The Vermont Health Department says a number of mosquitoes trapped in Addison county last week were carriers of the West Nile virus.
West Nile virus is spread by the bite of an infected mosquito. It is spread from infected birds to mosquitoes and it can be passed to humans.
Every year the Health Department and Agency of Agriculture test dead birds and mosquitoes for the virus.
Only one out of five people who are infected with the virus experience symptoms and most symptoms are mild.
But West Nile virus can cause high fever and lead to the development of potentially fatal illness affecting the central nervous system, such as encephalitis or meningitis.
West Nile virus season peaks in late summer and runs through October.