Recently, it was found in the US that some strains of B. burgdorferi, sensu stricto, cause severe disease, whereas others cause mild, self-limiting disease. The effect of LD is based on the strains of B. burgdorferi. The Ixodes species tick transmits the bacterium resulting in a systemic illness from spirochete bacterial infection of Borrelia burgdorferi. It so happens the tick is a mobile septic tank that transmits many diseases, known as the Lyme’s co-infections. This is discussed later in greater detail. The persistence of the LD spirochete in the host, is its ability to evade the immune system through its dynamic morphology.