Adult ticks (Ixodes scapularis) infected with B. burgdorferi have increased overwintering survival, with implications for tick population growth

The tick, Ixodes scapularis, vectors pathogens such as Borrelia burgdorferi, the bacterium that causes Lyme Disease. Over the last few decades I. scapularis has expanded its range, introducing a novel health threat into these areas. Warming temperatures appear to be a major cause of this northward expansion. However, other factors are also involved. We show that adult ticks infected with B. burgdorferi have greater overwintering survival than uninfected ticks. Adult ticks were placed in individual microcosms and allowed to overwinter in both forest and dune grass environments. In the spring we collected the ticks and tested both dead and living ticks for B. burgdorferi DNA. Infected ticks had greater overwintering survival compared with uninfected ticks every winter for three consecutive winters in both forest and dune grass environments. The increased winter survival of adult female ticks could have a large impact on tick population growth, as we demonstrate. Our results suggest that, in addition to climate change, B. burgdorferi infection itself may be promoting the northern range expansion of I. scapularis. Our study highlights how pathogens could work synergistically with climate change to promote host range expansion.