Abstract
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.
Highlights
The number and diversity of human arthropod-borne infections following tick bites are second only to those following mosquito bites [1]
In Australia, a number of tick-borne diseases are endemic. These include Q fever caused by Coxiella burnetii, Queensland tick typhus caused by Rickettsia australis, Flinders Island spotted fever caused by R. honei, and Australian spotted fever caused by R. honei subsp marmionii [2,3,4]
Signed informed consent was obtained from all participants. Fourteen persons had their serum tested for antibodies to Rickettsia spp., C. burnetii, Orientia tsutsugamushi, Anaplasma spp., Ehrlichia spp., and Borrelia burgdorferi according to the standard serological diagnostic assays in use at the Australian Rickettsial Reference Laboratory (ARRL) in Geelong, Victoria, Australia
Summary
The number and diversity of human arthropod-borne infections following tick bites are second only to those following mosquito bites [1]. In Australia, a number of tick-borne diseases are endemic. The paralysis tick Ixodes holocyclus from central coast New South Wales has been shown to contain a number of potential human pathogens [5], but the risk of infection to persons who are bitten by this tick is not known. This is considered worthy of investigation as this tick commonly bites humans in eastern Australia. In this study staff from a companion animal contract research organisation (Wongaburra Research Centre, operated by VetX Research), located at Casino, in northeastern New South Wales and a group of associated tick collectors, were examined for antibodies to known tick-transmitted bacterial infections
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