The virus is spread when a person is bitten by a mosquito carrying the virus. Rarely, West Nile virus also has been spread through blood transfusions.
About 80 percent of people who contract the virus never become sick. Of those who become sick, most will have a mild illness called West Nile fever that lasts two to 10 days.
Common symptoms of West Nile fever include headache, fever and tiredness, according to the state Health Department. Some people might also develop a rash.
In some cases, West Nile virus can cause severe neurological diseases such as meningitis, or swollen membranes in the brain and spinal cord; paralysis, or loss of muscle function; or encephalitis, which is swelling and inflammation of the brain.
Public health officials urge residents to use mosquito repellent while outside and clear homes of standing water, which can serve as breeding grounds for mosquitoes.