West Nile virus (WNV) is an infection that is carried by birds and spread to people by the bite of an infected mosquito. Cases of West Nile virus occur during mosquito season, which starts in the summer and continues through fall. Anyone can get infected with West Nile virus, although people older than 50 years and those with weak immune systems are at greater risk of developing severe illness. Mild symptoms are flu-like and may include fever, headache, body aches, and sometimes a rash. Severe symptoms can include high fever, stiff neck, and swelling of the brain. There are no vaccines to prevent West Nile virus, nor are there treatments for it. You can reduce your risk of contracting the virus by using insect repellent and wearing long-sleeved shirts and long pants to prevent mosquito bites.