The prevalence and distribution of potentially pathogenic rickettsial agents in Ixodes ticks from the United States is poorly known. A total of 454 Ixodes scapularis Say were collected by flagging from vegetation or directly from field-exposed Army personnnel in various regions across the United States including Connecticut, Delaware, Minnesota, Wisconsin, and Georgia. Through PCR amplification, RFLP, and DNA sequencing of rickettsial rompA and gltA genes, we have characterized the distribution and properties of "Candidatus Rickettsia midichlorii" (previously called the Ixodes scapularis symbiont) in more detail. R. 'midichlorii' was present in 10-45% of adult male ticks, while significantly higher rates of infection were found in adult females in each area (33-100%). Egg batches (n=20) from 18 infected females from Connecticut and Georgia were all infected. A lab colony of Ixodes pacificus also exhibited high levels of infection with a related agent. Females (n=10) were all infected, while 70% of males (n=10) were infected. RFLP was done with gltA amplicons with AluI, PstI, and RsaI. For all samples tested from each region, patterns were identical for the rickettsiae from I. scapularis and I. pacificus. Sequencing analysis revealed that R. 'midichlorii' strains were identical in their rompA and gltA genes in each region. R. 'midichlorii' differs from R. 'cooleyi' detected in I. scapularis from Texas and from the closely related Rickettsia present in the lab colony of I. pacificus. These three agents each differ from the Rickettsia present in I. ricinus and I. persulcatus found in Europe.
Species 1: Acari Ixodidae Ixodes scapularis (blacklegged tick)
Species 2: Acari Ixodidae Ixodes pacificus (western blacklegged tick)
Species 3: Rickettsiales Rickettsiaceae Rickettsia midichlorii
Keywords: rickettsiae, symbionts
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