Birds, Ticks, and Lyme Disease
White-tailed Deer, White-footed Mice, and Deer Ticks Support Lyme Disease Spread – So Do Birds.
Jul 10, 2006 Rosemary Drisdelle
Lyme disease hosts
What do birds have to do with the spread of Lyme Disease? Many people know that White-tailed Deer carry the tick that transmits Borrelia burgdorferi (the organism that causes Lyme disease) to humans. Many people also know that the deer carries and feeds the tick, but it's the White-footed Mouse that usually gives B. burgdorferi to the tick in the first place and serves as a reservoir in nature for the organism. Few people realize that birds, too, play an important role in the spread of Lyme disease to new locations.
Where do birds fit in?
Birds can transport B. burgdorferi in two ways, both of which start with a tick - usually the deer tick, Ixodes scapularis (on the North American West Coast, the tick is Ixodes pacificus). When ticks are ready for a blood meal, they hang around in tall grasses and other brushy plants, waiting for a warm blooded animal to happen by. If the first potential host to arrive is a bird, the tick is happy to climb aboard. It finds its way between the feathers, selects a feeding site, and buries its mouthparts in the bird's tender skin.
Either the bird or the tick may already be infected with B. burgdorferi. If so, by the time the tick finishes feeding and drops off the bird, they will both have it - and because ticks take days to feed and birds migrate, the pair is likely to be miles away from where they met. Both can go on to pass the organism to new ticks, birds, mice and people (though only the tick can pass it directly to warm blooded vertebrates like birds, mice, and people).
Lyme disease goes north
So birds can either carry infected ticks to new places, or carry Borrelia burgdorferi to new ticks. This is apparently the route by which Lyme disease has spread from the Northeastern United States to many other areas, including southern Canada. Any place where there is a suitable host tick or a climate that will support the survival of the Ixodes carrier ticks, will become an endemic area for the disease.
Why now?
The question arises as to why B. burgdorferi is spreading now. Deer ticks and migrating birds have been crossing paths for a very long time. Why didn't Lyme disease spread many years ago? Two reasons stand out: the number of deer in eastern forests is extraordinarily high resulting in huge numbers of ticks, and, global warming with less severe winters has expanded the range in which the ticks can survive year round to establish a breeding population.
Unfortunately, it's a trend that seems likely to continue for the foreseeable future.
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