The range of Lyme disease is gradually spreading in North America, and according to researchers, birds are playing a significant role. Robert Brinkeroff, a post-doctoral student at the School of Public Health, insists that “birds are often overlooked in Lyme disease studies, but they may be playing a key role in its rapid expansion”. Lyme disease is currently endemic in areas of six Canadian provinces: British Columbia, Manitoba, Ontario, Quebec, New Brunswick and Nova Scotia. However, in the near future most Canadians will likely live in regions where Lyme disease in endemic, largely due to the ease in which birds can transport the disease.
One of the key transporters of Lyme disease is the songbird. While known for their cheerful songs, the birds are not as innocuous as they sound – some of them transport tiny, disease-carrying ticks. Researcher John D. Scott and his colleagues conducted a study and found that 35% of the nymphs of black-legged ticks collected from songbirds in central and eastern Canada are infected with Lyme disease bacterium. The most frightening aspect of disease-carrying birds is the amount of ground they are able to cover, ensuring no geographical region will be completely exempt from potential tick-borne diseases.
During spring migration, songbirds from South America transport ticks to Canada from as far as Brazil. Additionally, ticks on songbirds have been found as far north as Slave Lake, Alberta and even parts of the Yukon. Extreme climates in Canada are no match for the black-legged tick, either – these ticks are eco-adaptive because they have anti-freeze like compounds in their bodies and are able to withstand outdoor air temperatures of up to -40 Celsius. It should go without saying that the black-legged tick will remain endemic in Canada for some time.
While birds are far from the only animal playing a role in maintaining and spreading tick populations, they are more prone to spreading disease. The white-tailed deer is a very common and reliable host for ticks, however they are a biological dead-end for the bacterium because its blood is immune to infection. Conversely, birds are not immune, and numerous species are capable of transmitting infections to ticks. It remains to be seen whether the strains that can infect birds also cause disease in humans. Erica Newman, a postdoctoral researcher in ecology at the University of Arizona, believes birds will be an important part of a northward spread of Lyme disease due to their migratory travels, “as much as or even more so than small mammals”. Birds found to be particularly competent as reservoirs for Lyme disease include American robins, dark-eyed juncos, and the golden crowned sparrow.
With an estimated 45 million to 175 million black-legged ticks entering Canada every year, and the fact that migratory birds are often selected as their hosts, birds are proving to be a big problem in the spread of tick borne diseases.