Abstract
Coxiella burnetii is a well-known cause of abortion in domestic and wildlife species.1 Australia has one of the highest prevalence rates of human infections. Historically, it was associated with abattoir workers, but it recently has been shown that wildlife workers have a disproportionately high prevalence of infection.2 C. burnetii has been recorded from a small number of northern hemisphere marine mammals, potentially contributing to decreasing populations of northern fur seals (Callorhinus ursinus) and Steller sea lions (Eumetopias jubatus).3,4 Data around its disease ecology in marine mammals are sparse.3,5 Only recently, it has been described in marine mammals in the southern hemisphere from a single breeding colony of Australian fur seals (Arctocephalus pusillus doriferus) on Kanowna Island in Bass Strait.6
The Australian fur seal has experienced a slower-than-expected population recovery, with a high third-trimester abortion rate.7 Annual pup production has in recent years decreased for the biggest breeding colony for the species.8 Presently, it is suspected that C. burnetii is potentially a novel pathogen, contributing to decreased pup production in Australian fur seals. The aim of this study was to investigate the newly reported C. burnetii genotype through multiple modalities. Third-trimester abortions (n=53) were collected from two key breeding sites in southeastern Australia, Kanowna Island (KI) and Seal Rocks, and full-term placentas (n=120) from KI.
Three qPCR markers considered the “gold standard” for terrestrial Australian genotypes were used to screen samples (com1, htpAB, and IS1111[9]). A subset of samples (n=8) was additionally analyzed with a multiple-locus variation of tandem repeats analysis (MLVA) for loci ms-24, ms-28, and ms-33. Whole genome sequencing was performed on extracted DNA. Reads were aligned with the Coxiella burnetii Nine Mile genome. Both the com1 and htpAB markers showed noticeable levels of amplification. IS1111 amplification appeared to be absent. Only ms28 amplified on MLVA.
The IS1111 region could not be identified in the assembled genome using BLAST and CoxBase insertion sequence detector. Using the assembled genome in the CoxBase MLVA typing tool, a characteristic locus signature was detected with the presence of ms26, ms27, ms28, ms30, and ms31. Comparing the nucleotide identity between the Nine Mile reference strain and sequenced genome, more than 90% nucleotide identity was noted. It appears that the novel C. burnetii from Australian fur seals is a highly divergent genotype. Currently, there is no evidence of its presence in terrestrial species.
Six virulence factors were identified, and their presence that would elude pathogenicity might be similar to other C. burnetii genotypes (tadA, O-antigen, ompA, mceA, dotA, dotB). The presence of these virulence factors should potentially be considered a zoonotic risk.
Bass Strait is in one of the fastest warming oceanic regions, and marine mammals breeding in the area are key indicators of marine ecosystem stressors. This first description of C. burnetii in a marine mammal from the southern hemisphere illustrates some potential risks this pathogen poses to Australian fur seals and sympatric marine mammals. Additionally, it highlights the potential zoonotic risk of this pathogen.
Acknowledgments
This work would not have been possible without the great piloting skills of Sean Best and the brilliant skippering of the Victorian Fisheries Authority officers, who ensured that the field sites could be accessed despite difficult weather windows and ongoing COVID-19 restrictions. Our sincere thanks to Dr. Steven Graves for their ongoing support of our research. Research was conducted under the Department of Environment, Land, Water and Planning wildlife research permit 10009034/10009465.
*Presenting author
+Student presenter
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