by Grace Riley
An exciting new research group has released a new paper reporting on Human tick-borne disease in Australia. The world renowned neuroinflammation scientist Professor Gilles Guillemin of Macquarie University is joined by Professor Eddie Holmes, a leading evolutionary biologist distinguished for his work on the emergence and evolution of viruses, and doctors Bernie Hudson and Richard Schloeffel. It's exciting because it’s the first time that we have seen medical practitioners with extensive clinical experience in tick-borne disease in Australia work with world leading scientists to address the gaps in our knowledge.
Their paper provides contemporary analysis of the ticks that are known to bite humans in Australia. While there are more species of ticks, already proven by Murdoch University researchers to harbour three types of Borrelia exclusive to Australia, it’s not yet proven that they bite humans.
The long list of diseases capable of being transmitted to humans from these ticks is frightening; Q fever, Queensland tick typhus, Flinders Island spotted fever, and Australian spotted fever, Babesiosis, Anaplasma spp., Bartonella spp., Burkholderia spp., Francisella spp.; and a range of potentially fatal viruses; Dera Ghazi Khan virus, tick-borne encephalitis virus, Lake Clarendon virus , Saumarez Reef virus, Upolu virus, Vinegar Hill virus. Add to those the reported diseases found in the Murdoch studies, Ehrlichia and Neoehrlichia.
With increasing numbers of Australians reporting serious illness following a tick bite, it is confounding as to why there is a lack of focus on this emerging issue.
The paper warns that an increased incidence of tick-borne infections might “be observed in the future due to changes in demography, climate change, and increase in travel and shipments and even migratory patterns of birds or other animals”. It also confirms “the exact incidence of tick-borne disease in Australia is unknown”. This impedes the development of strategies for tick control and for the prevention and management of tick-borne illness.
Contemporary data on human biting ticks, their evolution in Australia, their habitats and main hosts as reported in scientific literature are included in Table 1 of the report. It emphasises the influence of climatic patterns on the existence of hosts, tick survival rates and the associated increase in exposure risk for humans. Importantly, it underpins the critical need for a better understanding of the epidemiology of ticks, their hosts and their pathogens.
An Australian map plots the geographical distribution of ticks which echoes LDAA’s tick-bite data showing that few areas of Australia are free of tick-borne infections. Areas indicated in red (1/dots) show where tick-borne diseases are transmitted, and those in yellow (2/dots) in central parts of Australia, show areas of potential. (image credit)
There is an interesting discussion of the rising incidence of tick-borne illness in other countries and repeated calls for more focused research in Australia. While we are repeatedly told there is no Lyme disease in Australia, based on vast scientific absence of Borrelia burgdorferi sl, the authors rightly note that evidence is limited because there has been little research into the issue since 1994. The authors note that the research that has been conducted “revealed the presence of a new relapsing fever group Borrelia”, which has not yet been properly investigated for its potential to cause illness in humans.
Alarmingly the authors note that Arboviruses (arthropod-borne viruses) are also on the increase and present yet another public health concern. The paper introduces several viruses that have been isolated in Australian ticks and have infected people. Advances in metagenomic sequencing technology offers an effective way of screening for these viruses, but this too relies upon a coordinated public health response and urgent funding.
As well as pathogen transmission and the potential infectious diseases, the paper highlights the growing, allergic, inflammatory and autoimmune illnesses attributed to tick bites.
The authors urge us to re-examine our perceptions of tick-borne illness using new laboratory and epidemiological tools, so we gain a better understanding of the role that tick-borne pathogens play in the communicable disease burden in Australia. As shown in the distribution map, tick-borne pathogens exist in most of the country, yet we still know very little about the associated potential for human disease and the consequential risks to public health.
A special thanks to the lead authors, both microbiologists, Mona Dehhaghi, Macquarie University and Hamed Kazemi Shariat Panahi, University of Tehran. We are grateful to the broadening groups of researchers who continue to search for answers to this conundrum and who use the best of their scientific knowledge in that quest.