Gulf Coast Ticks (Amblyomma maculatum) and Rickettsia parkeri, United States

Geographic distribution of Rickettsia parkeri in its US tick vector, Amblyomma maculatum, was evaluated by PCR. R. parkeri was detected in ticks from Florida, Georgia, Kentucky, Mississippi, Oklahoma, and South Carolina, which suggests that A. maculatum may be responsible for additional cases of R. parkeri rickettsiosis throughout much of its US range.


Gulf Coast Ticks (Amblyomma maculatum) and Rickettsia parkeri, United States
The Study A. maculatum ticks collected during 1996-2005 were evaluated by molecular methods for evidence of infection with R. parkeri.Ticks were collected from various locations in Florida, Georgia, Kentucky, Mississippi, Oklahoma, and South Carolina.Most were questing adults collected from vegetation by using fl annel cloth fl ags; a few crawling, nonattached, nonengorged adults were obtained (4 from a coyote and 3 from human hosts), and 1 engorged nymph was removed from a cotton rat.Ticks were preserved in 70% ethanol or frozen at -80ºC until evaluation.
Most individual ticks were minced with a sterile scalpel blade, and DNA was extracted by using a QIAamp Mini Kit (QIAGEN, Inc., Valencia, CA, USA).Others were minced or crushed after freezing in liquid nitrogen, and DNA was extracted by using an IsoQuick nucleic acid extraction kit (ORCA Research, Bothell, WA, USA).DNA extracts were evaluated by using nested or heminested PCR assays designed to amplify a segment of the rompA gene.Photographs courtesy of James Gathany, Centers for Disease Control and Prevention to gel electrophoresis, and products of the appropriate size were excised.DNA was purifi ed from the gel fragments by using the QIAquick Gel Extraction Kit (QIAGEN).Purifi ed PCR products were sequenced using the PCR primers and the GenomeLab DTCS Quick Start Kit (Beckman Coulter, Fullerton, CA, USA).For some products, additional sequencing primers 190-SF3 (5′-GGT ACT ACT CCC GTA GGT C-3′) and 190-SR2 (5′-CCG GCA GTA AKA GTA ACA G-3′) were used to obtain complete sequences for both strands.Sequences were detected by using a Beckman CEQ 8000 automated sequencer.Sequence similarities were determined by using the BLAST program (version 2.0, National Center for Biotechnology Information, www.ncbi.nlm.nih.gov/blast).Sequence-length reaction products (excluding primers) were 590 bp for primary, 559 bp for heminested, and 540 bp for nested.
Precise estimates of infection prevalence could not be assessed from these data because most of the ticks evaluated in this study were collected as relatively small sample sizes or were collected in a discontinuous manner as multiple samples from the same sites over several weeks or months in a given year.However, some collections were fl agged synchronously at a single location, including those in Copiah County, Mississippi, during July 2002 (n = 9) and in Franklin County, Florida, during July 2004 (n = 25) and July 2005 (n = 27).Infection prevalence for each of these 3 collections was 11%-12%, which suggests that R. parkeri may be a relatively common inhabitant of some populations of Gulf Coast ticks.By comparison, the estimated prevalence of infection of tick vectors with R. rickettsii, the etiologic agent of Rocky Mountain spotted fever (RMSF), is typically much lower, as determined by surveys elsewhere, which identifi ed R. rickettsii in only 0.05%-1.3% of the collected specimens: 3,705 Dermacentor andersoni ticks from canyons bordering the Bitterroot Valley of Montana; 2,123 and 310 D. variabilis ticks from RMSF-endemic areas of North Carolina and Ohio, respectively; and 669 A. aureolatum ticks from São Paulo, Brazil (11)(12)(13)(14).

Conclusions
R. parkeri has been isolated in culture from Gulf Coast ticks collected in Alabama, Florida, Georgia, Mississippi, and Texas ([2,7,8], C. Paddock, unpub.data).These re-  (15) indicate that much remains to be learned about R. parkeri and other rickettsiae of human-biting ticks in the Western Hemisphere and their relative contributions to the epidemiology of New World spotted fevers.
Mr Sumner is a molecular biologist at the Centers for Disease Control and Prevention, where he has worked extensively on the molecular detection of various Rickettsia, Ehrlichia, and Bartonella spp.for >15 years.His research interests now focus primarily on PCR-based evaluation of formalin-fi xed tissues for bacterial and viral pathogens.

Table . Gulf
Coast ticks (Amblyomma maculatum) infected with spotted fever group rickettsiae, United States, 1996-2005 , combined with data from the present study, suggest that in the United States R. parkeri can be found anywhere that A. maculatum ticks are found.In this context, persons exposed to habitats in any region infested by Gulf Coast ticks are potentially vulnerable to infection with R. parkeri.A previously undescribed rompA sequence, identifi ed in a few ticks collected during this survey, may represent a novel species of spotted fever group rickettsiae associated with the Gulf Coast tick.Attempts to isolate and characterize this species are in progress.Collectively, these fi ndings suggest that the role of A. maculatum in the ecology of various spotted fever group rickettsiae deserves further attention.These results and the recent discovery of R. parkeri in A. triste ticks in Uruguay sults