Rickettsia honei: a spotted fever group Rickettsia on three continents

Abstract

Rickettsia honei (also known as strain TT-118) has been detected on three continents. Originally isolated in Thailand in 1962 (and confirmed in 2001), it has also been detected on Flinders Island (Australia) in 1993 and in Texas (USA) in 1998. On each continent it has been associated with a different species of tick. The original isolate (Thai Tick Typhus strain TT-118) was from a pool of larval Ixodes and Rhipicephalus ticks. Later it was detected in I. granulatus from Rattus rattus. Its pathogenicity for humans has not yet been confirmed in Thailand, but it is possibly responsible for the Spotted Fever Group human rickettsiosis in Thailand. The strain from Texas (USA) was isolated from Amblyomma cajennense ticks taken from cattle. Its pathogenicity for humans has not yet been confirmed in Texas. However, this tick is known to bite humans. The strain from Flinders Island (Australia) described as R. honei, has been isolated from patients with "Flinders Island Spotted Fever" and from Aponomma hydrosauri ticks taken from blue-tongue lizards (Tiliqua nigrolutea), tiger snakes (Notechis ater humphreysi), and copperhead snakes (Austrelaps superbus) on Flinders Island. The ecology of R. honei in this location is unusual in that reptiles, rather than mammals, are the vertebrate hosts.