Rickettsia akari, the etiological cause of rickettsialpox, was first described in 1946 in an outbreak among residents living within a cluster of apartments in New York City. The investigation of this and subsequent outbreaks in large population centers of the northeastern United States found the source to be house mice carrying infected mites. Recent studies have found similar sources, rodents carrying infected mites, associated with outbreaks in the Ukraine, Croatia and in the southern United States.
Rickettsia akari stains weakly and appears as small dots when using anti-SFG LPS sera, but appears bright and fully coccobacillary when using monoclonals specific for R. akari OmpB. LPS appears to comprise less of the s-layer than is found in most other SFG species, hence ELISA titers against purified OmpB protein are far more sensitive than titers against LPS and may be missed in IFA screens using substrates like R. rickettsii or R. conorii.