Rickettsiae, which may be symbiotic, have been reported in several ixodid ticks including Ixodes scapularis, the principle vector of many emerging pathogens. No information is available about the ecology and transmission of rickettsial agents in I.scapularis or about their effect on the tick's susceptibility to infection with known pathogenic organisms. Adult I.scapularis were collected by flagging from vegetation in the spring of 2002 and tested individually by PCR for the presence of Anaplasma phagocytophila, Borrelia burgdorferi, and Rickettsia spp. The identity of the rickettsial DNA in positive samples was established by restriction fragment length polymorphism (RFLP) analysis of both citrate synthase (gltA) and rOmpA gene fragments. The rickettsial DNAs present in all positive samples were identical by RFLP analysis for both genes. While the RFLP patterns obtained with rOmpA were identical to those described previously for I.scapularis agents from Texas (R.cooleyi)and Minnesota (IS symbiont), the gltA Alu I patterns obtained were found in I.scapularis from Delaware (R."midichlorii") but not R.cooleyi. Overall, more than 60% of questing adult ticks were positive for this Rickettsia. Tick populations at all four sites had comparable prevalence of infection. Females were significantly (p=0.0006) more often infected (25/31=81%) than males (8/32=25%). No correlation between the presence of this symbiont and infection with either A.phagocytophila, or B.burgdorferi, or both was found. Additional studies of the tissue distribution, transovarial transmission, and infectivity of R."midichlorii" will be required to understand the nature of its association with its tick host.
Species 1: Parasitiformes Ixodidae Ixodes scapularis (Black-legged tick)
Keywords: symbiont, co-infection
Back to Acarology Submitted Papers
Back to Informal Conferences
Back to The ESA 2001 Annual Meeting - 2001: An Entomological Odyssey