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Increase of Lyme disease cases can be linked to climate change
Pennsylvania has led the nation in confirmed cases of Lyme disease from 2012–2014, according to the most recent data available from the Centers for Disease Control and Prevention.

That’s not surprising given that Pennsylvania is a large state both in population and land that is 58 percent covered in forests, providing ideal habitat for blacklegged ticks—commonly called deer ticks and the carriers of Lyme disease in the northeastern, mid-Atlantic, and north-central United States.

In addition, deer ticks have been found in each of Pennsylvania’s 67 counties, and more than half of Pennsylvanians participate in outdoor recreation one or more times a week, increasing the chances of contracting Lyme disease.

Data from the Pennsylvania Department of Health shows there were 7,400 cases of Lyme disease in the commonwealth, compared with 5,900 during 2013, a 25 percent increase over the prior year.

However, the actual number of illnesses is most likely greater than what is reported to health officials due to the fact that many of the symptoms of tick-borne diseases are similar to those of other conditions, which complicates the diagnoses of Lyme disease.

Reported Lyme Dissease Cases in 1996 and 2013
Data source: CDC (Centers for Disease Control and Prevention). 2015. Lyme disease data and statitstics. For more information, visit U.S. EPA's "Climate Change Indicators in the United States."

So what are the reasons for this spread of deer ticks and Lyme disease? Science and studies are providing evidence that climate change is one of the factors contributing to the increase in the life span and range of ticks that can spread the disease.

According to the U.S. Environmental Protection Agency (EPA), the life cycle and prevalence of deer ticks are strongly influenced by temperature.

Climate change is increasing not only the range in which Lyme disease-carrying ticks can survive, but the amount of time in which ticks can feed.

For example, deer ticks are mostly active when temperatures are above 45°F, according to the EPA, and they thrive in areas with at least 85 percent humidity.

In addition, shorter winters also could extend the period when ticks are active each year, increasing the time that we can be exposed to contracting Lyme disease.

These climate patterns supporting the life cycle of deer ticks are happening in Pennsylvania in the form of higher temperatures and an increase in annual precipitation.

Since the early 20th century, the commonwealth has seen a temperature increase of more than 1.8° F. Winter temperatures have risen faster, at a rate of 1.3° F per decade from 1970 to 2000 in northeastern United States.

In addition, annual precipitation has increased about 10 percent during the past 100 years.

These changes in climate are predicted to increase, thereby continuing the risk of Lyme disease for Pennsylvanians in the future.

The commonwealth is projected to be as much as 5.4° F warmer by the middle of this century than it was at the end of last century. Additionally, annual precipitation is expected to increase by 8 percent.

But don’t just take our word. The correlation between climate change and the spread of Lyme disease is so significant, that the EPA monitors the spread of Lyme disease as an indicator of climate change in the U.S.

The majority of climate scientists agree that observed changes in climate patterns can be linked to rising levels of carbon dioxide and other greenhouse gases caused by human activities.

While climate change presents significant challenges, there is much DCNR can do to limit its effects. DCNR has made climate change a strategic priority and is working towards developing strategies to:

  • Manage our forests to sequester an increasing amount of carbon
  • Ensure that our public lands remain resilient
  • Help private landowners and communities reduce their carbon footprint and adapt to climate change

While we may not be able to limit the span of ticks that can spread Lyme disease, there are some tips you can follow from the Centers for Disease Control and Prevention to reduce your exposure to tick bites after spending time in the outdoors.


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July 20, 2016



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