As warmer weather sets in, Michigan is witnessing an uptick in mosquito-borne viruses, with recent tests confirming the presence of West Nile virus and Jamestown Canyon virus across various counties.
Health authorities in Washtenaw County have identified Jamestown Canyon virus in local mosquitoes, while the state has reported additional positive samples from counties including Bay, Kalamazoo, Ottawa, and Saginaw earlier this year.
Jamestown Canyon virus, primarily impacting individuals in the Upper Midwest and northeastern U.S., often peaks during this season. According to the Centers for Disease Control and Prevention, the majority of those infected exhibit no symptoms, though rare severe cases involving brain inflammation or meningitis can occur.
In Kent County, health officials have detected West Nile virus in three mosquito samples through ongoing surveillance efforts. This marks the first identification of the virus in the county for the 2025 season, according to a press release.
West Nile virus remains the leading mosquito-borne disease in the United States. While asymptomatic in most cases, approximately 20% of those infected experience mild, flu-like symptoms such as fever, headache, and body aches, Kent County health officials noted. In some instances, the virus can lead to serious neurological issues.
Thus far, the state has identified West Nile virus in a bird from Saginaw County and in mosquito pools from Bay, Macomb, and Midland counties, as detailed in a state report.
“These detections are a reminder that local mosquitoes are active and capable of spreading illness,” Brendan Earl, supervising sanitarian at the Kent County Health Department, emphasized. He advised residents to minimize risk by using insect repellent and removing standing water around homes.
According to Becky Reik, a zoonotic epidemiologist with the Michigan Department of Health and Human Services, the current situation aligns with expectations for a typical season. Monitoring efforts include surveillance data and predictive models that assess the likelihood of West Nile virus and Eastern Equine Encephalitis outbreaks.
Reik noted that warmer weather could alter predictions, stating, “If we get more hot weather, it’s going to start predicting more cases, so things could certainly change.” She highlighted the seriousness of human cases, which can result in severe illness or death.
While no human cases of Jamestown Canyon virus have been reported in Michigan this year, last year saw seven infections. Additionally, 31 residents tested positive for West Nile virus.
Positive mosquito tests don’t always correlate with human cases, Reik explained. “We don’t necessarily see the positive pools in places where we then have human cases that correspond,” she said. However, as cases often rise in August, taking precautions is advisable.
Reik added that significant West Nile virus outbreaks can occur even in years with low mosquito visibility: “Often the years that we have the worst West Nile virus outbreaks are years where people tell me they’re hardly seeing any mosquitoes.”
Health officials recommend using repellents containing 10%-35% DEET, avoiding outdoor activities at peak mosquito times, and maintaining property to prevent standing water. “Mosquito bites can give you much more serious diseases,” Reik warned, even if the immediate effects seem minor.
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