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West Nile Virus

West Nile Basics

Most mosquitoes are simply annoying. But a small percentage can carry diseases like West Nile virus. Over the past few years, West Nile virus has been found in animals, birds, and humans in all continental states in the United States.

West Nile virus is transmitted to humans from the bite of mosquitoes that probably picked up the virus after feeding on infected birds. Pets and other animals can also become infected with West Nile virus. But you can't get the virus from touching (or other casual contact with) people or animals.

Most people are unlikely to become seriously ill from West Nile virus. In fact, someone who does get infected with West Nile virus may not even know it. That's because most people who do get the virus usually have few or no symptoms. A small number may have symptoms like those of the flu, such as fever and body aches. But they usually get better quickly.

The Centers for Disease Control and Prevention (CDC) believes that, after becoming infected, a person becomes immune and won't get sick from the virus again.

A small number of people (less than 1%) who are infected with West Nile virus do become seriously ill, though. They are usually people over the age of 50 who are at greater risk of developing a more severe form of the infection, such as encephalitis or meningitis.

These more serious forms of infection can cause long-term illness, brain damage, permanent disability, and — in rare cases — even death. Symptoms usually begin 3 to 14 days after a person has been infected.

Severe West Nile virus infection causes symptoms such as:

People who think they may have symptoms of West Nile virus should see a doctor right away. Diagnosing the infection early can help improve a person's chances of recovery.

Tips for Protecting Yourself

Although it's unlikely you'll be infected with West Nile virus, mosquito bites can still be an itchy nuisance. The CDC advises people to protect themselves from mosquito bites by using mosquito repellent, especially at times when mosquitoes are most active, such as at dusk and dawn.

The CDC recommends mosquito repellents that include one of the following ingredients:

Follow the manufacturer's instructions for applying the product.

Reapply mosquito repellant according to the directions on the product label. How often you have to apply more repellant all depends on how much DEET is in the product. Don't use a sunscreen that includes an insect repellent — sunscreen should be reapplied frequently but insect repellents should not.

The Environmental Protection Agency (EPA) offers the following tips for using insect repellents:

You can also take the following precautions to avoid mosquito bites and West Nile virus:

Reviewed by: Mary L. Gavin, MD
Date reviewed: August 2012

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Note: All information is for educational purposes only. For specific medical advice, diagnoses, and treatment, consult your doctor.
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