiffness, stupor and disorientation, coma and tremors, occasional convulsions, paralysis, muscle weakness and numbness or difficulty moving. Long-term neurological effects have occurred in about 50 per cent of cases of West Nile Neurological Syndrome. In very rare cases, a West Nile virus infection can be fatal.

Most people who become infected with West Nile virus have no symptoms or may experience mild illness, such as a fever and headache, before fully recovering. One in five may develop West Nile Non-Neurological syndrome (formerly known as West Nile fever). Symptoms generally occur 2–14 days following the bite of an infected mosquito, and can include:

• Fever, chills;
• Severe headache;
• Body aches;
• Skin rash;
• Swollen glands;
• Nausea/vomiting.

In some individuals, West Nile virus can cause serious disease that affects the brain, either in the form of encephalitis or meningitis. This neurological syndrome can cause permanent neurological damage, and even be fatal. Symptoms related to the syndrome may include:

• High fever;
• Worsening headache and neck stiffness;
• Stupor and disorientation;
• Coma and tremors;
• Occasional convulsions;
• Paralysis;
• Muscle weakness;
• Numbness, difficulty moving.

• West Nile Neurological Syndrome is rare but can happen to individuals of any age. The risk of serious illness increases with age and for those with chronic medical conditions, but everyone can take simple steps to protect themselves.

• There is no specific treatment for West Nile Neurological Syndrome.
• More severe cases may require intensive supportive therapy – hospitalization, intravenous (IV) fluids, airway management, respiratory support (ventilator) if needed, prevention of secondary infections (pneumonia, urinary tract, etc.) and good nursing care. Recovered individuals can require physical or occupational therapy.

The best way to reduce the risk of infection is to reduce contact with mosquitoes. Severe disease is rare but can happen at any age. Everyone can take some simple precautions to reduce their risk of infection –

• Use a mosquito repellent containing DEET or other approved ingredients on exposed skin; apply it to clothing as well, because mosquitoes may bite through fabric.
• Wear long-sleeved shirts, pants and a hat when outdoors during peak mosquito biting periods.
• Place mosquito netting over infant carriers when outdoors.
• Repair window and door screens so that mosquitoes cannot get indoors.
• Adult females of some mosquito species will lay their eggs in shallow pools of warm, sunlit standing water. Take steps to prevent this on your property:
  • Regularly drain standing water from items like pool covers, saucers under flower pots, recycle bins, garbage cans etc.
  • Remove or cover unused items such as old tires that have a tendency to collect water.
  • Change the water in wading pools, bird baths, pet bowls and livestock watering tanks twice a week.
  • Cover rain barrels with screens.
  • Clean out eaves troughs regularly to prevent clogs that can trap water.
  • If you have an ornamental pond, consider getting fish that will eat mosquito larvae, or adding a fountain.

• West Nile virus is spread through birds and mosquitoes. It cannot be eliminated from these populations. The Government of Alberta's program includes human surveillance and a public education campaign focussing on how Albertans can reduce their risk of infection by reducing their exposure to mosquitoes, particularly in high risk areas.
• Read more on ways to reduce mosquito breeding sites on your property.

• The best way to prevent West Nile Neurological Syndrome or any other mosquito-borne illness is to take personal precautions to avoid mosquito bites, such as wearing an insect repellent containing DEET or other approved ingredient and long-sleeved shirts and trousers in the evening and at dawn.

• A horse vaccine against West Nile virus has been licensed for use in Canada, but to date no vaccine for West Nile virus has been approved for use in humans.

• To date, chronic infection with West Nile virus has not been reported. It is uncertain if humans develop long-lasting immunity after infection.

• The province has trained, authorized and guided municipalities in mosquito larvae control, especially in high and medium risk areas over the last few summers. These municipalities have the expertise and the necessary equipment to implement a larviciding program if they deem it a priority.
• Because of the limited effectiveness and potential environmental effects, the province does not recommend and does not fund spraying for adult mosquitoes. Spraying adult mosquitoes has a limited effect, and only for a short period of time. It only kills adult mosquitoes in the air at the time and it does not offer sustained protection. A strong wind can blow new mosquitoes into the sprayed area within hours.

• Of the 44 species of mosquitoes in Alberta, the Culex tarsalis is the species most likely to carry and transmit the virus from infected birds to people and horses.

• The breeding season of the Culex tarsalis runs from mid-June to September. The risk of contracting West Nile virus increases during this period and peaks during August.
• Culex tarsalis lay their eggs in shallow pools of warm, sunlit standing water.
• Read more on how to reduce mosquito breeding sites on your property.

• Birds are the main hosts for West Nile virus. Birds of the Corvid family (crows, magpies, ravens, blue jays and grey jays) are particularly susceptible. Bird survillance in previous years has provided a good understanding of the location and cycle of the virus.
• For more information on disease in birds visit the Alberta Sustainable Resource Development website.

• If you find a dead bird you can leave it alone, bury it, or in urban areas you can wrap the bird in plastic and put it out with the garbage.
• When dealing with any found dead wildlife, always wear leakproof rubber gloves or use two layers of a leakproof plastic bag inverted over your hand or a stick or shovel to move the bird into a plastic bag or container. Handle the carcas so that the beak and claws do not puncture the bag or gloves. Do not handle dead wildlife directly with your bare hands. After packaging the bird, wash your hands thoroughly with soap and water for at least 30 seconds.
• As in previous years, outbreak situations involving clusters of dead birds found in a small area and over a short time frame should be reported to a Fish and Wildlife office. While not likely to be West Nile virus, the cause of the mortality may be some other disease occurrence that should be investigated.

• Hunters, like all outdoor recreationists, should take precautions against being bitten by mosquitoes, which are common in wetland habitats and are active at dusk and dawn.
• There is no evidence to suggest, nor reason to believe, that the virus can transfer to anyone handling the carcass of hunter-killed waterfowl. Free-flying waterfowl are unlikely to contain sufficient virus to pass on an infection. Hunters and meat processors are encouraged to wear gloves or wash their hands thoroughly after handling any hunter-killed animal.