Many people who are bitten by an infected mosquito won't get sick—many others aren't as lucky. Since 1999, more than 30,000 people in the United States have been reported as getting sick with West Nile virus. Occasionally, an infected person may develop more severe disease such as "West Nile encephalitis," "West Nile meningitis" or "West Nile meningoencephalitis."
Encephalitis refers to an inflammation of the brain, meningitis is an inflammation of the membrane around the brain and the spinal cord, and meningoencephalitis refers to inflammation of the brain and the membrane surrounding it. Almost 13,000 of the individuals who have been reported as having West Nile virus since 1999 have been seriously ill, and more than 1,200 have died.
Another problem in some parts of the United States and many places in the tropics is dengue. The World Health Organization estimates there may be 50 – 100 million dengue infections in the world every year. Over 2.5 billion people are at risk of getting infected with dengue virus.
The reasons one person becomes severely ill from diseases mosquitoes carry and another doesn't are not entirely known, but why take a chance?
Control what you can. Improve your odds of avoiding mosquito spread viruses by using a repellent on exposed skin and clothes while outdoors.