Abstract
The Australian fur seal (Arctocephalus pusillus doriferus) has experienced a slower than expected population recovery since the end of the commercial sealing era, with a high third trimester abortion rate. There is currently no known proximate cause. Coxiella burnetii (Cb) is a well-known cause of abortion in domestic and wildlife species and an important zoonotic pathogen. It has been recorded from a small number of northern hemisphere marine mammals and may be a potential contributory factor to decreasing populations of northern fur seals (Callorhinus ursinus) and Steller sealions (Eumetopias jubatus). It has not been recorded from marine mammals in the southern hemisphere but is well documented in ruminants and wildlife in Australia as a cause of reproductive failure. Third trimester aborted fetuses (n = 46) and full-term placentas (n = 66) from Australian fur seals, were collected on Kanowna Island and Seal Rocks in Bass Strait, south-eastern Australia. Utilizing routine hematoxylin and eosin histopathology, Cb immunohistochemistry and two different qPCR targets–htpAB and com1, Cb was identified. Routine histopathology and immunohistochemistry were insensitive for the detection of Cb. The detected Cb prevalence ranged from 10.6% for com1 up to 40.9% with htpAB. Coxiella burnetti was readily detected in full-term placentas but in aborted fetal material only in a single placenta associated with a still birth. The exact significance is currently unclear, but this highlights that Cb is present in Australian fur seals, breeding in Bass Strait. Bass Strait is in one of the world’s fastest warming oceanic regions and marine mammals breeding in the area are likely to be key indicators of marine ecosystem stressors. This first description of Cb in a marine mammal from the southern hemisphere, highlights the need to further investigate the potential risks this pathogen poses to Australian fur seals and sympatric marine mammals. Additionally, it is important to determine the zoonotic risk of this pathogen to persons working with, and in proximity of, Australian fur seal breeding colonies.
Highlights
There are many marine mammal populations that have recovered significantly since the shift toward conservation rather than exploitation
Of all the full-term placentas examined histologically on routine hematoxylin and eosin staining, intracytoplasmic bacteria were only detectable in one sample
With a detected Coxiella burnetii (Cb) prevalence ranging from 10.6 to 40.9%, this study brings to question what significance Cb holds for the reproductive ecology of Australian fur seals
Summary
There are many marine mammal populations that have recovered significantly since the shift toward conservation rather than exploitation. It was postulated that benthic foraging pinnipeds are faced with additional stressors (i.e., energetic expenditure and nutritional composition of benthic prey) that their pelagic foraging counterparts are not exposed to (Trites and Donnelly, 2003), potentially explaining the reduced recovery of certain pinnipeds (Rosen and Trites, 2005) This “nutritional stress hypothesis” was considered as potentially the reason for lower fecundity in benthic foragers such as the Steller sea lion (Eumetopias jubatus), Australian sea lion (Neophoca cinerea), and the Australian fur seal (Costa and Gales, 2003; Trites and Donnelly, 2003; Gibbens et al, 2010). Recent studies of the critically endangered Galapagos sea lion (Zalophus wollebaeki) suggest, that benthic foraging modes are not necessarily less efficient than pelagic foraging (Blakeway et al, 2021) This raises the question as to what other factors could be having a significant impact on the ability of the species such as the Australian fur seal to fully recover their population?
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