Rickettsia parkeri Infection
The genus Rickettsia is included in the bacterial tribe Rickettsiae, family Rickettsiaceae, order Rickettsiales. The genus Rickettsia includes many species of bacteria associated with important and severe human or canine disease, including those in the spotted fever group and in the typhus group. The typhus group (TG) is composed among others of R. prowazekii and R. typhi, which are associated with lice and fleas, respectively; the spotted fever group (SFG), which currently includes more than 20 valid species, is mostly associated with ticks. Other Rickettsia species have been classified in distinct groups or gathered as unclassified Rickettsia.
R. parkeri has first been isolated in 1937 as a distinct rickettsial strain from Gulf Coast ticks (Amblyomma maculatum), by Ralph Robinson Parker, showing low-grade fever and periorchitis in the animal experiment (here: male guinea pigs). In 1965, the “maculatum agent” was named R. parkeri and described as a small, rod-shaped bacterium, with an average size of 1.6 x 0.5 µm, found in the nucleus and cytoplasm of infected cells (Lackman et al., 1965). Until 2002 the agent most often was relegated to the group of ‘nonpathogenic’ SFG rickettsiae, found in ticks in the United States, when the first confirmed infection with R. parkeri in a human was identified in Virginia (Paddock et al., 2004).
- Lackman DB, Bell EJ, Stoenner HG, et al.: The Rocky Mountain spotted fever group of rickettsias. Health Lab Sci. 1965, 2, 135-41
- Paddock CD, Sumner JW, Comer JA, et al.: Rickettsia parkeri: a newly recognized cause of spotted fever rickettsiosis in the United States. Clin Infect Dis. 2004, 38, 805-11