Kent County health officials confirm Jamestown Canyon virus in West Michigan mosquitoes

A second mosquito-borne virus has been detected in West Michigan's Kent County, local health officials said. 

A mosquito surveillance program, which is routine for this time of year, has found Jamestown Canyon virus in mosquito samples collected from the Grand Rapids ZIP code of 49504.  

This is the second mosquito-borne virus detected in Kent County this year, with the West Nile virus confirmed in early June. It is also the first detection of Jamestown Canyon virus in that area since 2024. These are among the viruses that can spread through bites of infected mosquitoes. 

No human cases involving either virus have been identified at this time. 

"These early findings tell us that mosquito season isn't just starting — it's already well underway in our community," said Sara Simmonds, Director of Kent County's Environmental Health Division.  

Jamestown Canyon virus is found in much of the United States, but most cases are reported in the upper Midwest, according to the Centers for Disease Control. The virus was confirmed to be found in Southeast Michigan in July 2025. Many people who are infected experience no symptoms, but about half who do reach that point need hospital attention. The illness can result in symptoms ranging from fever, fatigue and headache to encephalitis or meningitis 

There is no vaccine or specific treatment for Jamestown Canyonk virus. Health officials say the best response is prevention with insect repellent, eliminate or refresh standing water such as from wading pools, and avoiding outdoor activity at dawn and dusk when mosquitoes are most active. 

The Kent County mosquito surveillance team will continue to monitor local conditions for mosquito-borne illnesses through late September.