Wednesday, February 8, 2012

7 The New Tick Map Vs. The Atlantic Flyway: Things That Make You Go Hmm.

[Ed. - Overlay map revised Feb. 9, 2012.]

Well, I guess everyone has seen this map from Yale University by now...


Yes, it is a map of Lyme disease risk areas based on tick flagging from 2004-2007 in the above regions, followed by an analysis of those ticks. No matter where one looked, the odds of a tick carrying Borrelia burgdorferi were 1 in 5 everywhere... So be careful out there, huh?

While it's good to let people know there are transition areas where Lyme disease is up and coming, it's good not to be too complacent if you fall into a green zone. Today's low risk zone can be tomorrow's transitional area, and these maps must be accurately updated in order to reflect reality.

Thing is, I haven't been thinking of this map as regards tick distribution and Lyme disease so much as I've been thinking about this map:


Because there is evidence that ticks' distribution is spread not only by mammals which hug the ground - but can also be spread geographically by birds. 

So look at the above two maps. Now look at this, after I scale and resize them to overlap (somewhat off-bias, but best I could get with different projections):


Questions for my readers:
  • For those of you along the southern principal flyway, how many of you received an infected tick bite near that flyway, either to its north or south?
  • For those of you in northeastern and north central Florida, how many of you received an infected tick bite near that flyway passing over your state?
  • For those of you in eastern Canada, can you tell me if you received an infected tick bite near that flyway by the Great Lakes?

I'm looking at this and wondering a few other things, too, like I think these flyways would end up moving a little further north as global warming progresses - so I would expect a greater distribution of infected ticks further north as time goes on. Is there any way to confirm this is what is happening?


7 comments:

  1. I'm going to post a link to this blog entry on the CanLyme forum. Hopefully this will increase your chances of getting responses from those who live in eastern Canada.

    Although there are a few published articles that support the theory Lyme disease is being spread at least partly by migrating birds, I don't believe anyone else has taken the time to overlay the two maps as you have done. What a great idea!

    Rita

    ReplyDelete
  2. Interesting that you overlayed the maps. I am in NC, not in a flyway and we still have plenty of infected I scaps. Nothing like the NE, of course, but, who wants one, possible even where there are fewer. I see lots of problems with this Yale study and lots of harm for the south. Our local press is coming out with headlines about the study saying there is almost no risk of Lyme disease in our state or the rest of the south. Funny, since one NC county was declared endemic a couple of years ago and several more are on the way to meeting the very stringent requirements for that label.

    ReplyDelete
  3. Rita,

    Thanks for posting to CanLyme. Hopefully people will respond and say what their experience has been with ticks in eastern Canada. When was the last time that area was actively flagged and surveyed? Does anyone know? Who does the surveillance there?

    Anonymous,

    I agree that this map could do more harm than good for some people. If you already have it on record that specific counties in NC are endemic (judging from Yale's map, NC has only a splash of transitional area on the coast), then that needs to be made clear to medical care providers and everyone living in and visiting that area that it is endemic. All the data at hand needs to be factored in - not just the results of this tick flagging expedition.

    If you are the poor soul who gets bitten by an infected tick in a low risk area, doctors still need to keep Lyme disease and other tickborne diseases in mind anyway because the rate and distance at which infected tick populations expand is unpredictable. (Occasionally local populations actually contract due to a variety of environmental factors, but this is less likely than expansion in recent years.)

    ReplyDelete
  4. CO,

    I've posted some information on the CanLyme forum, and have asked folks there to post any additional details they may be aware of. To the best of my knowledge, there have been very few attempts at active surveillance, and those have been carried out in very select locations. It is largely passive tick surveillance that is currently being conducted in Canada, but Public Health Ontario stated in July 2011 that active surveillance of the ticks that carry Lyme disease is now part of their mandate.

    On a federal level, the Public Health Agency of Canada works in partnership with the provinces and territories -- at least theoretically -- to establish risk factors for Lyme disease. The Canadian Institutes of Health Research funds some of these studies.

    An elected member of the Canadian Parliament's House of Commons recently tabled a number of pointed questions having to do with Lyme disease. The Government of Canada is required to officially respond to those questions in 45 (sitting) days, and I'm hoping this will help to clarify details about tick surveillance methods and much more.

    Active surveillance is nothing new when it comes to mosquitoes that may carry West Nile Virus in Canada, so I'm not exactly sure why similar measures haven't been considered a priority when it comes to Lyme disease. Then again, it seems that data from passive surveillance is used to target those areas in need of more active surveillance. Since Lyme disease is found predominantly in southern Canada, there is certainly a lot of geographic territory to cover, and since the official rates of Lyme disease in Canada remain low, active surveillance may be considered too costly to conduct on a large scale.

    I would really like to see much more in the way of active surveillance being carried out in Canada (and elsewhere) -- and particularly in those "non-endemic" areas where people with no history of travel are being infected in increasing numbers.

    ReplyDelete
  5. CO,

    I forgot to include two links that describe a 2-day Canadian “National Lyme Disease Meeting” held in Toronto during March 2006. The list of participants (many from the U.S.) is impressive, and I only wish there had been some follow-up with regard to the recommendations and the “next steps” outlined in the second link. While the meeting looked like a great start, it appears that further meetings weren’t deemed necessary. No one really seems to know why.

    http://www.phac-aspc.gc.ca/id-mi/lyme032006-eng.php

    Quote:

    The two-day meeting included presentations which addressed epidemiological, ecological, diagnostic, public health, communications and ethics perspectives and identified significant research findings and issues relating to Lyme disease in Canada and the United States. The plenary sessions provided updates and current information on the epizootiology, diagnosis and laboratory testing, human epidemiology and surveillance, and information and communication of Lyme disease issues.

    The tick vector of B. burgdorferi in eastern and central Canada, Ixodes scapularis, has steadily expanded its range in the United States over the last 30 years, and similar range expansions have been observed in parts of southern Manitoba, eastern Ontario, and Nova Scotia in recent years. The need for systematic sampling for ticks together with ecological risk modelling was identified as key to developing predictive risk maps.

    The role of migrating passerine birds in transporting vector ticks (I. pacificus and I. scapularis) was demonstrated to be one important mechanism for range expansion, and could help to explain the occurrence of human Lyme disease cases in parts of Canada where the vector ticks are not known to be established. The major bird migration routes transect Lyme disease endemic areas of the United States and Canada. Spring migrating birds stop-over to feed at times that coincide with the seasonal activity of immature stages of I. pacificus and I. scapularis. This has potential to impact the future range of ticks as well as areas of risk of human infection in Canada.

    [end quote]

    Many more details, including those related to surveillance efforts in both the U.S. and Canada, are available here:

    http://www.phac-aspc.gc.ca/id-mi/pdf/lyme032006_e.pdf

    ReplyDelete
  6. Hi CO,

    I just came across this information about a change in the surveillance strategy for the province of Nova Scotia -- in the eastern part of the Atlantic flyway zone:

    source: http://www.saltscapes.com/index.php?option=com_content&view=article&id=1426&catid=27&Itemid=53

    Lyme Disease and Ticks

    Written by Donna D'Amour. Photography by Donna D'Amour. This article was published in the Spring 2012 issue of Living Healthy in Atlantic Canada.

    What you need to know before (and after) you take that walk in the woods.

    [snip]

    Until September of last year, a province-wide passive survey was being conducted by the Nova Scotia Department of Health and Wellness; the public, veterinarians and physicians were welcome to submit specimens. The Department of Health and Wellness no longer needs to receive ticks for testing or surveillance purposes. The focus has now shifted from both passive and active surveillance to solely active fieldwork, studying areas where tick populations are expanding. Department of Natural Resources officials now visit sites from which multiple ticks have been submitted and check squirrels, mice, and other small mammals for ticks.

    [snip]

    ReplyDelete
  7. Rita,

    Thanks for sharing this piece of information. It sounds like Nova Scotia is investing more resources in intense environmental studies than they were earlier. I hope this is the beginning of an expanded effort to find out how ticks are getting there (mammals or avian hosts) and which pathogens they are carrying. Canada is in need of these studies.

    ReplyDelete

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