Exploring Borrelia in Australia: Isolation, genomic characterisation, and host and vector associations

Area of Science:

• Microbiology
• Ecology
• Genomics

Background:

• Borrelia are tick-borne spirochetes causing Lyme borreliosis and relapsing fevers.
• Multiple Borrelia species exist in Australia, but their ecological roles and zoonotic potential require further investigation.
• Understanding Australian Borrelia diversity is crucial for public health and ecological assessments.

Purpose of the Study:

• To isolate and characterize two Australian Borrelia species: Borrelia tachyglossi and Borrelia sp. HB.
• To investigate the in vitro culture, genomic sequencing, and molecular prevalence of these species in ticks and wildlife hosts.
• To assess the zoonotic risk and ecological significance of Australian Borrelia.

Main Methods:

• In vitro cultivation of Borrelia species from ticks.
• Genomic sequencing of cultured Borrelia isolates.
• Molecular surveys of ticks and vertebrate hosts for Borrelia DNA.
• Complement-mediated bactericidal assays to assess pathogenicity.

Main Results:

• Borrelia tachyglossi was successfully cultured from Bothriocroton concolor ticks and fully sequenced; it demonstrated high susceptibility to human innate immunity.
• Borrelia sp. HB could not be cultured and showed very low prevalence (0.14%) in ticks, with no detection in 504 wildlife hosts, suggesting a cryptic cycle.
• Diverse reptile-associated Borrelia species were found in monitor lizards and snakes, supporting host-specific enzootic cycles.
• No evidence of Borrelia burgdorferi sensu lato was found; Australian Borrelia belong to relapsing fever and reptile-associated clades.

Conclusions:

• Borrelia tachyglossi is unlikely to be pathogenic to humans due to its susceptibility to innate immunity.
• Borrelia sp. HB appears to have a restricted or cryptic enzootic cycle in Australia.
• Australian Borrelia diversity is characterized by host-specific cycles, primarily involving reptiles and ticks, distinct from Lyme disease agents.
• Further research into Borrelia ecology, vector competence, and evolution in Australia is warranted.