Bad Lyme Disease Spring Predicted For Northeast, Begin Vigilance Now

acorns

toomas-marit.hinnosaar.net

This just in from the Cary Institute of Ecosystem Studies: We in the Northeast should expect an unusually large surge of Lyme disease this spring.

It’s not the extraordinarily mild winter that’s to blame, it’s the fluctuation of mouse populations and acorn harvests. (More on that later.) But the mild winter may mean that the danger period, when tiny young “nymph” ticks that carry Lyme are out for our blood, could begin earlier than usual. The bottom line from Dr. Richard S. Ostfeld, a Cary Institute disease ecologist: Watch out. Starting now.

Normally, Lyme disease risk ramps up in May. But “This past winter,” he said “was record-breaking mild, and when you get records, when you have extremes in weather events, to some degree all bets are off. We don’t really know whether the nymphs are going to start their activity earlier this year than in normal years. So it’s remotely possible they could be out as early as April. They’re cold-blooded creatures, so things get speeded up in terms of their metabolism and development when things are warmer. So it could be a bit earlier than usual. I wouldn’t wait to be vigilant. The time is now.” (What does such vigilance look like? Here are prevention tips from the CDC.)

I asked Dr. Ostfeld if he could offer some order of magnitude of the expected surge in Lyme disease. Very, very roughly, he said, we could see perhaps 20 percent more cases than usual.

Acorn production in 2010 set a record for the 20-plus years it has been monitored, he said, “and mouse abundance in the summer of 2011 was oh, perhaps 10 or 20 percent higher than we’ve ever recorded. So I would expect the Lyme disease risk should be at least that much higher than we’ve had in the past.” He emphasized: “This is a prediction based on past trends, and in ecology, as in economics — what do they say about stock portfolios? — past performance does not predict future returns. But that’s my best estimate as to what might happen.”

Now for a bit of the ecology behind the predictions. From the Cary Institute’s press release:

What do acorns have to do with illness? Acorn crops vary from year-to-year, with boom-and-bust cycles influencing the winter survival and breeding success of white-footed mice. These small mammals pack a one-two punch: they are preferred hosts for black-legged ticks and they are very effective at transmitting Borrelia burgdorferi, the bacterium that causes Lyme disease.

“We had a boom in acorns, followed by a boom in mice. And now, on the heels of one of the smallest acorn crops we’ve ever seen, the mouse population is crashing,” Ostfeld explains. Adding, “This spring, there will be a lot of Borrelia burgdorferi-infected black-legged ticks in our forests looking for a blood meal. And instead of finding a white-footed mouse, they are going to find other mammals—like us.”

For more than two decades, Ostfeld, Cary Institute forest ecologist Dr. Charles D. Canham, and their research team have been investigating connections among acorn abundance, white-footed mice, black-legged ticks, and Lyme disease. In 2010, acorn crops were the heaviest recorded at their Millbrook-based research site. And in 2011, mouse populations followed suit, peaking in the summer months. The scarcity of acorns in the fall of 2011 set up a perfect storm for human Lyme disease risk.

Black-legged ticks take three bloodmeals—as larvae, as nymphs, and as adults. Larval ticks that fed on 2011’s booming mouse population will soon be in need of a nymphal meal. These tiny ticks—as small as poppy seeds—are very effective at transmitting Lyme to people. The last time Ostfeld’s research site experienced a heavy acorn crop (2006) followed by a sparse acorn crop (2007), nymphal black-legged ticks reached a 20-year high.

The May-July nymph season will be dangerous, and Ostfeld urges people to be aware when outdoors. Unlike white-footed mice, who can be infected with Lyme with minimal cost, the disease is debilitating to humans. Left undiagnosed, it can cause chronic fatigue, joint pain, and neurological problems. It is the most prevalent vector-borne illness in the U.S., with the majority of cases occurring in the Northeast.

Ostfeld says that mild winter weather does not cause a rise in tick populations, although it can change tick behavior. Adult ticks, which are slightly larger than a sesame seed, are normally dormant in winter but can seek a host whenever temperatures rise several degrees above freezing. The warm winter of 2011-2012 induced earlier than normal activity. While adult ticks can transmit Lyme, they are responsible for a small fraction of tick-borne disease, with spring-summer nymphs posing more of a human health threat.

Past research by Ostfeld and colleagues has highlighted the role that intact forest habitat and animal diversity play in buffering Lyme disease risks. He is currently working with health departments in impacted areas to educate citizens and physicians about the impending surge in Lyme disease.

Further reading

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  • Featherjourney

    I live in North Central MA and as of mid March I have already taken 3 deer ticks off of my house cat (who meanders around outside and in the woods) in the past couple weeks.   I had lyme 3 summers ago, following the big ice storm and the huge amount of clean up from all the tree damage that happened.  That was the year that the deer tick population seemed to explode around here.  I think that ice storm event really spread them around.  We also have a colony of feral cats (all trapped, neutered, and spayed!) in our barn – I often see engorged deer ticks on them.  I do think the cats as well as fox, squirrels, etc. all spread them around and bring them into the yard.  It isn’t just the deer.  The nymph stage ticks are so tiny!  You really need a magnifying glass to see that the speck you are looking at is indeed a tick!

  • Leslee

    I live in the Berkshires ( Western MA). Basically.All winter,  anytime we have had a warm day,
    I taken a tick or 2, mostly just crawling, from my dog’s coat. In the last 3 days, I have
    been taking between 6-12 ticks from her coat. This am, after our usual hour walk along
    a wooded road, but not in the woods, I removed 12 ticks. I brush her thoroughly, and then
    take a very fine tooth flea comb to her coat. It is when I take the flea comb to her that I 
    pick up the ticks. Happily she is getting a major stripped down haircut on Monday, but
    this will not make me any less vigilant. Checking once a day is simply not enough. If you
    want to catch them before they imbed, check each time you are out, even if you have only
    been out for a few moments.

  • Tickkilla

    2 days ago 5 ticks on the South facing side of house foundation. Wellesley MA

  • https://identify.us.com IdentifyUS

    The proposed links between acorn abundance, mouse abundance and risk of infection are interesting but quite controversial. Tick abundance is far more closely linked to deer abundance.  Infection risk is a product of the abundance of ticks, mice, deer and other animals, weather conditions, human exposure and yet other factors. It may be that the unseasonably warm weather throughout the region may actually have burdened many ticks that normally would be protected by a layer of snow.  Time will tell.

    Whereas many physicians will administer a presumptive dose of antibiotics to patients who have been fed upon by a tick, this is reasonable only if the tick: 1) is a deer tick (dog ticks, for example cannot transmit the agent of Lyme disease); 2) is a nymphal or adult deer tick (larvae cannot transmit that infection); and 3) has fed for about two or more days (removing deer ticks promptly can dramatically reduce risk of infection). These assessments can be made quickly by examining the tick or a good digital image. More information about that process can be found online.  -Richard Pollack, PhD

    • Jasper

      I had thought that the research involving the relationships between deer and ticks was lacking in controls, did not take into account the prevalence and dynamics of other potential host species, and still often failed to show a correlation between deer abundance and tick abundance — still less between deer abundance and the abundance of infected ticks.  Is there new research involving deer that resolves those issues?  If so, I would be interested in links to those studies. 

      • https://identify.us.com IdentifyUS

        Each deer may support the feeding of hundreds or even thousands of deer ticks each season. Each female deer tick can then produce ≤2,000 eggs.  The abundance of deer, then, is the most significant factor in contributing to the abundance of deer ticks.  Immature deer ticks become infected by feeding upon infected mice, so the local abundance and infection rate of mice are critical factors contributing to the infection rate within those ticks. For an excellent overview of Lyme disease, including the role of deer, mice and other animals in this complex system, see: http://www.ct.gov/caes/lib/caes/documents/publications/bulletins/b1010.pdf

  • Wendydoremus

    I pulled a live tick off of a friend in January 2012 in central (Hopkinton) Massachusetts after we took a stroll in the woods.  After my own severe bout (and ongoing problems with) a “lyme-like” illness (not positively verified by lab tests) two years ago, I recommend that ANYONE who has had an embedded deer tick request prophylactic antibitiotic treatment. Though the current general trend is to limit antibiotic prescriptions, this is one situation where it is absolutely warranted.

    Wendy Doremus

    • Leslie Farhangi

      Yes, there is a study published in the New England Journal of Medicine finding that one dose of doxycycline was effective as a preventative.  Some doctors believe two doses, or four doses (two days) is better, but there are no studies on that.  There is, as I said, a study about the one dose.  Not all doctors seem aware of even that.