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West Nile Virus FAQs

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West Nile Virus FAQs

FAQ overview

What is West Nile Virus?

West Nile Virus is a mosquito borne virus and is closely related to the viruses that cause Yellow fever, Dengue fever and St. Louis encephalitis.

How did West Nile Virus spread to Canada?

The virus was first detected in 1937, in the West Nile region of Uganda. After that outbreaks were found in Egypt, Israel, South Africa and in parts of Asia, Europe and North America. The first recorded outbreak in North America occurred in New York City in 1999.

It is not known how the virus spread to North America. One theory is that a migratory or imported bird, or an infected mosquito was transported to the area by accident.

How is West Nile Virus spread to humans?

Humans get West Nile Virus when a mosquito infected with the virus bites them. The mosquito gets West Nile Virus by feeding on the blood of an infected bird. Two weeks must pass before the mosquito is able to transfer the virus.

There is some evidence that mosquitoes can pass the virus to their offspring but that research is incomplete.

People can also get West Nile Virus through blood transfusion and organ donation but that risk is very low. There is some evidence that pregnant women can pass the virus to their unborn children and that the virus can also be passed through breast milk.

Laboratory workers who handle West Nile Virus specimens can contract the virus through cuts and needle punctures.

Who can get West Nile Virus?

Anyone can get West Nile Virus but most people will have little or no symptoms.
People with weak immune systems or chronic diseases are at greater risk of complications from West Nile Virus.

The risk of complications also increases with age, as anyone over the age of 50 has a naturally weaker immune system.

Newborns are also at risk because of an immature immune system.

Although cases of West Nile Virus in young children is rare, it is important for childcare providers to protect them from mosquito bites.

There is no evidence that you can get West Nile Virus through contact with a person that has the virus. The virus is not passed from animal (horses or pets) to human.

What are the symptoms of West Nile Virus?

Most people who get the virus never experience any symptoms. Some notice mild flu-like symptoms or rash and swollen lymph glands.

People with weak immune systems are at greater risk of complications from West Nile Virus and may experience the rapid onset of symptoms that include: severe headache, stiff neck, nausea, vomiting, high fever, difficulty swallowing, lack of coordination, paralysis, muscle weakness, loss of consciousness, drowsiness, or confusion.

These severe symptoms are associated with meningitis and encephalitis. Anyone who experiences the sudden onset of these symptoms should seek immediate medical attention.

How do doctors diagnose West Nile Virus?

Doctors make an initial diagnosis due to the symptoms associated with the virus.

Travel history is also considered. If a patient has travelled to an area populated with mosquitoes or an area where the virus has been confirmed, it increases the likelihood of West Nile Virus infection.

The virus is confirmed through two separate blood tests. The first test is taken at the onset of symptoms, the second three weeks later. Both tests must be positive for West Nile Virus antibodies before infection can be confirmed.

What treatments are available for West Nile Virus?

Currently only the symptoms of the disease are treated. Good nursing care to prevent secondary infections is important.

Is there a vaccine for West Nile Virus?

There is no licensed vaccine available for humans. The National Institute of Allergy and Infectious Disease in the United States is using a private company to test a prototype vaccine. The vaccine has shown promise in animal tests. Human tests are anticipated some time this year. Health Canada is monitoring the situation carefully. Keep in mind that a vaccine licensed in the United States is not automatically licensed in Canada.

There are two West Nile virus vaccines in Canada registered for use in horses only.

What are the long-term effects of West Nile Virus?

Since West Nile Virus is a fairly new disease the long-term health effects are not completely known. Some people with severe complications recover completely and others experience continuing health problems that include:

  • Muscle weakness, paralysis, fatigue and headache.
  • Confusion, depression, trouble concentrating and memory loss.
  • Difficulty completing daily tasks like preparing meals or shopping.
  • How can I protect myself from West Nile virus?

  • Avoid outdoor activities at dawn and dusk.
  • Wear loose-fitting, long-sleeved shirts and long pants made of tightly woven material.
  • Wear socks and shoes (never sandals), and a hat.
  • Wear light coloured clothing, as dark and bright colours attract mosquitoes.
  • Use insect repellents that contain DEET.
  • Remove all mosquito breeding sites from your property.
  • Make sure window and door screens fit securely and are free of rips and holes.
  • Where can I buy clothes that provide the best protection from mosquito bites?

    Clothes made of tightly woven materials provide the best protection. Any garment that is made of heavy knit cotton or water repellent nylon will protect you from mosquito bites. Clothes made of these materials can be purchased in any clothing store. Make sure you wear long sleeves, long pants, socks, shoes and a hat.

    When deep woods camping or hiking, you may want to invest in an insect barrier shirt, with a mesh hood that covers the face. There are many manufacturers of these shirts, and they are easily found at a store that sells camping and hunting equipment, or on the Internet. Simply type the words, insect barrier shirt, in the search area of the browser you are using.

    When do I need protection from mosquitoes?

    Mosquito season in Canada starts as early as the end of April and lasts until the first hard frost at the end of September or October.

    Mosquitoes are most active at dawn and dusk, however it is not uncommon to receive mosquito bites during the day in mosquito-populated areas.

    Can I use sunscreen and insect repellent with DEET at the same time?

    Combination repellent/sunscreen products are not recommended. If necessary, use the two products separately.

    If you use sunscreen and DEET repellents together, use a higher SPF sunscreen and apply more often.

    Which should I apply first, sunscreen or insect repellent with DEET?

    Apply sunscreen 30 minutes before sun exposure, and then apply DEET.

    Do all mosquitoes carry West Nile Virus?

    No. There are approximately 74 species of mosquitoes in Canada and the virus has been found in about 10 species.

    It is important to note that not all species of mosquitoes that carry the virus also bite humans.

    The Culex species is responsible for the spread of the virus in the Windsor-Essex area because they take their blood meals from both birds and humans.

    Only female mosquitoes bite, therefore they are the only ones that can pass the virus to humans.

    Less than 1% of mosquitoes in any given area are infected with West Nile Virus. However, since anyone can get West Nile Virus it is important for everyone to protect themselves from mosquito bites.

    Is the Health Unit going to use larvicide to reduce the mosquito population?

    The Health Unit is promoting personal protection and yard cleaning as the most effective ways to reduce the risk of West Nile Virus infection.

    The Health Unit will set mosquito traps in designated areas around Windsor-Essex County. The mosquitoes in these traps will be sent to Brock University in St. Catharines once a week for testing. Test results will also be sent to the Health Unit every week.

    A vector larviciding program has begun to reduce mosquito populations, under the authority of the Medical Officer of Health, under Ontario Regulation 199/03 and by permit approval of the Ministry of the Environment, in the following communities: Windsor, Essex, Tecumseh, Lakeshore, Leamington, LaSalle, Amherstburg, and Kingsville.

    Larviciding will take place to reduce populations of mosquito larvae, and to reduce the risk of the West Nile Virus to persons in Windsor-Essex County.

    The larvicide Aquabac 200G (Bti), PCP# 26863 will be applied to standing water that cannot be drained, and Altosid Pellets (PCP # 21809) to catch basins and Altosid Granules (PCP # 22676) to sewage lagoons. Only areas within 2 kilometres of urban communities will be treated.

    All larvicide will be applied by Ministry of the Environment licensed applicators or trained technicians.

    For more information, please contact the Windsor-Essex Health Unit at 258-2146 ext. 1450 or 1474.

    For more information on West Nile Virus, download the Health Unit's fact sheets or visit the Health Canada website.


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