Climate Change and Mosquito-Borne Diseases

Mosquitoes can be a major annoyance during warmer months in Vermont and can occasionally transmit serious diseases. West Nile Virus (WNV) has been detected in every county of Vermont and typically infects three or fewer Vermonters each year. Eastern Equine Encephalitis (EEE) has also been detected in Vermont and caused two deaths in Rutland County in 2011.

Climate change is expected to affect mosquito-borne diseases in two ways:

  1. Increase the risk for people to get diseases that are already here.
  2. Bring in mosquito species that did not previously exist here, increasing the possibility for other mosquito-borne diseases to spread in Vermont.
Climate change impacts on mosquito-borne diseases are already present in Vermont.

Both mosquitoes and bird hosts are required for both of these diseases to persist, and climate change can affect populations of both. For example, warming temperatures can lengthen the season in which mosquitoes are out and biting, and accelerate the mosquito life cycle. This can mean more frequent contact between mosquitoes and their hosts, which can facilitate the spread of diseases. Changing precipitation patterns, with longer periods between rains but heavier rain events, may affect the amount of standing water that mosquitoes have to breed in. Climate change may also alter bird migration patterns, which can affect the transmission of diseases like WNV and EEE, although it is unknown as to what extent these changes affect disease transmission. The life cycle of these diseases is complex, so it is unclear exactly how climate change will affect them in the future. 

Climate change impacts on mosquito-borne diseases not currently in Vermont.

There are certain mosquito-borne diseases such as the Zika, dengue, and chikungunya viruses that are transmitted by mosquito species that are not currently known to have established populations in Vermont. These diseases are traditionally associated with tropical and sub-tropical regions far to the south of Vermont. Unlike WNV and EEE, these diseases are transmitted primarily from person to person by the bite of infected mosquitoes, rather than from birds to people by mosquitoes. The mosquitoes that transmit these viruses (Aedes aegypti and Aedes albopictus) are not known to currently exist in Vermont, although Aedes albopictus is established in more southern areas of the Northeast. While climate change may influence the northern expansion of these mosquitoes, there are many other factors that have prevented the spread of these tropical diseases in the United States, including effective mosquito control.

Prevent Mosquito Bites
Reduce Your Risks When Traveling
Learn more about mosquito-borne diseases in Vermont and how Vermont keeps track of them.

The Vermont Agency of Agriculture, Food and Markets, working with the Health Department , collects and tests mosquitoes across the state for WNV and EEE every summer. For more information on these efforts, please visit: