We recently diagnosed rickettsial spotted fever in four patients from the south-eastern coastal region of South Australia near Adelaide, an area not known to be endemic for this infection. All infections were acquired within the geographic range of Aponomma hydrosauri, the tick vector of Rickettsia honei. Infection by R. honei was confirmed in two patients. This extension of the known geographic range of R. honei infection may be explained, in part, by alterations in host–parasite ecology.
Two spotted fever group (SFG) rickettsia species endemic to Australia are known human pathogens — Rickettsia australis and Rickettsia honei.1 R. australis, the agent of Queensland tick typhus (QTT), is transmitted by ticks of the genus Ixodes, principally I. holocyclus,2,3 and has been associated with infections along the eastern seaboard from tropical north Queensland to Wilsons Promontory, in Victoria. The hosts for these tick vectors are mammals, including native rats and bandicoots.2 Confirmed cases of R. honei infection, or Flinders Island spotted fever, have previously been described only on Flinders Island, in Bass Strait,4 although a rickettsial spotted fever illness, possibly caused by R. honei, has also recently been reported from the east coast of Tasmania.5 Recently published findings indicate that the parasitic tick Aponomma hydrosauri, which has a variety of reptile species as its hosts, may be the principal vector of R. honei.6
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