0

Pathogen affecting the fertility of the Australian fur seal

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

He puts himself through this to find out what’s wrong with these majestic marine mammals.

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 may help the fertility of seals on Kanowna Island, just south of Wilsons Promontory, Victoria.)

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

Exactly why fur seals are struggling to produce and raise 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’ll take a look and see if any of the common causes of abortion that we would look for in terrestrial mammals are present,” says Gardener.

Pernicious pathogen found

Sealskin
Brett Gardener analyzing the placenta of an Australian fur seal in the Bass Strait Islands. Credit: provided by researcher

By analyzing the aborted fetuses and placentas of Australian fur 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 miscarriages and birth defects. When humans breathe in dust contaminated with Coxiella, they can cause Q fever, which can be fatal.

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

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

“Or they are producing premature pups and they are quite weak and may have less survivability,” he says. “Or it could be that Coxiella is there and not a pathogen like it is in terrestrial mammals.”

The Coxiella that infected 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 very good question is, is this one of the main causes of their population decline or is this actually an organism that they’ve always had around?”

A smoking gun?

Seal expert Mary-Anne Lea, Professor of Ecology and Biodiversity at the Institute for Marine and Antarctic Studies (IMAS) in Hobart, agrees that figuring out the causes of faltering pup production is incredibly complex. Lea was not involved in the study.

Sealskin
A day in the life: Brett Gardener collecting samples of fur seal waste in the Bass Straight Islands. Credit: provided by researcher

Even in species like the Steller sea lion (Eumetopias jubatus), a well-studied distressed northern hemisphere species known to carry Coxiella, it is difficult to determine whether the presence of the pathogen is the 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 storm surges could all be affecting 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 “ripe conditions for the expression of those pathogens,” he explains.

“Without regular assessment and also population monitoring, where you’re studying known individuals and you have an idea of ​​how frequent these events are [abortions] they’re for individuals, it’s really hard to attribute an impact,” says Lea.

Gardener is up for the challenge of figuring out what the impact of Coxiella might be on pup production: “That’s going to be a lot more complicated because I’m going to have to go and capture females, determine if they’re pregnant, and then determine if they have Coxiella and then see if they produce a full-term pup.”

Could this virus affect humans?

Because the Coxiella that brews in seals is subtly different than what we’re used to on land, it’s not known if it could jump to humans and cause Q fever.

“We really desperately need to find out if this is really a very risky pathogen or if it lacks the massive virulence of Coxiella terrestrial,” says Gardener.

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