West Nile Virus


In 1999, West Nile virus (WNV) was found in dead birds in coastal towns of Connecticut from Greenwich to Madison. The same year, it was also found in New York, New Jersey, and Maryland, marking the first time this virus was identified in North America. Within 3 years it spread across the country and remains an important cause of mosquito transmitted disease.


West Nile virus follows a complex life cycle in nature. Wild birds serve as the reservoir for WNV. The virus is transmitted among wild birds primarily by mosquitoes. Infected mosquitoes can also transmit the virus to other animals and people. While most birds do not become sick if infected, some do such as crows and blue jays. Among domestic animals, horses are the most susceptible to disease.


The State Mosquito Management Program, an interagency working group, was established to work with local governments in response to the threat of diseases that are transmitted by mosquitoes. The principal diseases of public health importance in Connecticut are eastern equine encephalitis virus (EEE) and WNV.


The Mosquito Management Program is based on an integrated pest management approach.  It aims to minimize the risk of disease transmission to people in an environmentally responsible way. The approach includes a combination of surveillance, education, mosquito control, and personal protection measures. Control recommendations reflect a graded response in proportion to the threat.


Surveillance activities currently include monitoring mosquitoes, domestic animals and poultry, and humans. To monitor for WNV infection in people, the Connecticut Department of Public Health provides laboratory testing of cerebrospinal fluid and blood from persons hospitalized with illnesses consistent with WNV infection.


Exposure to mosquitoes and the risk of acquiring WNV infection varies by season and geographic region. In Connecticut, the risk is highest during August and September. Among persons who travel to other states and internationally, the possibility of infection exists throughout the year. 


West Nile virus fact sheet


West Nile virus statistics


Vector-borne Disease Symposium  - Presentation recordings of symposium held at the Connecticut Agricultural Experiment Station on May 20, 2016.


Connecticut Epidemiologist Newsletters

Other helpful sites

To contact the Epidemiology and Emerging Infections Program, please call 860-509-7994.