Rickettsiae are strict intracellular bacteria requiring a host cell to replicate. Within the genus Rickettsia three groups are differentiated, one of which is the spotted fever group (SFG), of which members are associated mainly with ticks, but also with fleas and mites (Raoult and Roux, 1997). Within the SFG, Rickettsia parkeri is an emerging human pathogen, for which the dog has an important sentinel function. It is an agent of tick-borne rickettsiosis in the Americas which has also been named American Boutonneuse fever (Goddard, 2004; Goddard and Varela-Stokes, 2009) or Tidewater spotted fever (Wright et al., 2011).


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 animal disease, including those in the spotted fever group (SFG).

Rickettsia parkeri, as one species of this group, 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 ‘non-pathogenic’ 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).




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