Mapping Lyme: CDC Reveals Distribution of Lyme Disease-Causing Bacteria by County

U.S. distribution of Lyme disease-causing bacteria in ticks

A new study by CDC researchers maps the distribution of Lyme disease spirochetes, Borrelia burgdorferi sensu stricto and Borrelia mayonii, in host-seeking blacklegged ticks (Ixodes scapularis, in the eastern U.S.) or western blacklegged ticks (I. pacificus, in the western U.S.), relative to the previously reported distribution of these vector species. Ticks were considered present in a county if at least one tick was recorded. Counties where ticks have been reported without records of infection may be reported as such either if ticks were not tested or if the pathogen was not detected in tested samples. (Image originally published Fleshman et al 2021, Journal of Medical Entomology)

By Melissa Mayer

Excerpts from article (See link for article):

The team limited their search to data reported after 2000 that used advanced detection methods to identify spirochetes, since only B. burgdorferi s.s. or B. mayonii are confirmed to cause Lyme disease in the U.S.—and data that included related species could skew the map.

It turns out that, while vector ticks are distributed broadly, ticks carrying Lyme disease spirochetes have a more limited range. The ticks are established in 41 states (35 eastern and 6 western), but mapping revealed spirochetes in three-quarters of those eastern states and one-third of those western states. At a more local level, about 26 percent of counties where the ticks are established have records for Lyme disease spirochetes.

That news comes with some caveats, the researchers say. These numbers are a baseline and probably low. One reason is that surveillance efforts vary, with more monitoring happening in regions with more reports of Lyme disease cases. And, the team excluded records that didn’t adequately identify the spirochetes or list the county of collection.

Of course, Lyme disease isn’t the only tickborne illness in the country. “Tickborne diseases are becoming increasingly more common and widespread in the U.S.,” says Eisen. She points out that blacklegged ticks also carry pathogens that cause the relapsing fever Borrelia miyamotoi disease, anaplasmosis, babesiosis, one form of ehrlichiosis, and Powassan virus.

Reported County-Level Distribution of Lyme Disease Spirochetes, Borrelia burgdorferi sensu stricto and Borrelia mayonii (Spirochaetales: Spirochaetaceae), in Host-Seeking Ixodes scapularis and Ixodes pacificus Ticks (Acari: Ixodidae) in the Contiguous United States