Pathogen that affects the fertility of the Australian seal

Crawling through seal poop on a remote Bass Strait island and wrestling with a seagull over the fresh placenta of an Australian seal (Arctocephalus pusillus doiferus) is just a normal day at the office for Brett Gardener.

He undergoes this to find out what is ailing these majestic marine mammals.

Australian seals have been showing signs of distress in recent decades, with reduced rates of pup production threatening their population. (Although a study published last week suggests that climate change may help seal fertility on Kanowna Island, south of Wilsons Headland, Victoria.)

Gardener, a PhD candidate at the University of Melbourne, is investigating how the disease may be affecting her ability to bear pups to term.

Exactly why seals are struggling to produce and rear such large numbers of pups has been difficult for researchers to pin down, but the impact of pathogens on the species’ fertility and abortion rate has not been investigated.

“That’s where I came in, I decided, well, I’m going to take a look and see if any of the common causes of miscarriage that we’re looking for in land mammals are present,” says Gardener.

Harmful pathogen found

Sea lion
Brett Gardener analyzing the placenta of an Australian seal in the Bass Strait Islands. Credit: Provided by the researcher

By analyzing the aborted fetuses and placentas of Australian seals on the Bass Strait Islands, Gardener found that the pathogen Coxiella burnetii was present in seal populations. This finding was recently published in Frontiers of Marine Science.

On land, Coxiella infects animals such as goats and cows, often causing miscarriage and birth defects. When humans breathe in dust contaminated with Coxiella, it can cause Q fever, which can be deadly.

“The only reports prior to this one of Coxiella [in marine mammals] was in the Northern Hemisphere, but it has been associated with declining marine mammal populations in the Northern Hemisphere,” says Gardener.

It seemed significant to him that the pathogen was found both in aborted fetuses and in placentas of live-born pups.

“Or they are producing premature offspring and are very weak and may have reduced survivability,” he says. “Or it could be that Coxiella is there and it’s not a pathogen like in terrestrial mammals.”

The Coxiella infecting these seals was subtly different from its terrestrial counterpart.

“Many of the markers we were looking for are not expressed in marine species,” says Gardener. “So a really good question is, is this a major cause of their population decline or is it really some organism that they’ve always had around?”

A smoking gun?

Seal specialist Mary-Anne Lea, professor of Ecology and Biodiversity at the Institute for Marine and Antarctic Studies (IMAS) in Hobart, agrees that unraveling the causes of the failure to produce pups is incredibly complex. Lea did not participate in the study.

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A day in the life: Brett Gardener collecting seal waste samples on the Bass Straight Islands. Credit: Researcher provided

Even in species like Steller’s sea lion (eumetopias jubatus), a well-studied northern hemisphere species that is known to carry Coxiella, it is difficult to determine whether the presence of the pathogen is a cause of the population decline.

Changes in prey base (food availability), pollutants, anthropogenic interaction such as bycatch, climate change, increased marine heat waves and extreme weather events such as storms can all affect the production of Australian seal pups, says Lea.

“If there are off-season storms that take the hatchlings off the island, that could have a direct impact on mortality.”

Another possibility is that a combination of stressors in the system could lead to “proper conditions for the expression of these pathogens,” she explains.

“Without regular screening and also population monitoring, where you’re studying known individuals and you get a sense of the frequency of these events [abortions] are for individuals, it’s very difficult to attribute an impact,” says Lea.

Gardener is up for the challenge of figuring out exactly what Coxiella’s impact on pup production: “This is going to be a lot more complicated because I’ll have to capture the females, determine if they’re pregnant and determine if they have Coxiella and then see if they produce a pup at a later date.” term.”

Can this virus affect humans?

Because the coxiella produced in seals is subtly different from what we are used to on land, it is unknown if it can enter humans and cause Q fever.

“We desperately need to find out if this is really a very risky pathogen or if it doesn’t have the massive virulence of terrestrial Coxiella,” says Gardener.

Given Gardener’s penchant for crawling through seal colonies, this is more than an academic matter for him; It’s personal: “There are a lot of people working in seal colonies in Australia and New Zealand and we’re all crawling through the dust, which is where these Coxiella stay in their environmentally resistant form.” Lea, in turn, emphasizes the link between human health and ecosystem health. “Humans are part of these ecosystems and we affect and are affected by them,” she says.

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