With all the preparations being made to help human populations get through Covid-19, many are wondering about the effect the coronavirus or similar viruses may have on our animal counterparts. Some panicky pet owners are even rushing to get their dogs special Covid masks.
While it’s highly unlikely your dog will catch Covid-19, SARS-type viruses do infect more animals than just humans, and there are plenty of other viruses that preferentially infect everything from birds, to whales, to plants.
In the Arctic, where melting sea-ice is opening up new territory for all lifeforms, scientists are seeing marine viruses act in new and concerning ways.
Phocine distemper virus (PDV), a pathogen that causes respiratory and neurological issues in seals and is related to Canine distemper virus, has caused mass die-offs in European harbour seals in the North Atlantic since at least the 1980s. Also present in Arctic seal populations, including Harp and Grey seals, PDV seems to exist in a few different strains around the Atlantic but is markedly more deadly for the southerly Harbour Seals.
It’s not uncommon for the occasional viral epidemic to kill off a large number of animals. Related species (or even populations of a single species) that overlap in range may routinely exchange viral infections. As long as enough infected animals survive, they’re likely to pass on whatever adaptive trait got them through the infection to the next generation – running a never-ending arms race with the virus’s own evolution. When a virus is novel to the population, though, mass mortality events like those seen in the Atlantic Harbour seals can occur.
PDV wasn’t found in the North Pacific until very recently. Scientists are now wondering if melting sea-ice is to blame for a rise in cases seen in Northern Sea Otters, found along the South-Western coast of Alaska.
Blood and Snot for Science
A collaborative study by American and UK researchers published in Nature last year compared known ranges for seal species, sea-ice records, and confirmed PDV cases to see what role the distemper virus may be playing in Pacific mortality events.
Bearded seals, Northern fur seals, and Stellar sea lions are all tagged and tracked by the Alaska Fisheries Science Centre’s Marine Mammal Laboratory, so the researchers were able to create accurate estimates of when and where the different species have overlapped through the years. This is important, because we know Northern Sea Otters didn’t get PDV from infected Harp or Grey Seals – they’re just too far apart from each other. Bearded seals, however, do share territory with other Arctic seals and are much more likely to have come in contact with infected species from the Atlantic.
From 2001-2016, the researchers routinely sampled the blood and swabbed the noses of the different seal species found from Alaska to Russia. The blood was used to search for PDV antibodies, something currently- or previously-infected seals would be producing to help their bodies fight the virus. The nose swab was used to test for the virus itself, by amplifying and sequencing the virus’ genetic material.
Signs of current or very recent PDV infection were found in all the monitored Phocid species, indicating that the 2004 Sea otter cases were not an isolated phenomenon. Crucially, they also found a significant relationship between the percentage of animals showing PVD infection and the state of the sea-ice. In years the sea-ice opened up enough to allow for trans-ocean travel across the Arctic, as much as 50+% of the approximately 2,700 Phocids tested positive for PDV.
So PDV has entered the Pacific. Scientists aren’t sure yet what the presence of the virus means for the health of native seals and their relatives in the Pacific, though they suspect it may have played a role in a 2004-2006 die-off event in Sea otters as well as in sporadic Stellar sea lion deaths. It’s possible that, as in the Arctic, PDV is able to exist within some species or populations without causing mass mortality, but the potential for outbreaks in sensitive southern species is worrying.
Open ocean is quickly becoming the new normal in the Arctic. New and extreme disease events may also become more common as we more forward into this warmer age and will carry important implications for the fate of marine species. In seals, which are key components of coastal ecosystems at all latitudes, the effects of die-off events will be felt throughout the marine food chain. We need to make sure our marine economies are ready to adapt.
VanWormer, E., Mazet, J.A.K., Hall, A. et al. Viral emergence in marine mammals in the North Pacific may be linked to Arctic sea ice reduction. Sci Rep 9, 15569 (2019). https://doi.org/10.1038/s41598-019-51699-4
Hi! I’m Rebecca Parker. I’m an ecologist and plant lover working in non-profit conservation in Nova Scotia Canada. I trained at Dalhousie and Ryerson University, where I completed a Masters in Environmental Science and Management. I like botany, wetlands, and wetland botany! On the sciencey side, I like to write about current topics in population and community ecology, but I’m also really interested in environmental outreach, how exposure to science and demographics affect environmental values and behaviours, and best practices for building community capacity in environmental stewardship. Check out my instagram for photos of the awesome nature I see through my work.