title: Unique Strain of Rickettsia parkeri Associated with the Hard Tick Dermacentor parumapertus Neumann in the Western United States.
abstract: In 1953, investigators at the Rocky Mountain Laboratories in Hamilton, MT, described the isolation of a spotted fever groupRickettsia(SFGR) species fromDermacentor parumapertusticks collected from black-tailed jackrabbits (Lepus californicus) in northern Nevada. Several decades later, investigators characterized this SFGR (designated the parumapertus agent) by using mouse serotyping methods and determined that it represented a distinct rickettsial serotype closely related toRickettsia parkeri; nonetheless, the parumapertus agent was not further characterized or studied. To our knowledge, no isolates of the parumapertus agent remain in any rickettsial culture collection, which precludes contemporary phylogenetic placement of this enigmatic SFGR. To rediscover the parumapertus agent, adult-stageD. parumapertusticks were collected from black-tailed jackrabbits shot or encountered as roadkills in Arizona, Utah, or Texas from 2011 to 2016. A total of 339 ticks were collected and evaluated for infection withRickettsiaspecies. Of 112D. parumapertusticks collected in south Texas, 16 (14.3%) contained partialompAsequences with the closest identity (99.6%) toRickettsiasp. strain Atlantic rainforest Aa46, an SFGR that is closely related or identical to an SFGR species that causes a mild rickettsiosis in several states of Brazil. A pure isolate, designated strain Black Gap, was cultivated in Vero E6 cells, and sequence analysis of therrs,gltA,sca0,sca5, andsca4genes also revealed the closest genetic identity toRickettsiasp. Atlantic rainforest Aa46. Phylogenetic analysis of the five concatenated rickettsial genes placeRickettsiasp. strain Black Gap andRickettsiasp. Atlantic rainforest Aa46 withR. parkeriin a distinct and well-supported clade.IMPORTANCEWe suggest thatRickettsiasp. Black Gap andRickettsiasp. Atlantic rainforest Aa46 represent nearly identical strains ofR. parkeriand thatRickettsiasp. Black Gap or a very similar strain ofR. parkerirepresents the parumapertus agent. The close genetic relatedness among these taxa, as well as the response of guinea pigs infected with the Black Gap strain, suggests thatR. parkeriBlack Gap could cause disease in humans. The identification of this organism could also account, at least in part, for the remarkable differences in severity ascribed to Rocky Mountain spotted fever (RMSF) among various regions of the American West during the early 20th century. We suggest that the wide variation in case fatality rates attributed to RMSF could have occurred by the inadvertent inclusion of cases of milder disease caused byR. parkeriBlack Gap.
authors.affiliation: Rickettsial Zoonoses Branch, Division of Vector-Borne Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, USA cdp9@cdc.gov.
authors.forename: Christopher D
authors.initials: CD
authors.lastname: Paddock
authors.affiliation: Rickettsial Zoonoses Branch, Division of Vector-Borne Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, USA.
authors.forename: Michelle E J
authors.initials: MEJ
authors.lastname: Allerdice
authors.affiliation: Rickettsial Zoonoses Branch, Division of Vector-Borne Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, USA.
authors.forename: Sandor E
authors.initials: SE
authors.lastname: Karpathy
authors.affiliation: Rickettsial Zoonoses Branch, Division of Vector-Borne Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, USA.
authors.forename: William L
authors.initials: WL
authors.lastname: Nicholson
authors.affiliation: Rickettsial Zoonoses Branch, Division of Vector-Borne Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, USA.
authors.forename: Michael L
authors.initials: ML
authors.lastname: Levin
authors.affiliation: Texas Parks and Wildlife Department, Black Gap Wildlife Management Area, Alpine, Texas, USA.
authors.forename: Travis C
authors.initials: TC
authors.lastname: Smith
authors.affiliation: Utah Division of Wildlife Resources, Springville, Utah, USA.
authors.forename: Tom
authors.initials: T
authors.lastname: Becker
authors.affiliation: Center for Environmental Management of Military Lands, United States Army Dugway Proving Ground, Utah, USA.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Delph
authors.affiliation: Environmental Department, United States Army Dugway Proving Ground, Utah, USA.
authors.forename: Robert N
authors.initials: RN
authors.lastname: Knight
authors.affiliation: Infectious Diseases Pathology Branch, Division of High Consequence Pathogens and Pathology, Centers for Disease Control and Prevention, Atlanta, Georgia, USA.
authors.forename: Jana M
authors.initials: JM
authors.lastname: Ritter
authors.affiliation: Infectious Diseases Pathology Branch, Division of High Consequence Pathogens and Pathology, Centers for Disease Control and Prevention, Atlanta, Georgia, USA.
authors.forename: Jeanine H
authors.initials: JH
authors.lastname: Sanders
authors.affiliation: Department of Biochemistry, Molecular Biology, Entomology, and Plant Pathology, Mississippi State University, Starkville, Mississippi, USA.
authors.forename: Jerome
authors.initials: J
authors.lastname: Goddard
mesh_terms: D000818:Animals; D001130:Arizona; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics; D003870:Dermacentor / Q000254:growth & development / Q000382:microbiology*; D010802:Phylogeny; D011817:Rabbits / Q000469:parasitology; D012281:Rickettsia / Q000145:classification* / Q000302:isolation & purification*; D017422:Sequence Analysis, DNA; D017385:Sequence Homology; D013781:Texas; D014589:Utah
chemical_list: D001425:Bacterial Outer Membrane Proteins; C078167:OMPA outer membrane proteins
keywords: Dermacentor; RMSF; Rickettsia; Rickettsia Atlantic rainforest; Rickettsia parkeri; tick-borne pathogens