Ticks that carry Lyme disease are now found in half of all counties in the U.S., researchers from the Centers for Disease Control and Prevention revealed in a new study.
The symptoms of Lyme disease are sometimes mistaken for the flu. That's why knowing the areas where its vectors are found can help medical personnel make a more accurate diagnosis. However, information about the geographic distribution in the U.S. of the blacklegged tick (Ixodes scapularis) and the western blacklegged tick (Ixodes pacificus) - carriers of Lyme disease - is limited, with the latest published data dating back to 1998.
To determine the present distribution of these ticks, the researchers conducted a survey employing similar methods used in the 1998 study. They were able to specify counties that had established blacklegged tick populations and counties in which blacklegged ticks had been reported. They also identified counties that had no reports of the Lyme disease vectors.
Their results showed that the distribution of the blacklegged tick has increased from 30 percent of U.S. counties in 1998 to 45 percent. Additionally, the number of counties with established populations of such ticks has doubled since 1998.
The blacklegged tick's distribution expanded mostly in the northern U.S., while that of the western blacklegged tick rose from 3.4 percent to 3.6 percent overall.
"This study shows that the distribution of Lyme disease vectors has changed substantially over the last nearly two decades and highlights areas where risk for human exposure to ticks has changed during that time," lead researcher Rebecca Eisen said in a press release.
Eisen said the increased distribution of the ticks emphasizes the need "for continuing and enhancing vector surveillance efforts, particularly along the leading edges of range expansion."
Lyme disease is caused by a bacterium called Borrelia burgdorferi. Humans get infected when they are bitten by ticks carrying the bacteria. The disease can cause rash, fever, facial palsy and arthritis. If left untreated, complications like inflammation of the brain and spinal cord, heart palpitations and short-term memory problems can occur, according to the CDC.
The study was published online Jan. 18 in the Journal of Medical Entomology.
