Canadian Lyme researcher John D. Scott’s studies of songbirds in Ontario, Canada have found that ground-foraging birds such as sparrows, warblers, wrens, juncos, and thrushes (including the American Robin) are often infested with Lyme disease ticks.
In a study between 2007 and 2009, Scott reported that 481 ticks were collected from 211 songbirds in Canada. Collecting methods included using mist-netting to trap birds who were then banded and checked for ticks before being released and retrieving dead birds that had crashed into city office buildings and fallen to the pavement.
Researchers found multiple species of ticks on the songbirds, some of which are not known to carry Lyme. However, six species of Ixodes ticks were positive for Borrelia burgdorferi (I. auritulus, I. fentatus, I muris, I. pacificus, I. scapularis, and I. spinipalpis). Most surprising was the finding that Ixodes ticks were capable of passing Lyme from one Ixodes species to another while attached to the birds.
What do these findings mean for our understanding of the prevalence and dissemination of Lyme? Plenty!
First, songbirds migrate long distances. Migration patterns between Canada and Central and South America allow birds to spread Lyme ticks across North America twice a year, in the spring and fall, following four major North American flyways that cross coasts, mountains, and principal river valleys already known as Lyme Disease hot spots. The four flyways are:
Atlantic Flyway – East coast of South America, Leeward Islands, the Bahamas, East coast of the US to the upper Midatlantic states, where it splits into four branches: 1) the Upper US Midwest northwest through midCanada, 2) the Upper US Midwest north through Ontario, 3) the US Northeast through Quebec. and 4) up the Eastern coasts of the US and Canada.
Mississippi Flyway – West coast of South America over the Gulf of Mexico to Mississippi, where it splits into four branches:1) Northeast through the Upper Midwest to Eastern Ontario and Quebec, 2) North through the Western Great Lakes to Western Ontario. 3) Northwest through the middle of the US to Manitoba, and 4) Northwest through the middle of the US just west of through Saskatchewan.
Central Flyway – Five routes from Central and Eastern Mexico through the interior Western US states to Alberta and Saskatchewan and north.
Pacific Flyway – West Coast of Central America, West coast of the US, West coast of Canada, with a second branch in Canada going through Alberta.
Second, not only do songbirds provide long-distance transportation for Lyme-infested ticks, they serve as another reservoir host for B. burgdorferi bacteria.
This latter finding puts a major dent in the popular belief that deer are the main reservoir hosts for Lyme. Often we hear of efforts to cull deer to reduce their population (and presumably reduce the incidence of Lyme). That kind of preventive measure is unthinkable with birds. Moreover, songbirds can carry a variety of Lyme-infected ticks that can produce a wider range of clinical symptoms and blood responses in humans than is currently known.
Pioneers like John Scott help push the boundaries of our knowledge about how infectious diseases are transmitted. Clearly, Lyme Disease exists as part of a more complex ecosystem than most of us realize.
Given Scott’s songbird studies, doctors who doubt that Lyme exists in their area should think twice before telling their patients “You couldn’t possibly have Lyme because there are no deer around here.”
You can watch a free 8-min. clip of Scott’s 2011 ILADS songbird presentation here. On that page you can also buy his video set for 15 USD, which includes an encrypted online link to view his powerpoint slides and presentation video.
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