Rickettsiales and rickettsial diseases in Australia - Murdoch ...

the surrounding extra-vascular space 269 . Although rickettsial infection can affect
every organ, the organism does not commonly spread beyond the vascular and
lymphatic systems 268 .
As with Anaplasma and Ehrlichia, Rickettsia are transmitted by an arthropod
vector, primarily ticks, although unlike Anaplasma and Ehrlichia, ticks typically
act as both vector and reservoir for rickettsiae. Tick species from the genus
Amblyomma 137 , Bothriocroton (formally Aponomma) 237 , Haemaphysalis 137 ,
Dermacentor 157, 164 , Rhipicephalus 254 , Ixodes 41 and Argas 188 have all been
associated with rickettsial species. Chigger mites (Leptotrombidium
deliense) 254 , fleas (Ctenocephalides spp.) 195, 221 and lice (primarily Pediculus
humanus) 158 have been recorded as vectors of various rickettsial species.
1.2.2.2. Orientia
Like all Rickettsiales, Orientia are obligate intracellular organisms. They are rod
shaped cells approximately 1.2 to 3.0µm in length and 0.5µm in width 271 and
until recently were considered to be a species of Rickettsia 244 .
The genus currently contains only the single species Orientia tsutsugamushi,
although the species is broken into several serotypes including the three
original serotypes; Kato, Karp and Gilliam 271 .
As with Rickettsia, the primary site of infection is the vascular endothelial
cells 159 , but, Orientia can also infect leukocytes 210 including monocytes and
macrophages 43 . As with rickettsial disease, Orientia infection causes an
increase in vascular permeability due to damage to the vascular endothelial
cells, resulting in an increase in extra-vascular fluid and subsequently
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