West Nile Virus
West Nile virus (WNV) is spread to people through the bite of infected mosquitoes. This disease is the leading cause of mosquito-borne illness across the United States, including in Connecticut. Several mosquito species in Connecticut can carry WNV. The symptoms of WNV infection can range from mild to severe. There is no vaccine to prevent or medicine to treat WNV virus infection. The best way to prevent getting sick from WNV is to prevent mosquito bites.
Data and Maps for West Nile Virus
Connecticut's West Nile Virus Response Plan (2025)
Information for Clinicians
National Surveillance Case Definition
Connecticut Provider Reporting Information
Connecticut Laboratory Reporting Information
WNV testing at the State Public Health Laboratory
State Public Health Laboratory Contacts – for additional information
Connecticut Agricultural Experiment Station
The Connecticut Agricultural Experiment Station conducts mosquito trapping and tests for viruses including West Nile virus during June to October each year.
Mosquito Trapping and Arbovirus Testing Program
Current Mosquito Testing Results
Past-Years Summaries of Mosquito Testing Results
Identification Guide to the Mosquitoes of Connecticut
Vector-borne Disease Symposium (2019)
Connecticut WNV Surveillance
In 2000, encephalitis was added to the state-wide reportable disease list, which included West Nile virus (WNV). WNV is a rare disease in Connecticut. Since 2000, an average of 8 cases (range 0 to 23 ) have been reported to the Connecticut Department of Public Health.
Connecticut Annual Infectious Diseases Statistics
Additional Resources
Connecticut Mosquito Management Program
Workplace Safety - Mosquito-Borne Diseases (NIOSH)
Updated 6/4/2025