BURLINGTON, Vt. — The Vermont Health Department has confirmed the state’s first human illness this year from West Nile virus spread by infected mosquitoes.

Officials said Friday that an Addison County resident has been diagnosed with neuroinvasive disease, which is a more serious form of the illness and affects the nervous system.

The virus has been found in mosquitoes in all counties in Vermont. The disease is spread to humans by the bite of an infected mosquito.

Officials say most people infected do not become ill and around 20 percent get flu-like symptoms. Officials say less than 1 percent develop the more severe illness.

There have been 12 confirmed human cases of West Nile virus in Vermont since 2003.