Female ticks (Ixodes scapularis) infected withBorrelia burgdorferihave increased overwintering survival, with implications for tick population growth

Abstract

The tick,Ixodes scapularis, vectors pathogens such asBorrelia burgdorferi, the bacterium that causes Lyme Disease. Over the last few decadesI. scapularishas expanded its range, introducing a novel health threat into these areas. Warming temperatures appear to be one cause of its range expansion to the north. However, other factors are also involved. We show that unfed adult female ticks infected withB. burgdorferihave greater overwintering survival than uninfected female ticks. Locally collected adult female 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 forB. burgdorferiDNA. Infected ticks had greater overwintering survival compared with uninfected ticks every winter for three consecutive winters in both forest and dune grass environments. We discuss the most plausible explanations for this result. The increased winter survival of adult female ticks could enhance tick population growth. Our results suggest that, in addition to climate change,B. burgdorferiinfection itself may be promoting the northern range expansion ofI. scapularis. Our study highlights how pathogens could work synergistically with climate change to promote host range expansion.