Fact Sheets : West Nile Virus

The West Nile virus belongs to a family of viruses called Flaviviridae and was first isolated(1937) in the West Nile province of Uganda. The first West Nile virus infection in North America occurred in the New York City area in the summer of 1999. During 2002, more than 4,000 people in North America became ill with West Nile virus.

How do people get infected with West Nile virus?

Most people infected with West Nile virus got it from the bite of an infected mosquito. A mosquito becomes infected when it feeds on a bird that is infected with the virus. The mosquito can then pass the virus to people and animals by biting them. There have been cases in Canada and the United States of West Nile virus being spread through blood transfusions and organ transplants. However, there is no evidence to suggest that people can get West Nile virus by touching or kissing someone who is infected, or from being around a health care worker who has treated an infected person. Also, there is no evidence that the virus can pass directly from infected animals(horses, pets, etc.)to people.

Who is most at risk?

Many people infected with West Nile virus have mild symptoms, or no symptoms at all. Although anybody can have serious health effects, it is people with weaker immune systems that are at greater risk for serious complications. This higher risk group include: People over the age of 40, people with chronic diseases and individuals that require medical treatment that may weaken the immune system. Although individuals with weaker immune systems are at greater risk, West Nile virus can cause severe complications for people of any age and any health status. This is why it is so important to reduce the risk of getting bitten by mosquitoes.

Symptoms of West Nile virus infection

Symptoms usually appear within two to 15 days. The symptoms vary from person to person. Symptoms of Mild disease include: flu-like symptoms, fever, headache/body aches and a rash.

Persons with weaker immune systems or chronic disease, are at greater risk of developing more serious complications, including meningitis(infection of the covering of the brain) and encephalitis(infection of the brain). Tragically, these conditions can be fatal. Symptoms of more severe disease include: severe headache, high fever, stiff neck, nausea/vomiting, sleepiness and/or confusion , loss of consciousness and/or coordination, and muscle weakness and paralysis.

Is there a treatment for West Nile virus infection?

Unfortunately, as with most viruses, there is no specific treatment or medication for West Nile virus. Currently, there is no vaccine available to protect against West Nile virus, although there is a lot of research going on in this area.

How is West Nile virus infection confirmed?

If a doctor suspects that a person may have West Nile virus, based on the history of symptoms, especially in an area where it is known that there is West Nile virus, there are specific blood tests which confirm the infection.

The best way to reduce the risk of infection is to try to prevent mosquito bites.