Do birds affect Lyme disease risk? Range expansion of the vector-borne pathogen Borrelia burgdorferi

Because of their capacity for long-range movement, birds may play an important role in the spread and range expansion of zoonotic pathogens and their vectors. The black-legged tick ( Ixodes scapularis ) is the principal vector for the Lyme disease bacterium Borrelia burgdorferi , and commonly parasitizes a wide variety of vertebrate hosts, including at least 71 species of North American birds. Although the role of birds in B burgdorferi transmission dynamics is often discounted, data compiled from published studies indicate that the majority (58.6%%) of bird species that have been evaluated are capable of infecting larval I scapularis with B burgdorferi . We estimated -– for two bird species -– that the number of individual birds required to produce one infected I scapularis larva is as low as three, and we conclude that bird-mediated tick movement is an important factor in the range expansion of both I scapularis and B burgdorferi .