Things we're not sure about Why Ixodes ricinus is increasing its geographical range If newly hatched Ixodes ricinus larvae can carry the bacteria that cause Lyme disease If a tick can infect a human with the bacteria that causes Lyme disease as soon as it bites If deer can spread Lyme disease ‹ The hosts involved in transmitting the bacteria that cause Lyme disease Why Ixodes ricinus is increasing its geographical range ›