Global Warming and Tick-Borne Diseases

The tick population has exploded in Maine over the last 20 years. The reason? Global warming.

Yes, the reason is global warming. Since 1895, average temperature in Maine has risen about 3.6°F (2°C). More relevant is the fact that very cold temperatures have risen much more. Both winter faster than summer, and nighttime faster than daytime, have greatly reduced the effectiveness by which cold temperature helps control the tick population in Maine.

Overnight low temperature during the winter season (Dec-Jan-Feb) in Maine has already risen by a whopping 6.3°F (3.5°F).

Ticks have migrated further north, not just because they are better able to survive hard freeze when there’s so much less hard freeze. It’s also because their primary host species have migrated further north.

The best-known disease spread by ticks is Lyme disease. In 2001 Maine recorded 108 cases (according to the Maine CDC Infectious Disease Program). By 2017 that number had risen to 1,844 — seventeen times as many. More relevant is the number per capita, usually given as the rate per 100,000 people, which has risen from 8.4 to 138.5 — a “mere” sixteen and a half times as big.

Lyme isn’t the only disease spread by ticks, and it isn’t the only disease that has risen dramatically in Maine. The year 2001 saw no cases of anaplasmosis and only 1 case of babesiosis in the state, but 2017 brought 663 anaplasmosis infections and 118 of babesiosis. The rates of these rarer diseases were higher in Maine in 2017 than the rate of Lyme disease was in 2001.

Yes, the tick population has exploded. Yes, the rates of infectious disease spread by ticks have exploded. Yes, Mainers are suffering dread diseases, yes it costs money for medical treatment, yes it costs time and money for lost work and lost wages, yes it sometimes causes death.

And yes, it’s because of global warming.

It’s just one more reason that the politicians who obstruct aggressive action about global warming are working against the health and wellbeing of people. It’s time to make climate change your #1 issue in the voting booth.

Until we do, we’re living the joke about the word “politics” being the union of two words: “poly” meaning many, and “ticks” meaning blood-sucking parasites.

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19 responses to “Global Warming and Tick-Borne Diseases

  1. Nicely done. Do other states show such patterns? Particularly in other regions?

    • I heard on the radio just the other day of a case from Maryland where a woman developed food allergies (red meat and something else) from the bite of a lone star tick. Her physician asked a number of questions, including “Were you bitten by a tick in the last few weeks?” The lone star tick is another that has expanded its range recently.

  2. We’ve recently had our first confirmed case of Lyme’s disease in our town in Northern Ontario. And the vet told us that last week they had an infected black-legged tick pulled off someone’s dog (they tested the tick and confirmed it could transmit Lyme’s disease). We knew it would get here eventually as we were hearing tales from the southern cottage country as the infected ticks moved their way north.

  3. Yes, I’d love to see voters voting on one issue only, the environment, given the overwhelming importance of maintaining a habitable one for ourselves and our descendants. Sadly, other short-lived, relatively unimportant, issues keep getting in the way. Fingers crossed that some kind of tipping point is reached soon in the voting booths.

  4. The level of Lyme disease diagnosis is more than anything, proportional to the publicity and near hysteria generated by shows like Dr Oz and Oprah.

    [Response: Do you also believe that the similar dramatic increase of Anaplasmosis and Babesiosis is due to Dr. Oz and Oprah?

    It’s impressive that Oprah not only suckered Maine’s physicians and the Center for Disease Control, she also arranged for Lyme disease (and other diseases) to continued to rise SO dramatically in Maine, despite the fact that she isn’t on TV any more. And she must have been targeting Maine specifically, since more southerly states haven’t shown the same increase. She must be very powerful indeed.]

  5. You certainly cherry picked Maine.
    Some neighbour states to Maine (about the same latitude) have Lyme disease notifications falling over the decade.
    New York 2006 = 4460 , 2016 = 2623 (confirmed) + 1259 (probable) = 3882
    New Hampshire 2006 = 617, 2015 = 436
    And southern Texas increases 29 to 71 over the decade

    [Response: What??? They don’t get the “Oprah” show in New York or New Hampshire?????? My God, what is this world coming to?

    Thank you so much for giving me the inspiration for my *next* blog post. Stick around, you might even learn something (but I’m skeptical).]

  6. quaesoveritas

    Of course, as we know, correlation does not (always). imply causation.

  7. risen by a whopping 6.3°F (3.5°F)

    Think that’s supposed to be “3.5C”.

    [Response: Right you are.]

  8. Well, I’ll say this for Jeff; I appreciate him posting the link to the CDC tables. Looking at the state-by-state numbers, there are a couple of patterns that leap out. One is that many southern states have very low incidences of Lyme disease. Why? It’s certainly not an absence of deer, nor of ticks in general. Perhaps not the right species to carry Lyme?

    Another is that there are several northern-tier states that show a similar pattern to Maine, albeit much less marked (and probably not statistically significant yet). Michigan, for example.

    I wonder what would happen if you played around with binning this data in various ways? If I have time, I might give it a go.

    • Not an answer, Doc, but an interesting related article:
      Underreporting in particular in the southern states can be an issue.

      One warning from the CDC: case definitions have changed over the years, which puts some added uncertainty on trend analyses (see

      • Thanks for that, Marco–very interesting. I followed the links to the county-scale distribution study.

        Nice that my county, Kershaw, does not have a reported presence of the black-legged tick–though it must be admitted that that is an absence of evidence, not evidence of absence! (Especially since the species *has* been reported in Fairfield Co., just a mile or so across Lake Wateree.)

        For anyone who would like to drill down a bit, the direct link to the study is here:

      • Also interesting is the bi-coastal distribution. I didn’t expect that. But if you are in Kansas or Wyoming, you needn’t worry about Lyme disease, unless you travel.

        Since we were speaking of spurious correlations above, an example might be the apparent correlation between a preponderance of politically liberal views, and Ixodes scapularis or Ixodes pacificus.

  9. “6.3°F (3.5°F)” is a typo.

  10. This is what I found a couple of years ago in central Minnesota.
    The Lone Star Tick is moving north in range due to global warming, As mentioned above these ticks can trigger meat allergies

    Took out the microscope and took the photo on the left and compared to the right. Note the distinctive yellow spot.