Shrinking sea ice in the Arctic opens new pathways for animal disease

Climate change could be carving a path for dangerous diseases through the Arctic, allowing them to spread between species of susceptible marine mammals, according to a recent study.

Researchers have connected rises in the transmission of phocine distemper virus through seal, sea lion and otter populations to the loss of ice around the Arctic, reporting their work Nov. 7 in the journal Scientific Reports.

“As sea ice continues its melting trend, the opportunities for this virus and other pathogens to cross between North Atlantic and North Pacific marine mammals may become more common,” Elizabeth VanWormer, the study’s first author and an assistant professor at the University of Nebraska, Lincoln, said in a statement.

Scientists continue to grapple with understanding the knock-on effects of warmer waters lapping at the sea ice around the North Pole. They know that global sea levels will rise and that more ships in an increasingly ice-free Arctic could threaten vulnerable whale populations. Measurements of this repository of frozen seawater have indicated that 2019 had the second-lowest extent since we started using satellites to track sea ice levels 40 years ago.

VanWormer, who was formerly a postdoctoral researcher at the University of California, Davis, demonstrated with her colleagues that the ice may serve as a hurdle to disease transmission. Their research marshaled more than a decade and a half of data tabulating exposure to phocine distemper virus, or PDV, in several species of ice-dwelling seals and sea lions, as well as sea otters. Satellite-tag data from the species clued the researchers into their patterns of movement around the Arctic Circle.

PDV killed thousands of seals in the Atlantic Ocean in 2002, but didn’t turn up in Pacific marine mammal populations until 2004, when researchers found it in sea otters.

The team’s analysis allowed them to pinpoint spikes in infection rates, including one in 2003-2004 and another in 2009, when animals were more than nine times more likely to be infected than in typical years. Satellite imagery revealed that in the years before these peaks, the breadth of sea ice had bottomed out, opening up pathways for marine mammals to move.

“The loss of sea ice is leading marine wildlife to seek and forage in new habitats and removing that physical barrier, allowing for new pathways for them to move,” Tracey Goldstein, one of the paper’s authors and a professor at the UC Davis School of Veterinary Medicine, said in the statement. “As animals move and come in contact with other species, they carry opportunities to introduce and transmit new infectious disease, with potentially devastating impacts.”

The scientists write that the disease could have made its way from the Atlantic across the Northwest Territories in Canada, as different species moved through the once-ice-locked waters. That could have allowed a daisy chain of disease transmission from one species to the next where no pathway existed in the past.

The team’s genetic analyses of the collected virus strains, combined with the lack of sea ice in the Russian Arctic preceding the viral peaks, suggest that the virus may have instead — or also — slipped around the pole from the east.

“This study highlights the need to understand PDV transmission and the potential for outbreaks in sensitive species within this rapidly changing environment,” VanWormer said.

Banner image of an adult ribbon seal courtesy of NOAA Fisheries, Polar Ecosystems Program (Public domain).

Citation:

VanWormer, E., Mazet, J. A. K., Hall, A., Gill, V. A., Boveng, P. L., London, J. M., … Goldstein, T. (2019). Viral emergence in marine mammals in the North Pacific may be linked to Arctic sea ice reduction. Scientific Reports, 9(1), 15569. doi:10.1038/s41598-019-51699-4

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