Risk of Tick-Borne Lyme Disease Spreading to New Areas

The number of counties with a high occurrence of Lyme disease has more than tripled in recent decades. Find out which areas are at increased risk.

The number of counties with a high occurrence of Lyme disease has more than tripled in recent decades, according to research by the U.S. Centers for Disease Control and Prevention.

Between 2008 and 2012, 260 counties were considered to have a high incidence of Lyme disease by the CDC. That’s up from just 69 counties between 1993 and 1997.

Titled “Geographic Distribution and Expansion of Human Lyme Disease, United States,” the study was released online Wednesday and will be published in the journal Emerging Infectious Diseases next month.

This CDC illustration from the study shows the increase in the number of high-incidence counties — as well as the disease’s spread into additional states — since 1993:

United States counties with high incidence of Lyme disease by the period when they first met the designated high-incidence criteria, 1993–2012 / U.S. Centers for Disease Control and Prevention

Lyme disease is caused by a bacterium (called Borrelia burgdorferi) that is primarily carried and transmitted by deer ticks after they bite and attach themselves to a host such as a human, according to the Mayo Clinic.

It is the most common tick-borne illness in both North America and Europe, according to Mayo.

Early symptoms can include a rash or flu-like symptoms. Later on, joint pain and neurological symptoms may appear, including:

  • Inflammation of the membranes surrounding the brain (meningitis)
  • Temporary paralysis of one side of the face (Bell’s palsy)
  • Numbness or weakness in limbs and impaired muscle movement

People who live in or spend time in grassy and heavily wooded areas where deer ticks thrive are at higher risk for Lyme disease, according to Mayo.

Although Lyme disease cases are concentrated in select Midwestern and Northeastern states, CDC statistics show that cases of the illness are reported across the country every year.

The CDC study states that human behavior and changing landscape characteristics have influenced the spreading risk for Lyme disease:

Geographic expansion of high-risk areas may occur because of changes in conditions that favor tick survival or because of geographic dispersal of infected ticks by birds and deer to areas where other necessary components already exist to support ongoing transmission. Our results show that geographic expansion of high-risk areas is ongoing, emphasizing the need to identify broadly implementable and effective public health interventions to prevent human Lyme disease.

To learn more about keeping Lyme disease at bay, check out “How to Ward Off Ticks and 5 Other Threats to Summer Fun.”

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Stacy Johnson

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