Ultrastructural and Genetic Evidence of a Reptilian Tick, Aponomma hydrosauri, as a Host of Rickettsia honei in Australia

Abstract

In 1993, a novel rickettsia was isolated from the blood of inhabitants of Flinders Island, Australia, with acute febrile illnesses. This rickettsia was found to be a new species of spotted fever group (SFG) rickettsia, eventually named Rickettsia honei. The suspected ectoparasite vector of this rickettsia has yet to be identified. The purpose of this study was to evaluate the presence of this rickettsial species in a suspected tick vector, Aponomma hydrosauri, by DNA sequencing and electron microscopy (EM). Ticks collected from an Australian blue-tongued lizard on Flinders Island and a copperhead snake in Tasmania were demonstrated to be infected with R. honei by PCR, DNA sequencing, and EM. Rickettsiae were found in ultrathin sections of salivary glands, malpighian tubules, and midgut epithelial cells. In a previous study with a R. honei-infected tick from Flinders Island, rickettsiae were found in the nuclei of midgut epithelial cells, and EM also revealed the presence of rickettsiae in the cytosol of oocytes and immature eggs, suggesting transovarial transmission. These results implicate A. hydrosauri as a possible host of R. honei on Flinders Island and Tasmania and also provide evidence favoring transovarial maintenance of R. honei.

Tick-Borne Rickettsioses around the World: Emerging Diseases Challenging Old Concepts

“…In 1995, a similar rickettsiosis emerged in Tasmania, where patients were found by PCR to be infected with R. honei (70). A. hydrosauri ticks removed from a Tasmanian were also positive by PCR, and recent work suggested again that transovarial transmission may occur in ticks (362). However, the definitive implication of A. hydrosauri as a vector and possibly reservoir of R. honei, requires further study.…”

“…Six were I. tasmanii (the main tick that bites humans on Flinders Island) and 2 were A. hydrosauri. Further, 29/46 (63%) of A. hydrosauri removed from 12 Australian bluetongued lizard on Flinders Island were shown to harbor R. honei by molecular techniques (128,362). DNA of R. honei has been detected by PCR in eggs obtained from engorged female ticks of this species, suggesting transovarial transmission of R. honei in the acarine host (128).…”

Tick- and flea-borne rickettsial emerging zoonoses

“…Between 1984 and 2004, nine more species or subspecies of tick-borne spotted fever rickettsiae were identified as emerging pathogens throughout the world, including, R. japonica in Japan [6,46,65,71,72,[82][83][84]146]; "R. conorii caspia" in Astrakhan [35,38,39,143], Africa [47] and Kosovo [48]; R. africae in sub-Saharan Africa and the West Indies [62,63]; R. honei in the Flinders Island, offshore of Australia [9,57,140,141], the Island of Tasmania, Australia [153], Thailand [73], and possibly in the USA [13]; R. slovaca in Europe [29,74,101,122]; "R. sibirica mongolotimonae" in China [157], Europe [44,118] and Africa [106,113]; R. heilongjiangensis in China [42,49]; R. aeschlimannii in Africa [11,112,121] and Europe [43]; and finally R. parkeri in the USA [104]. R. helvetica is also suspected to be a human pathogen in Europe [45] and Asia [46,61,107], but this needs c...…”

Rickettsiasp. inIxodes granulatusTicks,Japan

“…Samples were stored on ice until shipment to the California Department of Health Services' Viral and Rickettsial Disease Laboratory for processing. P. maniculatus serum samples were examined for immunoglobulin (Ig) G antibodies to the SNV nucleocapsid protein by ELISA with Centers for Disease Control and Prevention reagents (5).…”