The Expanding Reach of Lyme Disease

Lyme disease-carrying ticks found in half of US counties

/ Author:  / Reviewed by: Jennifer Gershman, PharmD, CPh

(RxWiki News) A few decades ago, contracting Lyme disease in the US may have seemed like a stroke of bad luck. But today, the risk may be a whole lot greater.

A new study found that the two types of ticks responsible for the spread of Lyme disease have increased their range in the US. Researchers say both the blacklegged tick and the Western blacklegged tick have boosted their turf to include nearly half of all US counties.

Nearly 30,000 new cases of Lyme disease were reported to the Centers for Disease Control and Prevention (CDC) in 2014.

Lyme disease is a bacterial infection transmitted to humans through the bite of infected ticks. Symptoms include fever, headache, fatigue and rash.

According to the CDC, recognizing the symptoms of Lyme disease is crucial, as patients who receive appropriate antibiotics in the early stages of infection can recover completely. If left untreated, Lyme disease can spread to the joints, heart and nervous system.

Rebecca Eisen, PhD, is a research biologist at the CDC. Upon realizing that the last comprehensive survey of blacklegged tick distribution in the US was nearly two decades ago in 1998, she assembled a research team to track the ticks’ current distribution.

Dr. Eisen and team used surveillance records to classify the tick populations of each US county as either established, reported (one or more reports) or containing no record. A population was considered established if six individual ticks had been identified in a single collection period of one year.

Researchers found that blacklegged tick populations were reported in more than 45 percent of US counties — a 15 percent increase since 1998. The number of established counties for the blacklegged tick also doubled during that time.

While the blacklegged tick expanded its range significantly in recent years, the Western blacklegged tick only increased its range from 3.4 to 3.6 percent of US counties since 1998.

"The observed range expansion of the ticks highlights a need for continuing and enhancing vector surveillance efforts, particularly along the leading edges of range expansion," Dr. Eisen said in a press release.

This study was published Jan. 18 in the Journal of Medical Entomology.

Information on funding sources and conflicts of interest was not available at the time of publication.

Review Date: 
January 14, 2016
Last Updated:
January 18, 2016