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New CDC Study Details County-Level Distribution of Seven Diseases Spread by Blacklegged Ticks

blacklegged tick (Ixodes scapularis)

As surveillance for ticks and the disease-causing germs they spread improves, so does Americans’ access to knowledge about where the risk of tickborne disease is greatest. Experts at the U.S. Centers for Disease Control and Prevention’s Division of Vector-Borne Diseases have assembled new surveillance data into a report thatoffers up-to-date county-level maps of both where blacklegged ticks (Ixodes scapularis), shown here, are prevalent and where they’ve been found infected with any of seven different disease-causing germs, or pathogens. (Photo by Susan Ellis,

As surveillance for ticks and the disease-causing germs they spread improves, so does Americans’ access to knowledge about where the risk of tickborne disease is greatest.

“The more we look for ticks and tickborne pathogens, the more we find—and the more information we have to help protect people from the diseases ticks spread.” says Erik Foster, MS, BCE., medical entomologist in the U.S. Centers for Disease Control and Prevention’s Division of Vector-Borne Diseases. Foster and CDC colleagues have assembled that surveillance data into a new report, published May 18 in the Entomological Society of America’s Journal of Medical Entomology. The report offers up-to-date county-level maps of both where blacklegged ticks are prevalent and where they’ve been found infected with any of seven different disease-causing germs, or pathogens.

Of all diseases transmitted to humans by insects and related arthropods, those spread by ticks account for more than 75% of infections reported every year. The maps provided in the new CDC study are important for raising awareness both among the public and healthcare providers about the tickborne diseases present in their communities and the signs and symptoms to look for in patients. Making that possible is CDC’s growing national tick and tickborne pathogen surveillance program, launched in 2018.

Previously, knowledge of the distribution of ticks and tickborne human pathogens was limited to data shared by local public health agencies or in academic research.

“Collection efforts were not standardized, and data were often lost because there was no national repository for such information,” Foster says.

Since 2018, CDC has established a nationwide program that guides local agencies and academic partners on tick surveillance and pathogen testing and gathers all that data in one place.

“This effort is filling gaps in our knowledge by highlighting the presence of ticks and tickborne pathogens where they were previously under-reported or where they are emerging,” says Foster.

For their new study, CDC researchers combined nationwide tick surveillance records from 2004 through 2021 with additional data on pathogen testing in blacklegged ticks from published research studies and from archives on public health department websites.

The results offer the most current picture of the geographic range of seven significant human disease-causing pathogens known to be transmitted by blacklegged ticks (Ixodes scapularis) and western blacklegged ticks (Ixodes pacificus). Most widely reported is the bacteria Borrelia burgdorferi, which causes Lyme disease, found in 476 counties across 29 states and the District of Columbia.

Pathogen Disease States Counties
Borrelia burgdorferi Lyme disease 30* 476
Borrelia miyamotoi Hard tick relapsing fever 25* 271
Anaplasma phagocytophilum Anaplasmosis 24* 291
Babesia microti Babesiosis 17 154
Powassan virus Powassan virus disease 6 55
Borrelia mayonii Lyme disease 4 12
Ehrlichia muris eauclairensis Ehrlichiosis 2 11

*total includes District of Columbia

In all cases, the reported distribution of pathogens is significantly narrower than the known range of the blacklegged ticks that spread them. But Foster and colleagues caution, however, that the true presence of the pathogens is likely much wider than detected.

“These maps display county-level records of host-seeking ticks found infected with tickborne pathogens using rigorous laboratory standards,” Foster says.

In areas where pathogens aren’t detected, “this does not mean that tickborne pathogens are not present, just that records meeting collection and laboratory standards have not been published or documented by CDC in host-seeking ticks.”

The national tick surveillance program is an ongoing effort and CDC hopes to continue to update the maps to provide current and accurate information to the public and to healthcare providers.

Thus, while surveillance and detection of tickborne disease pathogens continues to improve, this new CDC research also indicates where further progress should be made. And, wherever ticks are present, public awareness is critical.

“It’s important for the public to understand that any exposure to ticks may pose a risk and that tick bite prevention is the best way to lower that risk,” says Foster. “Anyone who has symptoms of illness after a tick bite should see their healthcare provider and report tick exposure promptly.”


  1. Lyme is present in all 50 states. Ticks have no borders. The lack of this common knowledge, while pushing this info with a tiny asterisk has harmed countless people. Reporting is absolutely flawed. Doctors are not testing because they ignorantly believe that these diseases do not exist, thus the CDC keeps pushing that there are no records. And round and round we go, while people are severely ill from multiple tick borne diseases across the country and the world.

    • Thank you… 100% agree with this statement. I am almost sure I have lyme an no doctor will take me seriously… So I live with it it’s difficult. Clearly something is wrong… It’s a silent population control possibly… Idk. But how can they not exist? Real doctors don’t exist is my opinion. I just need the prescription pad I don’t need them. It’s rediculous how bad you are treated. I know my body an if I say I know smthn is weird or different I know that it is. I can’t wait till I get it figured out cause I will get my compensation finally… I won’t even see a doctor anymore an now 8 or more years later I can actually show them but they made me hate them so much I don’t go… It’s a shame. Hypocritical oath means nothing anymore. It’s all about the meds an money. Not the true underlying issues. It’s a joke an lies and not even reality anymore. Sad. Very sad. Thank you for ur comment. I appreciate it.

    • Agree. We had similar response from a highly respected Dr in Atlanta regarding RMSF. My wife had all the symptoms including the ring around the bite. I had printed documentation from WebMD and others to take with us on our appr. She stated several times RMSF doesn’t exist around here. She took my documentation as if to look at it, then wrote “take some advil”, handed it to me and said “talk to me when you get your degree”. I insisted they at least take blood and test. They did and some days or weeks later we received a letter from the CDC that it was RMSF.

      Fortunately for us, we had gone to an urgent clinic about 2 days earlier, they weren’t sure, but to be safe prescribed doxycycline.

  2. It would help to have Alpha Gal syndrome included in these studies. Lyme disease is at epidemic levels in Floyd, Va and a large portion of our residents have Alpha Gal syndrome. I have had Lyme disease 5 times since 2001 and have had AlphaGal for 3 years.

  3. I’m glad to hear CDC is working on the diseases brought about by Blacklegged ticks; and as bad as those ticks are, the ones known as Deer ticks spread what’s known as Alpha Gal which can cause all kinds on misery including anaphylaxis. Once the Alpha Gal sets in from the tick bite, eating any meat except fish and bird such as turkey or chicken is dangerous. This may sound easy to avoid, but also included in “meat” is cheese, glycerin, and a host of other foods containing meats. Luckily, to date no one has died from it to my knowledge but it’s a nightmare nonetheless.

  4. Why is there no record of ticks in British Columbia, Canada? Deer ticks are numerous here++++ I have had Babeosis & erlicheosis. Dr. E. Murakami. ( Professor Emeritus @ U.B.C. ) is a wealth of knowledge & I have to phone him several times & be treated. So many People on Pender Island unaware of crippling disease.

  5. All of these tick borne illnesses so dangerous if not treated. No money in it sorry to say. It’s all about the Covid.

  6. You cannot depend on the public to hand over results to you!!

    No body is gonna,
    ‘hand you the correct results’.

    Perform Tick Surveys on the ground,
    Every County, of every State, Every Year!!!

  7. Modern wildfire prevention is the largest cause of high tick populations. When fire burned regularly and naturally it kept their numbers down significantly. The only other thing that will kill them is a week or two at -30 degrees F.

    • regular prescribed fire return intervals is the way to control tick populations very well. Long periods of sub zero temperatures is a thing of the past. or maybe good old fashion bug repellent reapplied if necessary works really well for me and I spend a lot of time in the woods.

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