|SHORT RESEARCH COMMUNICATION
|Year : 2018 | Volume
| Issue : 3 | Page : 239-241
Attempt to uncover reservoirs of human spotted fever rickettsiosis on the Fleurieu Peninsula, South Australia
Patrick L Taggart1, Rebecca Traub2, Sze Fui2, Phil Weinstein3
1 School of Animal and Veterinary Sciences, University of Adelaide, Adelaide, Australia
2 Faculty of Veterinary and Agricultural Sciences, University of Melbourne, Parkville, Australia
3 School of Biological Sciences, University of Adelaide, Adelaide, Australia
|Date of Submission||18-Feb-2018|
|Date of Acceptance||16-May-2018|
|Date of Web Publication||4-Jan-2019|
Patrick L Taggart
University of Adelaide, Veterinary Health Centre, Building E40, Mudla Wirra RD, Roseworthy, South Australia
Source of Support: None, Conflict of Interest: None
Keywords: Bothriocroton hydrosauri; Ixodes hirsti; Rickettsia honei; South Australia; spotted fever; vector
|How to cite this article:|
Taggart PL, Traub R, Fui S, Weinstein P. Attempt to uncover reservoirs of human spotted fever rickettsiosis on the Fleurieu Peninsula, South Australia. J Vector Borne Dis 2018;55:239-41
|How to cite this URL:|
Taggart PL, Traub R, Fui S, Weinstein P. Attempt to uncover reservoirs of human spotted fever rickettsiosis on the Fleurieu Peninsula, South Australia. J Vector Borne Dis [serial online] 2018 [cited 2020 Jan 22];55:239-41. Available from: http://www.jvbd.org/text.asp?2018/55/3/239/249483
During the years 2001–2003, multiple outbreaks of human spotted fever group rickettsioses occurred on the south coast of South Australia,. The causative agent of Flinders Island spotted fever, Rickettsia honei, identified in the reptile tick Bothriocroton hydrosauri, was implicated as the likely vector involved in these epidemics. Larvae, nymphs, and adults of B. hydrosauri infest reptiles almost exclusively. Very few reports exist documenting B. hydrosauri as an ectoparasite of mammals; in one report it was reported to parasitise a human and in another it was reported parasitising an ox.
Whilst the transmission of R. honei from B. hydrosauri to humans is possible through accidental parasitism of humans, multiple rickettsioses outbreaks transmitted by B. hydrosauri is unexpected based on current knowledge of its host range. With this in mind, the question arises, if R. honei could have reservoirs other than B. hydrosauri, as has been suggested by Unsworth et al. One potential reservoir and vector of R. honei could be the three-host tick Ixodes hirsti. Larvae and nymphs of I. hirsti parasitise birds in the same area where the documented human rickettsioses outbreaks occurred, with the adult life stages parasitising mammals. Whilst there are no documented reports of I. hirsti parasitising humans, it is expected that they are within its mammalian host range. Further, Rickettsiales spp have been identified in I. hirsti through the amplification and sequencing of the V4 region of the 16S rRNA gene, but are too short and conserved to allow differentiation of genera (unpublished data), and Ixodes ticks are documented vectors of human spotted fever group rickettsiosis within the Oceania region. This study aimed to determine, if I. hirsti is a potential reservoir of human spotted fever group rickettsiosis on the south coast of South Australia, by amplifying the citrate synthase (gltA) gene of spotted fever and typhus group Rickettsia spp in I. hirsti ticks.
Ticks were collected from 40 birds, mist-netted within the following South Australian conservation parks on the Fleurieu Peninsula: Newland Head (–35° 37′ 46.7394″; 138° 30′ 12.7758″); Cox Scrub (–35° 20′ 3.12″; 138° 43′ 59.8476″); Deep Creek (–35° 37′ 0.0114″; 138° 15′ 24.876″); Flinders Chase (–35° 57′ 6.192″; 136° 44′ 10.1868″); Vivonne Bay (–35° 57′ 6.192″; 136° 44′ 10.1868″); and Pelican Lagoon (–35° 48′ 16.7574″; 137° 46′ 46.6638″) [Figure 1]. All ticks were preserved in 90% ethanol.
|Figure 1: (a) Location of the Fleurieu Peninsula (box) in South Australia; and (b) Location of the conservation parks (black dots) where tick samples were collected within the study region. FC— Flinders Chase; VB—Vivonne Bay; PL—Pelican Lagoon; DC—Deep Creek; NH—Newland Head; and CS—Cox Scrub.|
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DNA was extracted from crushed ticks using a DNeasy blood and Tissue kit (QIAGEN, Chadstone Centre, Victoria, Australia) following the manufacturer's instructions. A diagnostic TaqMan probe real-time PCR assay targeting the gltA gene of spotted fever and typhus group rickettsia was used for the detection of Rickettsia spp with modifications according to Hii et al. Reactions were performed in duplicate in a total volume of 10 μl containing KAPA Probe Fast qPCR mastermix (KAPA Biosystems, Wilmington, Massachusetts, United States), 400 nM of each forward and reverse primer, 200 nM of probe and 2 μl of extracted DNA. For each run, a negative control of sterile PCR-grade water and a positive control of cultured R. honei was included in the real-time PCR assay. The reactions were run, detected and analysed on a Rotor-Gene 126.96.36.199. (QIAGEN, Chadstone Centre, Victoria, Australia).
DNA from 40 Rickettsiales-positive I. hirsti ticks were screened for spotted fever and typhus group rickettsiae by the real-time PCR. No samples returned a positive for Rickettsia spp (both spotted fever and typhus group). The specific real-time PCR is capable of amplifying all spotted fever and typhus group riskettsiae, except the ancestral group rickettsia, R. bellii, and all other members of the order Rickettsiales. It is, therefore, suggested that the Rickettsiales originally detected in the microbiome study of I. hirsti in Australia are likely to be a common endosymbiont of Ixodes spp, such as Candidatus midichloria mitochondrii (CMM), and not Rickettsia spp, due to the CMM's ubiquitous nature in Ixodid ticks.
The vector of human rickettsiosis outbreaks on the Fleurieu Peninsula, South Australia must be assumed to be B. hydrosauri until proven otherwise. However, a recent survey of B. hydrosauri collected from the lizard Tiliqua rugosa in close proximity to the Fleurieu Peninsula, failed to detect R. honei. Instead, 100% of the ticks harboured an uncharacterised Rickettsia sp. The ability of B. hydrosauri to potentially harbour R. honei at a high prevalence, as it does for other Rickettsia spp, increases its probability of transmission to humans, despite infrequent report of it parasitising mammalian hosts,. Surprisingly, R. honei was neither detected by PCR nor by cell culture in the blood of three reptile species (T. nigrolutea, Austrelaps sepurbus and Notechis scutatus).
Rickettsia honei has been isolated from a range of tick genera in addition to Bothriocroton, including Haemaphyalis from humans, Ixodes from black rats (Rattus rattus) and Amblyomma from cattle. Hence, potential candidate vectors of human rickettsiosis infection on the Fleurieu Peninsula/south coast of South Australia may include other ticks associated with the parasitisation of mammals. It is important to identify such potential vectors of human rickettsiosis for effective management and proper understanding of the disease risk. Further investigation is required to identify tick species commonly parasitising mammals in the study area to ascertain their ability in harbouring and transmitting spotted fever and typhus group Rickettsiae.
Ethical issues/Conflict of interest
The authors declare no conflict of interest or ethical issues.
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