West Nile Virus
In areas where the virus is circulating, very few mosquitoes are infected with the West Nile virus. Even if the mosquito is infected, not everyone who gets bitten by an infected mosquito actually develops West Nile virus symptoms. Even if someone does develop symptoms, they are usually mild. In fact, less than 1 percent of people who get bitten and become infected will get severely ill. The chances you will become severely ill from a single mosquito bite are extremely small.
However, there are certain factors that increase a person's chance of developing West Nile virus disease. These factors are known as West Nile virus risk factors. They include:
- Living in areas where virus activity has been identified
- Being over 50 years of age.
The easiest and best way to avoid this virus is to prevent mosquito bites.
(Click West Nile Virus Prevention for strategies that can help prevent a West Nile virus infection.)
People typically develop symptoms between 3 and 14 days after they are bitten by an infected mosquito.
When a person becomes infected, his or her symptoms can vary. Approximately 80 percent of people (about 4 out of 5) who are infected with West Nile virus will not show any symptoms at all. Up to 20 percent of the people who become infected have flu-like symptoms (known as West Nile fever). About 1 in 150 people infected with West Nile virus will develop severe signs and symptoms of West Nile virus (known as neuroinvasive disease, West Nile encephalitis, meningitis, or West Nile poliomyelitis).