Introduction
Tick-borne arboviruses pose a significant disease threat to humans and livestock 1,2. In addition to arboviruses, ticks also carry tick-specific viruses, some of which can affect their capacity to transmit arboviruses 3. The virome of Australian ticks remains largely unstudied 4, therefore comprising a kind of viral ‘dark matter’ that could influence future arbovirus outbreaks.
Methods
We collected 100 ticks from wild koalas at three bushland sites in Gold Coast, Queensland, and performed metagenomic sequencing for virus identification. Cox1 gene sequences were used to identify ticks.
Results and Discussion
The most abundant tick species was Ixodes holocyclus, followed by I. tasmani, and Haemaphysalis bancrofti. Using amino-acid sequences, we identified 13 viral taxa belonging to 5 families (Flaviviridae, Nairoviridae, Totiviridae, Rhabdoviridae, and Partitiviridae). These included three recently described tick-borne viruses: North Shore virus and Manly virus discovered in Sydney in 2019 4, and Newport tick virus (NTV) discovered in southern New South Wales in 2022 5. NTV belongs to the recently described Jingmenvirus clade of Flaviviruses, of which, some are zoonotic and cause disease in humans 6,7.
Our samples contained a high prevalence of bovine viral diarrhoea virus (BVDV). BVDV is considered the second-most significant disease affecting Australian beef cattle 8, but is not known to be transmitted by ticks, or to infect koalas. Therefore, the discovery of BVDV in koala-fed ticks is intriguing and could suggest a potential domestic-wildlife interface.
Further investigation is currently underway to obtain full-length viral genomes and perform phylogenetic analysis of the viruses mentioned above. Of particular importance are the putative NTV and the Nairovirus, due to the potential for these viruses to cause disease in humans. Additionally, serum from the koalas on which the BVDV-infected ticks were found will be used in a neutralisation assay to determine if BVDV can indeed infect koalas.