The Windsor-Essex County Health Unit has found West Nile virus in a local mosquito pool.
The health unit tested 42 pools.
The positive test for one of them is the first sign of the virus in the region this year.
A mosquito pool is a group of mosquitos gathered for testing.
To date, no human cases of the disease have been found in Windsor-Essex.
The health unit reminds people to protect themselves by using insect repellent and wearing light clothing outdoors.