The microbiome and pathogenicity of Australian ticks are unique when compared to other species, and so is the response to ticks and tick-borne pathogens from native vertebrate hosts. While tick-borne bacteria have been relatively well studied in the northern hemisphere, very little is known about the presence or diversity of bacteria in Australian ticks. For example, it has become increasingly clear since the advancement of molecular barcoding techniques that many species of Rickettsia, Francisella, and Coxiella, which are generally considered pathogens of medical and veterinary importance, have evolved as non-pathogenic endosymbionts of ticks. The functional roles of tick microorganisms and their relationships may provide further insights into the pathogenicity and evolution of tick pathogens. Non-pathogenic microorganisms are typically transovarially transmitted and may impact tick growth, reproduction, fitness, nutritive adaptation and defence against environmental stresses. The effect of these organisms has been somewhat neglected in studies, but may present various detrimental, neutral, or beneficial effects to their tick hosts, and also contribute to driving the transmission of tick-borne pathogens. In addition to pathogens, the tick microbiome comprises a community of commensal and symbiotic obligate endosymbionts which make up the majority of the tick microbiome and reside both inside and outside the body of ticks. Ixodids transmit the widest number of pathogens worldwide and are responsible for the majority of tick-borne infections. However, ticks can transmit the widest range of pathogens of any arthropod vector and are the primary cause of vector-borne diseases in livestock and domestic animals. Each of the three families have evolved unique biological, physiological and ecological disparities which have resulted in different abilities and capacities to transmit pathogens. Ticks (Acari: Ixodidae) are obligate ectoparasitic arachnids that are classified into three families: Ixodidae (hard ticks), Argasidae (soft ticks), and Nuttalliellidae. The detection of various Proteobacteria in this study highlights the high bacterial diversity in native Australian ticks. Analysis of alpha-diversity showed high variability across both sample locations and instars, similar to previous studies. The most prevalent tick found on bare-nosed wombats was B. One adult male and two engorged adult female specimens were found on an adult male wombat from Coolagolite in New South Wales, and more specimens should be collected to confirm this host record. auruginans and a Rickettsiella endosymbiont dominated the bacterial profile for I. A species of Coxiella sharing closest sequence identity to Coxiella burnetii (99.07%), was detected in 72% of B. NGS results revealed the 16S rRNA gene diversity profile was predominantly Proteobacteria (55.1%) followed by Firmicutes (21.9%) and Actinobacteria (18.4%). The wombat tick was the most prevalent tick species comprising 94% of the total number of samples and was present on 97.9% (46/47) of wombat hosts. Tick infestations ranged from one to 73 ticks per wombat. Five species of ticks were identified comprising wombat tick Bothriocroton auruginans ( n = 420), wallaby tick Haemaphysalis bancrofti ( n = 8), bush tick Haemaphysalis longicornis ( n = 3), common marsupial tick Ixodes tasmani ( n = 12), and Australian paralysis tick Ixodes holocyclus ( n = 4). ResultsĪ total of 447 tick specimens were collected from 47 bare-nosed wombats between January 2019 and January 2020. Genomic DNA was extracted from a subsample, and following the amplification of the bacterial 16S rRNA gene V3–V4 hypervariable region, next-generation sequencing (NGS) on the Illumina MiSeq platform was used to assess the microbial composition. Wombat ticks were sourced from wildlife hospitals and sanctuaries across Australia and identified to species level using taxonomic keys. Little is known about the pathogens carried by most wombat ticks or how they may impact wombats and wombat handlers. Seven tick species are known to feed on bare-nosed wombats ( Vombatus ursinus), in addition to the highly prevalent Sarcoptes scabiei mite which causes fatal sarcoptic mange in most bare-nosed wombat populations. Ticks are obligate haematophagous ectoparasites of vertebrate hosts and transmit the widest range of pathogenic organisms of any arthropod vector.
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