Crawling through seal poo on a remote island in Bass Strait and battling a seagull for the fresh placenta of an Australian fur seal (Arctocephalus pusillus doriferus) is just an ordinary day at the office for Brett Gardener.
He sets out to find out what these majestic marine mammals are suffering from.
Australian fur seals have shown signs of distress in recent decades, with reduced pup production rates threatening their population. (Although a study published last week suggests that climate change could be contributing to the fertility of seals on Kanowna Island, just south of Wilsons Promontory, Victoria.)
Gardener, a PhD student at the University of Melbourne, is studying how the disease can impact their ability to carry puppies to term.
It has been difficult for researchers to pinpoint exactly why fur seals struggle to produce and raise large numbers of young, but the impact of pathogens on the species’ fertility and abortion rate n has not been studied.
“That’s where I came in, I decided, well, I’m going to look and see if any of the common causes of abortion that we look for in land mammals are present,” Gardener says.
Pernicious pathogen discovered
By analyzing the fetuses and aborted placentas of Australian fur seals on the Bass Strait Islands, the gardener discovered that the pathogen Coxiella burnetii was present in seal populations. This finding was recently published in Marine Science Frontiers.
On land, Coxiella infects animals such as goats and cows, often causing abortions and birth defects. When humans breathe in dust contaminated with Coxiella, it can cause Q fever, which can be fatal.
“The only reports prior to that of Coxiella [in marine mammals] was in the Northern Hemisphere, but it has been associated with declining populations of marine mammals in the Northern Hemisphere,” says Gardener.
It seemed significant to him that the pathogen was found both in aborted fetuses and in the placentas of live-born puppies.
“Either they produce puppies prematurely and they are quite weak and may have reduced survivability,” he says. “Or it could be that the Coxiella is there and it’s not a pathogen like it is in land 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 this actually an organism that they’ve always had around?”
A smoking gun?
Seal expert Mary-Anne Lea, a professor of ecology and biodiversity at the Institute for Marine and Antarctic Studies (IMAS) in Hobart, agrees that disentangling the causes of failing seal pup production is incredibly complex. . Léa did not participate in the study.
Even in species like the Steller sea lion (Eumetopias jubatus), a well-studied northern hemisphere struggling species known to carry Coxiella, it is difficult to determine whether the presence of the pathogen is a cause of the population decline.
Changes in the prey base (food availability), pollutants, anthropogenic interactions such as bycatch, climate change, increased marine heat waves, and extreme weather events such as storm surges could all have an impact on the production of Australian fur seal pups, says Lea.
“If there are unseasonal storm surges that wash the pups off the island, that can have a direct impact on mortality.”
Another possibility is that a combination of stressors in the system could lead to “conditions conducive to the expression of these pathogens,” she explains.
“Without regular screening or population monitoring, where you study known individuals and you get an idea of how often these events occur [abortions] are for individuals, it’s really hard to attribute impact,” says Lea.
Gardener is up for the challenge of figuring out what impact Coxiella might have on pup production: “It’s going to be a lot more complicated because I’m going to have to capture females, determine if they’re pregnant, and then determine if they have Coxiella. and then see if they produce a full-term puppy.
Could this virus have an impact on humans?
Because Coxiella brewing in seals is subtly different from what we’re used to on land, it’s unclear whether it could spread to humans and cause Q fever.
“We really desperately need to know if this is actually a very dangerous 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 in the dust, where these Coxiella lie 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 them and are affected by them,” she says.