Wednesday, March 18, 2015

Are Backyard Birds Spreading Lyme Disease?

Most of us have heard about the connections between Lyme disease, mice and deer, who seem to be important vectors for the the disease, but it turns out a natural reservoir for Lyme disease may come in feathery form:

Researchers Identify Birds Hosting Lyme Disease
Researchers have discovered several bird species that host ticks carrying Lyme disease bacteria in northwestern California as well as another pathogen that causes chronic illness in humans.

“The role of birds in the maintenance of Lyme disease bacteria in California is poorly understood,” said Erica Newman in a release. Newman is a UC Berkeley Ph.D. student in the Energy and Resources Group at the University of California, Berkeley and lead author of a recently released study that “did a molecular study of bird blood, ticks present on the birds, and the associated species of bacteria that they were hosting.”

“This is the most extensive study of the role of birds in Lyme disease ecology in the western United States, and the first to consider the diversity of bird species, their behaviors and their habitats in identifying which birds are truly the most important as carriers.”
. . .
The teams study showed that the lesser goldfinch (Spinus psaltria), oak titmouse (Baeolophus inornatus) and the dark eyed junco (Junco hyemalis) were all competent hosts of Lyme disease bacteria (Borrelia burgdorferi) and harbored many more subtypes than other species. The golden crowned sparrow (Zonotrichia atricapilla) was found to be infected more frequently than other species. They also found, for the first time in the world according to Newman, that some bird species were hosting a related disease that humans can contract ­­— Borrelia bissetttii — which has infected people in Southern California and Europe.
That sounds suspiciously similar to the collection of birds visiting our feeder currently, Goldfinches, Titmice, Juncos and the occasional Sparrow. Slightly different species because we're on the East Coast and not the West, but a similar assemblage. I guess an important question is how readily the disease can be transferred from birds to humans. At least in the West, the principal tick that lives on birds, the Western Black-Legged Tick also transmits Lyme to humans. This is closely related to the Deer Ticks that transmit Lyme disease on the East Coast.

And there is some hint that the birds involved in the transmission of Lyme disease are beneficiaries of human habitation:
While chaparral shrub ecosystems tend to have high biodiversity with many species endemic to California, birds in those areas weren’t found to host Lyme disease at any significant rate.

But the birds that were found to host the disease were coincidentally the same bird species that happened to benefit from suburbanization in California, meaning they spend more time around humans.
It would be interesting to do a similar study out on the East Coast, the heart of the Lyme disease. Maybe you're (and our) bird feeder is contributing to the problem.

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