Lyme disease caused by the spirochete Borrelia burgdorferi is the leading vector-borne illness in the United States (1). The natural infectious lifecycle of B. burgdorferi is complex in that it is necessary for the bacteria to colonize both an arthropod vector (the Ixodes scapularis tick, pictured right) and a mammalian host (2). As the bacteria transitions between those two diverse niches, it alters the expression of its major outer surface proteins (Osps) such that expression of those that…