Multiple mosquito samples infected with West Nile Virus have led state officials to raise Rhode Island’s risk level from “Medium” to “High,” according to a joint announcement Thursday from the Rhode Island Departments of Health (RIDOH) and Environmental Management (RIDEM).
The positive cases prompting the raised level of caution were found in Johnston, East Providence, and Cranston. The infected mosquitoes were found in samples collected on Aug. 18. Eighty-six mosquito pools were tested over the time period, totaling 461 mosquitoes in all. The three positive samples were from the genus Culex, which includes a wide variety of mosquito species that can carry West Nile, including the common house mosquito. The mosquitoes were tested at the state health department’s laboratory in Providence.
The state’s highest level of West Nile risk is “Critical,” which is one step above “High.”
East Providence kicked off this summer’s West Nile season when the first positive mosquito sample was collected there on July 21. The second positive sample came from Bristol on July 28.
So far, the largest collection of positive cases this year was found in the Aug. 12 batch of routine trapping and testing. Two positive samples hailed from East Providence, one came from Westerly, and another positive was found in West Greenwich. The East Providence mosquitoes were both Culex. The Westerly sample was Culiseta melanura, or the black-tailed mosquito, and the West Greenwich mosquito was Coquillettidia perturbans.
Mosquitoes in the latest samples tested negative for other illnesses, including Eastern Equine Encephalitis (EEE) and Jamestown Canyon Virus. West Nile remains the only mosquito-borne disease detected in Rhode Island this year.
West Nile Virus is the most common mosquito-borne illness in the U.S. While most people infected never develop symptoms, about one in five experience West Nile fever, which can bring on headaches, body aches, and other flu-like symptoms.
In rare cases, West Nile Virus can progress to serious neuroinvasive illnesses that involve encephalitis or meningitis. The U.S. Centers for Disease Control and Prevention (CDC) reports that about 10% of these severe infections are fatal, most often among people over age 60 or those who are immunocompromised.
As of Aug. 26, preliminary CDC data show 433 West Nile Virus cases across the nation, with neuroinvasive illness involved in 257 of those cases. The virus has been recorded in 34 states so far this year.
Because the national database uses data reported by counties, the CDC notes that West Nile cases are often undercounted. The data can skew toward overrepresenting more severe cases because people without neuroinvasive illness are less likely to be reported.
Between 1999 and 2024, the CDC documented 60,992 human cases of West Nile Virus nationwide, including 3,134 deaths.
Health officials advise Rhode Islanders to safeguard themselves against mosquito bites by using EPA-registered bug repellent and wearing long sleeves and pants, especially at dawn and dusk when mosquitoes are most active. Residents are also advised to remove standing water from yards to reduce breeding sites and to repair holes in window and door screens to keep mosquitoes out.
The Department of Health posts weekly mosquito testing updates on its website. More prevention tips are available at health.ri.gov/mosquito and dem.ri.gov/mosquito.
This story was originally published by the Rhode Island Current.
