Screening for Rickettsia, Coxiella and Borrelia Species in Ticks from Queensland, Australia.

Tick bites in Australia are linked to the transmission of a variety of infectious diseases in humans, livestock and wildlife. Despite this recognition, little is currently known about the variety of potential pathogens that are carried and transmitted by Australian ticks. In this study, we attempted to expand knowledge of Australian tick-borne bacterial pathogens by analyzing various tick species from the state of Queensland for potential human pathogens belonging to the Rickettsia, Coxiella and Borrelia genera. A total of 203 ticks, comprising of four genera and nine different tick species, were screened by specific qPCR assays. An overall Rickettsia qPCR positivity of 6.4% (13/203) was detected with rickettsial DNA found in four tick species (Ixodes holocyclus, I. tasmani, Amblyommatriguttatum, and Haemaphysalis longicornis). Amplification and analysis of several rickettsial genes from rickettsial qPCR positive samples identified sequences closely related to but genetically distinct from several previously described cultured and uncultured rickettsial species in the Rickettsia spotted fever subgroup. No ticks were positive for either Coxiella or Borrelia DNA. This work suggests that a further diversity of rickettsiae remain to be described in Australian ticks with the full importance of these bacteria to human and animal health yet to be elucidated.

An outbreak of scrub typhus in military personnel despite protocols for antibiotic prophylaxis: doxycycline resistance excluded by a quantitative PCR-based susceptibility assay.

Scrub typhus is caused by the obligate intracellular bacterium Orientia tsutsugamushi and is endemic to many countries in the Asia-Pacific region, including tropical Australia. We describe a recent large outbreak amongst military personnel in north Queensland. A total of 45 clinical cases were identified (36% of all potentially exposed individuals). This occurred despite existing military protocols stipulating the provision of doxycycline prophylaxis. Doxycycline resistance in O. tsutsugamushi has been described in South-East Asia, but not Australia. In one case, O. tsutsugamushi was cultured from eschar tissue and blood. Using quantitative real-time PCR to determine susceptibility to doxycycline for the outbreak strain, a minimum inhibitory concentration (MIC) of ≤0.04 µg/mL was found, indicating susceptibility to this agent. It seems most probable that failure to adhere to adequate prophylaxis over the duration of the military exercise accounted for the large number of cases encountered rather than doxycycline resistance.

Ixodes holocyclus Tick-Transmitted Human Pathogens in North-Eastern New South Wales, Australia.

A group of 14 persons who live in an area of Australia endemic for the Australian paralysis tick, Ixodes holocyclus, and who were involved in regularly collecting and handling these ticks, was examined for antibodies to tick-transmitted bacterial pathogens. Five (36%) had antibodies to Coxiella burnetii, the causative agent of Q fever and three (21%) had antibodies to spotted fever group (SFG) rickettsiae (Rickettsia spp). None had antibodies to Ehrlichia, Anaplasma, Orientia, or Borrelia (Lymedisease) suggesting that they had not been exposed to these bacteria. A total of 149 I. holocyclus ticks were examined for the citrate synthase (gltA) gene of the SFG rickettsiae and the com1 gene of C. burnetii; 23 (15.4%) ticks were positive for Rickettsia spp. and 8 (5.6%) positive for Coxiella spp. Sequencing of fragments of the gltA gene and the 17 kDa antigen gene from a selection of the ticks showed 99% and 100% homology, respectively, to Rickettsia australis, the bacterium causing Queenslandtick typhus. Thus, it appears that persons bitten by I. holocyclus in NE NSW, Australia have an approximate one in six risk of being infected with R. australis. Risks of Q fever were also high in this region but this may have been due to exposure by aerosol from the environment rather than by tick bite. A subset of 74 I. holocyclus ticks were further examined for DNA from Borrelia spp., Anaplasma spp. and Ehrlichia spp. but none was positive. Some of these recognised human bacterial pathogens associated with ticks may not be present in this Australian tick species from northeastern New South Wales.

Isolation of Coxiella burnetii from serum of patients with acute Q fever.

Worldwide there are few isolate collections of the intracellular bacterium Coxiella burnetii, due to the difficulties associated with working with the organism and the scarcity of suitable samples from which to attempt isolation. Particularly lacking are isolates from acute Q fever patients. The aim of this study was to evaluate whether the serum samples taken from patients with confirmed acute Q fever during the early stage of their disease represented a potential source of viable C. burnetii. Isolation was attempted from 65 of these samples by inoculation of the serum into Vero cell culture and was successful in 36 cases (55%). This high success rate was likely due to extended incubation of up to twelve weeks of the inoculated cultures, allowing the growth of the organism to levels detectable by PCR. Retrospective analysis of the time the sera was stored prior to inoculation into culture demonstrated that C. burnetii remained viable for 224 days in samples stored refrigerated and 371 days in samples stored frozen at -20 °C. These results demonstrate that standard serum samples taken from acute Q fever patients are a valuable source of new isolates of C. burnetii, with no special handling of the specimens required to maintain the organism's viability.