Species composition and prevalence of Borrelia infections in Ixodes spp. ticks from the southeastern coastal United States

ABSTRACT: The classic Lyme borreliosis (LB) cycle, involving the vector Ixodes scapularis and the etiological agent Borrelia burgdorferi sensu stricto (Bbss), has been well documented in the Northeastern US, where this disease is becoming increasingly prevalent in humans and dogs.  In the Western US, the LB cycle involves two tick species: Ixodes spinipalpis (critical for sylvatic cycles of the pathogen) and I. pacificus (the primary vector to humans).  Recently, in coastal regions of North Carolina, I. affinis has been shown to have a higher incidence of Borrelia burgdorferi sensu lato (Bbsl) than does I. scapularis. This raises the possibility that LB in the Southeastern US involves multiple tick species, with I. affinis maintaining Bbsl in sylvatic cycles similar to those seen in the West. I. affinis is not known to be a human-biting tick, so the shift from an Ixodes scapularis-dominated LB cycle in the northeast to an I. affinis-dominated cycle in the Southeast may help explain the low prevalence of LB cases in southeastern states.  Nevertheless, other Ixodid tick species in the Southeast, such as I. angustus and I.minor, do occasionally parasitize human hosts, so low-level LB transmission is a possibility in southeastern states if there are sylvatic cycles of Bbsl involving I. affinis. Changes in prevalence of Bbss in I. scapularis and I. affinis along a North-South gradient from southern Virginia into South Carolina will be described, and their potential implications for Lyme disease risk in humans and canines will be discussed.