Climate Change Impacts Infectious Diseases

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.
Your Questions Answered
What mosquito-borne diseases are found in Vermont?

There are currently two mosquito-borne diseases in Vermont:

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. Learn more about testing for mosquito-borne diseases in Vermont

Has climate change impacted mosquito-borne diseases that are already 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. 

Learn more about mosquito-borne diseases in Vermont

Has climate change impacted mosquito-borne diseases that are not currently in Vermont?

There are certain mosquito-borne diseases such as — 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.

Learn more about mosquito-borne diseases in Vermont

How can I prevent mosquito bites?
How can I reduce my risk for mosquito-borne diseases when traveling?
deer tick over an up arrow

Tickborne Diseases

The spread of tickborne diseases to humans, including Lyme disease and anaplasmosis, has been increasing in Vermont and many other northern states. While reports of Lyme disease in Vermont used to be rare in the early 1990s, it is now common to see over 400 confirmed cases reported in a year. Anaplasmosis has become an increasingly common tickborne disease in Vermont as well. "Be Tick Smart" and learn about tickborne diseases in Vermont and how to prevent tick bites.

Your Questions Answered
What ticks and tickborne diseases are found in Vermont?
What is the connection of tickborne diseases to climate change?

Warmer weather is one of several factors that have contributed to the spread of ticks in Vermont and the rise in tickborne diseases. Warmer winters make it easier for ticks to survive here year-round, while a longer warm season increases the length of time that ticks are active each year. Other factors contributing to an increase in tickborne diseases include better diagnosis and reporting by physicians, changes in forest cover, and changes in deer and small mammal populations that serve as hosts for tickborne diseases.

In areas where tickborne diseases are present, the likelihood of a person getting a tickborne disease depends on three factors:

  1. How many ticks are in the area

  2. How many of those ticks are infected with the pathogen

  3. How often people come into contact with those ticks.

To a varying degree, climate change can affect all three of these factors:

  • Ticks can only live in areas where the climate is suitable for them, having the right temperature and the right amount of moisture. Warming temperatures due to climate change, especially during the winter months, may make Vermont more hospitable to blacklegged ticks. Warmer winters can also help the survival of important hosts for ticks, like white-footed mice. This could result in tick populations increasing in areas where they are already present, and the introduction of ticks to areas that were not previously infested, such as colder, northern areas and areas at higher elevations.

  • Work done by our partners at Lyndon State College suggests that areas more densely populated with ticks in Vermont also tend to have higher rates of infection with Borrelia burgdorferi (the bacteria that causes Lyme disease) among these ticks. This suggests that in areas where blacklegged tick populations increase due to climate change, a greater proportion of these ticks may become infected with the bacteria.

  • Ticks are typically not active at temperatures below freezing. Warming temperatures due to climate change mean more days when ticks are active and looking for blood meals, which means a greater risk of ticks biting people.

Read the technical report on Climate Change, Lyme Disease and Other Tickborne Diseases

Which ticks can transmit diseases?

There are four types of ticks that can transmit diseases that currently exist in Vermont: the blacklegged tick (Ixodes scapularis), the American dog tick (Dermacentor variabilis), the woodchuck tick (Ixodes cookei), and the lone star tick (Amblyomma americanum). Nearly all (99%) of cases of tickborne diseases in Vermont are from blacklegged ticks, which are among the most commonly encountered ticks in the state. Learn about the different ticks found in Vermont

How can I prevent tick bites?

The best way to combat climate effects on tickborne diseases is to remember to take precautions against tick bites. Learn how to Be Tick Smart and prevent tick bites, and what you should do if you are bitten by a tick.

Can I monitor or report tickborne diseases?

Waterborne and Foodborne Diseases

icon with rain cloud and person holding their stomach

Heavy rains can wash contaminants into drinking, recreational and irrigation waters that can make people sick. Harmful contaminants include human and animal waste, industrial chemicals, oil and other fuels, pesticides and fertilizers. Heavy rains can also result in overflows of combined sewer systems, which are designed to treat both stormwater and wastewater at the same time. During heavy rains, there may not be enough capacity in the system, leading to the discharge of untreated or partially treated wastewater. Flooding can make all of these problems even worse.

Your Questions Answered
How does water contamination affect health?

Vermont averages over 500 reported cases of waterborne or foodborne illnesses each year. Reported illnesses are more likely during the warmest months and following heavy rains.

Beach closures are common following heavy rains, as sewage or animal waste can wash into surface waters and cause unsafe E. coli bacteria levels for up to 48 hours following a heavy rainfall. During Tropical Storm Irene, 30 public water systems experienced treatment system failures, many private wells were contaminated by flood waters, and over $10 million in damage occurred to crops and farmlands affected by flooding.

What waterborne and foodborne illnesses are reported in Vermont?

These are the waterborne and foodborne illnesses (food poisoning) that are reported in Vermont:

How will climate change affect waterborne and foodborne illnesses?

Days with very heavy rain (at least 1 inch or more) occur almost twice as often today as they did 50 years ago, and are expected to become even more frequent in the future. More frequent heavy rains combined with warmer water conditions are likely to increase the risk for waterborne and foodborne illnesses in the future.

How does my community monitor and protect surface waters after a heavy rain?

Here are some ways communities and organizations actively monitor and protect surface waters:

How can I keep my water and food safe after a flood or storm and during warm months?

Here are some tips to help you keep your water and food safe after a flood or storm and during warm months:

Can green infrastructure be used to better manage stormwater, reduce flooding, and improve water quality?

Green infrastructure is a way to manage the water from heavy rains and stormwater runoff that mimics the natural water cycle. Here are some resources for homeowners, businesses and municipalities:

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