The Family Borreliaceae in Australia: Diversity, Tick Vectors, Wildlife Hosts and the Lyme Disease Controversy

The family Borreliaceae comprises the genera Cristispira and Borrelia, the latter including the subgenera Borrelia and Borreliella. Australia hosts a unique assemblage of wildlife and tick species that may support the circulation of indigenous Borrelia lineages. A narrative review of the available literature was conducted to summarize current knowledge of the taxonomy, diversity, ecology, tick associations, vertebrate hosts, and potential public health significance of Borreliaceae detected in Australia. The diversity of Australian Borrelia is currently represented by members of the relapsing fever (RF) and Echidna-Reptile (REP) groups. These include Borrelia queenslandica, Borrelia sp. HB, Candidatus Borrelia tachyglossi, Ca. B. undatumii, and Ca. B. rubricentralis, which have been detected in association with native wildlife and tick species. However, vector competence has not yet been demonstrated for most tick-associated Borrelia lineages identified in Australia. To date, no indigenous member of the Borrelia burgdorferi sensu lato complex has been convincingly detected in Australian ticks, wildlife, or humans. Nevertheless, persistent symptom complexes following tick exposure have been reported and are currently grouped under the umbrella term Debilitating Symptom Complexes Attributed to Ticks (DSCATT). Current evidence indicates that Australian Borreliaceae fauna is dominated by indigenous relapsing fever and reptile-associated lineages rather than Lyme borreliosis agents. Further genomic, ecological, reservoir-host, and vector-competence studies are needed to clarify their transmission cycles, evolutionary relationships, zoonotic potential, and their significance within a One Health framework.