What's West Nile Virus?

What exactly is the West Nile virus? And why is everyone buzzing about mosquitoes?

Even though it was discovered all the way back in 1937 in Africa, the West Nile virus probably didn't make its way to the United States until 1999. But since then, it has been a cause of concern all over the country during the summer months.

West Nile virus is caused by a bite from an infected mosquito that's already carrying the virus, but it's important to remember that not all mosquitoes are infected. In many parts of the United States, the risk of being bitten by an infected mosquito is greatest from July to early September. But in some parts of the country, mosquito bites can be a risk all year long.

Not everyone who gets bitten by an infected mosquito will get the virus. And although kids can get West Nile virus, it's rare for them to become very sick from it.

Symptoms of West Nile virus really depend on the person who becomes infected. Kids with normal immune systems (say: ih-myoon), the system of the body that fights off disease and infection, usually get just a mild "flu-like" illness and may not feel bad at all with the infection.

People over 50 years old and those with weakened immune systems due to HIV/AIDS, cancer, or organ transplants are most at risk for the infection.

West Nile Symptoms

Most of the time, symptoms of West Nile virus are similar to the flu and include:

  • fever
  • headache
  • neck and back stiffness
  • muscle ache
  • tiredness
  • joint pain
  • swollen glands
  • rash

In the most rare and extreme cases, West Nile virus can cause a condition called encephalitis (say: en-sef-uh-ly-tis), which is irritation and swelling of the brain.

West Nile virus is not spread from person to person. That means if your friend next door just got it, and you played together the day before, you won't get the virus. And though pets can get the virus, they can't spread it to people. The only way to get it is from the bite of an infected mosquito.

So, what's being done to stop the spread of West Nile virus? Health officials in each state do their best to find out where mosquitoes live and kill the eggs of mosquitoes that might carry the virus.

You can do your best to prevent coming in contact with West Nile virus. Here's what to do:

  • Wear insect repellent. Repellents that include one of these ingredients are best: DEET, lemon eucalyptus, or picaridin. Ask a parent to help you apply them.  
  • Playing outside at midday will help you avoid getting bitten because mosquitoes are most likely to be out during early morning or early evening.
  • When possible, wear socks, long sleeves, and long pants when you're playing outside.
  • Never play near standing water like creeks or wading pools (mosquitoes love to hang out there!).

Reviewed by: Steven Dowshen, MD
Date reviewed: August 2009

Kids Health

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

© 1995-2015 The Nemours Foundation/KidsHealth. All rights reserved.