| Rickettsia parkeri | |
|---|---|
 | |
| Rickettsia parkeri rickettsiosis skin lesions: A -eschar after tick bite on neck; B, C -papulovesicular rash on back and leg; D -micrograph ofbiopsy specimen | |
Scientific classification | |
| Domain: | Bacteria |
| Kingdom: | Pseudomonadati |
| Phylum: | Pseudomonadota |
| Class: | Alphaproteobacteria |
| Subclass: | "Rickettsidae" |
| Order: | Rickettsiales |
| Family: | Rickettsiaceae |
| Genus: | Rickettsia |
| Species group: | Spotted fever group |
| Species: | R. parkeri |
| Binomial name | |
| Rickettsia parkeri Lackmanet al., 1965 | |
Rickettsia parkeri (abbreviatedR. parkeri) is agram-negative intracellular bacterium. The organism is found in theWestern Hemisphere and is transmitted via the bite ofhard ticks of the genusAmblyomma.R. parkeri causes mildspotted fever disease in humans, whose most common signs and symptoms are fever, aneschar at the site of tick attachment, rash, headache, and muscle aches.Doxycycline should be given after any tick bite especially those occurring on children.
R. parkeri is classified in the spotted fever group of the genusRickettsia.[1][2] Genetically, its close relatives includeR. africae,R. sibirica,R. conorii,R. rickettsii,R. peacockii, andR. honei.[1]
The organism has been isolated from numerous species of ticks in the genusAmblyomma:A. americanum in the United States;A. aureolatum in Brazil;A. maculatum in Mexico, Peru, and the United States;A. nodosum in Brazil;A. ovale in Brazil and Mexico;A. parvitarsum in Argentina and Chile;A. tigrinum in Argentina, Bolivia, Brazil, and Uruguay; andA. triste in Argentina, Brazil, the United States, and Uruguay.[2][3][4][5] Different ticks may carry differentstrains of the organism.R. parkeri sensu stricto ("in the strict sense") is found inA. maculatum andA. triste;R. parkeri strain NOD, inA. nodosum;R. parkeri strain Parvitarsum, inA. parvitarsum; andR. parkeri strain Atlantic rainforest, inA. aureolatum andA. ovale.[2]
The first report of a confirmed human case of infection withR. parkeri was published in 2004.[6][7] The person was infected in the state of Virginia in the United States.[6] Other confirmed or probable human cases have been reported to have acquired infection elsewhere in the United States (e.g., Arizona, Georgia, and Mississippi), as well as in Argentina, Brazil, Colombia, Mexico, and Uruguay.[8][9] Terms used to describe human infection withR. parkeri include "American boutonneuse fever" because of its similarity toboutonneuse fever caused byRickettsia conorii;[10] "American tick bite fever" because of its similarity toAfrican tick bite fever caused byRickettsia africae;[11] "Tidewater spotted fever," after theTidewater region in the eastern United States;[12] and "Rickettsia parkeririckettsiosis" or "R. parkeri rickettsiosis."[7][12]
Of all human cases documented in the medical literature, 87% were 18-64 years of age, and most cases were male.[8] Brazil, Argentina, and the United States accounted for the majority of cases in the medical literature.[8] In the United States, most of the 40 cases reported to theCenters for Disease Control and Prevention (CDC) as of 2016 became infected between the months of July and September.[13]: 5–6
The CDC recommendspolymerase chain reaction (PCR) of a biopsy or swab of an eschar, or PCR of a biopsy of a rash, for diagnosis ofR. parkeri infection.[13]: 27 In addition, indirectimmunofluorescence antibody (IFA) assays using paired acute and convalescent sera can be used.[13]: 27
A 2008 study compared 12R. parkeri cases with 208Rocky Mountain spotted fever cases caused byR. rickettsii.[7] Although bothR. parkeri andR. rickettsii caused fever, rash, myalgia, and headache,R. parkeri caused eschars andR. rickettsii did not.[7] Furthermore, the percentage of patients hospitalized was lower forR. parkeri than forR. rickettsii (33% vs 78%), andR. parkeri led to no deaths whileR. rickettsii led to death in 7% of cases.[7]
A 2021systematic review of 32 confirmed and 45 probable cases of human infection withR. parkeri determined that 94% of the confirmed cases had fever, 91% an eschar, 72% a rash, 56% headache, and 56%myalgia, with similar percentages among the probable cases.[8] The rash was most frequently described as papular or macular.[8] Among the confirmed and probable cases, the most common treatment was doxycycline, followed bytetracycline.[8] Although 9% of all the cases were hospitalized, there was a "100% rate of clinical recovery."[8]
In 1939, Ralph R. Parker, director of theRocky Mountain Laboratory, and others published a paper on "a rickettsia-like infectious agent."[7][14] The agent, found inAmblyomma maculatum ticks collected from cows in Texas, produced mild disease in guinea pigs.[7][14] In 1965, Lackman and others named the rickettsial organismR. parkeri after Parker.[2][15]
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