Mosquito-borne Diseases
Mosquito-borne diseases are those spread by the bite of an infected mosquito. These diseases can be caused by viruses or parasites. Some mosquito species found in Connecticut are capable of spreading viruses that can cause disease in humans. Illness associated with these diseases ranges from mild to severe. Surveillance of mosquito-borne diseases in Connecticut is conducted to identify travel-associated diseases (acquired while outside of the state or the country) and diseases that can be spread by mosquitoes in the state. The following 10 mosquito-borne diseases are included in surveillance in Connecticut: California serogroup virus infections (e.g., Jamestown Canyon virus, LaCrosse virus), chikungunya, dengue, Eastern equine encephalitis (EEE), malaria, St. Louis encephalitis, Venezuelan equine encephalitis virus infection (VEE), West Nile virus (WNV) infection, yellow fever, and zika.
The two most consequential locally transmitted mosquito-borne diseases in Connecticut are WNV and EEE. Most human WNV cases occur in densely populated urban and suburban communities during August-September. Outbreaks of EEE occur sporadically; one human case was reported in Connecticut in 2013 and four human cases were reported in 2019. Most EEE virus activity occurs in the eastern part of the state during late July-September.
About Eastern Equine Encephalitis Virus
Actions Required and Control Measures
Reporting Requirements
Cases of Venezuelan equine encephalitis virus infection and yellow fever are reportable by phone on the day of diagnosis or suspicion (Category 1). Cases of California serogroup virus infection, chikungunya, dengue, EEE, malaria, St. Louis encephalitis virus infection, WNV infection, and zika virus infection are reportable within 12 hours of recognition or strong suspicion to both the Connecticut Department of Public Health (DPH) and the local health department (LHD) (Category 2). The director of any clinical laboratory must report laboratory evidence of infection with these pathogens.
To assure you have the most up-to-date information concerning reportable diseases, please visit the Reporting of Diseases, Emergency Illnesses, Health Conditions, and Laboratory Findings page.
National Surveillance Case Definitions:
Arboviral diseases (includes California serogroup virus diseases, chikungunya, EEE disease, St. Louis encephalitis virus disease, VEE disease, WNV disease)
Case Investigation
DPH Responsibility: For reported cases and laboratory findings, DPH staff determine whether the case meets public health surveillance criteria and if so, investigate whether the infection was likely acquired in Connecticut or if it is a travel-associated case. DPH staff also gather information from healthcare providers on disease symptoms and outcomes. For locally acquired cases, DPH staff interview patients to identify potential locations of exposure to mosquitoes.
Control Measures
Surveillance
Information from human, mosquito, and animal surveillance are reviewed in combination to understand mosquito-borne disease trends and risks in Connecticut. Surveillance data on human cases of illness reported to DPH are stored in CTEDSS. The Connecticut Agricultural Experiment Station (CAES) is responsible for trapping, identifying, and testing mosquitoes for arboviruses. Each year, CAES traps mosquitoes at more than 100 sites across the state during June–October. Mosquito testing results are updated weekly. DPH will notify LHDs via telephone of the first positive WNV or EEE mosquito pool for any new town or any new site within their jurisdiction. DPH will notify LHDs via email of subsequent positive WNV or EEE mosquito pools in their jurisdiction and inform them that updated mosquito testing results can be found on CAES’ website weekly.
Some mosquito-borne illnesses in animals are reportable to the Connecticut Department of Agriculture, including EEE and WNV diseases.
Preventing Illness
Preventing mosquito bites is the best way to prevent mosquito-borne illness. See CDC recommendations, communication materials, and information about mosquito control strategies to help prevent mosquito bites. The Connecticut Department of Energy and Environmental Protection (DEEP) recommends steps to control mosquitoes around the home. CDC also provides guidance on mosquito control after a hurricane or flood.
Other helpful resources include:
- Protection against mosquitoes using repellents – frequently asked questions
- Eastern Equine Encephalitis – frequently asked questions
Mosquito Management and Outbreaks
The Connecticut Mosquito Management Program is a collaborative effort involving five state agencies: DEEP, CAES, DPH, Department of Agriculture, and the University of Connecticut Department of Pathobiology and Veterinary Science. The program provides information about the species of mosquitoes found in Connecticut and guidance about how to protect yourself and your community from mosquitoes and mosquito-borne diseases.
When arboviral infections are detected in mammal-biting mosquitoes, animals, or humans, the CT Mosquito Management Program works collaboratively with local health departments to make the public aware of the risk of disease and protect public health through risk communication, reducing exposure opportunities (e.g., cancelling or rescheduling outdoor evening events, closing outdoor recreation areas), and mosquito spraying (if appropriate). Specific response plans are available for WNV and EEE.