Lyme disease—named after Lyme, CT, where the disease was first recognized in a group of children and adults in the 1970s—has ever since been associated with the Northeast. Now comes news from the Centers for Disease Control and Prevention (CDC) that the blacklegged ticks that cause Lyme disease are currently found in almost half of all U.S. counties, across 43 states.
Even more surprising, a newly identified strain of Lyme disease has been found in several states in the Midwest.
The new findings on the spread of the blacklegged ticks were reported in 2016 in the Journal of Medical Entomology. The authors noted that since 1991, when standardized surveillance and reporting began, Lyme disease cases have risen steadily in number and in geographical distribution in the United States.
To accurately determine the most recent changes in tick distribution, the investigators used surveillance methods similar to those used in 1998—the last time a comprehensive survey was published.
They found that the blacklegged tick has been reported in 1,531 of the 3,110 counties in the continental United States. This means that the ticks have spread beyond the eastern states and are now in 49 percent of counties across the country—a 45 percent increase since 1998.
The geographic spread appears to have occurred predominantly in the northern states. In addition to the Northeast, Lyme disease is prevalent in Pennsylvania and much of the Midwest region, including Wisconsin, Illinois, and Indiana.
Lyme disease is also prevalent in the U.S. Northwest. However, tick populations in the southern states have remained fairly stable.
In 2016, researchers at the CDC and the Mayo Clinic discovered that some blacklegged ticks are carrying a new species of bacteria (Borrelia mayonii) that also causes Lyme disease in humans. Until this discovery, Borrelia burgdorferi was the only bacterial species believed to cause Lyme disease in North America.
According to a report in the May 2016 issue of The Lancet Infectious Diseases, the symptoms caused by B. mayonii are similar, but not identical, to those caused by B. burgdorferi.
Notably, B. mayonii is associated with nausea and vomiting, diffuse rashes (rather than a single so-called bull’s-eye rash), and a higher concentration of bacteria in the blood. However, both types of infection cause fever, headache, rash, and neck pain in the first days after exposure and arthritis in later stages of infection.
The newly recognized species was discovered when blood samples, obtained between 2012 and 2014 from six residents of Minnesota, Wisconsin, and North Dakota who were suspected of having Lyme disease, were found to contain bacteria that were genetically distinct from B. burgdorferi.
Currently, B. mayonii has been found only in the upper Midwest. The good news is that the new strain can be identified with currently used diagnostic tests and can be treated effectively with antibiotics commonly used to treat Lyme disease caused by B. burgdorferi.
Tips for prevention
To protect yourself from tick bites, the CDC offers this advice:
• Cover exposed skin (and tuck your pant legs into your socks).
• Use an insect repellent containing 20 percent or more DEET (N,N-diethyl-m-toluamide).
• Perform daily checks of your entire body; that includes under the arms, in an around the ears, inside the belly button, the back of the knees, in and around all head and body hair, between the legs, and around the waist.
• Don’t forget to check your clothing and your pets for ticks.
If you find an attached tick, remove it with fine-tipped tweezers right away, and be alert for Lyme disease symptoms. If you experience symptoms, contact your doctor so treatment can be initiated promptly.
Learn how to prevent rashes and other summer illnesses.