Have itchy mosquito bites left you scratching your head about the risk of West Nile virus?

The virus, named after the district of Uganda where it was first identified in 1937, is spread primarily through mosquitoes in the late summer and early fall. The disease can disrupt the central nervous systems of humans, birds, and certain other animals, and some cases result in fatal encephalitis, a swelling of the brain.

West Nile first appeared in North America in 1999, and over 4,000 human cases have since been reported. There have been nearly 300 U.S. deaths associated with the virus, though most infections are so mild the symptoms go unnoticed. Scientists say the virus has taken root in the United States, so feed your head with the following facts before the next time the mosquitoes come to feed on you!

<<< Click on the images to the left to see how the virus spreads and learn about what it can do.

Source: The Centers for Disease Control and Prevention, U.S. Geological Survey, National Biological Information Infrastructure