What is West Nile Virus?
West Nile is a virus that is carried and spread by mosquitoes and can cause fatal inflammation of brain (encephalitis) or the membranes covering the brain or spinal cord (meningitis) in more than 100 bird species, and nine mammals, including humans, horses and gorillas. It is closely related to St. Louis encephalitis virus, found in North America. 
There is currently no vaccine against West Nile virus encephalitis.
West Nile virus was discovered in the West Nile area of Uganda in 1937, then spread to Mediterranean and temperate parts of Europe. In 1960, it was observed in horses in Egypt and France. Between the 1950s and 1999, there were sporadic epidemics in Israel, South Africa, Romania and in Russia.
How is it spread?
The Culex pipiens or common household mosquito spreads the virus when it feeds on a blood meal from infected birds. Scientists believe that the most likely "reservoir" for the virus in North America is the common sparrow, which can tolerate the infection. Among birds, the virus has had the greatest impact among crows. In 1999, in the New York area, the crow population crashed by about 90 per cent in a few months.
Ten days to two weeks after the initial blood meal, the West Nile virus reaches the mosquito's salivary glands and can then be transmitted to birds, animals or humans. Since 1999, the virus has been found in wild birds, humans and horses across the United States and Canada.
There is no evidence that West Nile virus can be spread directly from human to human. Nor is there evidence that a human can contract the West Nile virus by handling infected birds. Scientists believe the human immune system prevents the virus from multiplying in large numbers. That prevents humans from transmitting the virus to mosquitoes.
What are the symptoms?
Symptoms are usually mild and include fever, headache, body aches, sometimes skin rash and swollen lymph glands. Severe infection is marked by headache, high fever, neck stiffness, stupor, disorientation, with coma, tremors, convulsions, paralysis and occasionally death.Currently (2003) doctors estimate that 80% of humans infected have no symptoms; 20% have mild symptoms; and 0.5% have severe symptoms.
Anyone with those symptoms should seek medical attention as soon as possible.
If illness occurs, it usually happens within five to 15 days of being bitten by an infected mosquito.
What can you do to prevent it?
Avoid mosquito bites to avoid infection. To avoid mosquito bites:
- Use insect repellents containing 10 per cent or less DEET (N, N-diethyl-methyl-meta-toluamide) for children and no more than 30 per cent DEET for adults.
- When possible, wear long-sleeved clothes and long pants treated with repellents containing permethrin or DEET since mosquitoes may bite through thin clothing. Do not apply repellents containing permethrin directly to exposed skin. If you spray your clothing, there is no need to spray repellent containing DEET on the skin under your clothing.
- Consider staying indoors at dawn, dusk, and in the early evening, which are peak mosquito biting times.
- Wear light coloured clothing as it is less attractive to mosquitos.
- Avoid eating substances known to attract mosquitos such as bananas. Citrus fruits are okay and are reported to have some slight repellant effect.
- If practical, work outdoors when it is cooler and there is brisk air movement or when there is strong sunlight. Mosquitos are less active in these weather conditions.
- Reapply repellant every hour or more often if perspiration is high.
- Keep repellant away from eyes and mouth and to help prevent eye and mouth contact, do not apply to palms of hands and fingers. Rinse your hands after applying repellant.
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