Climate change leads to spread of phocine distemper virus in North Pacific
UC Davis researchers at the One Health Institute, in collaboration with other co-authoring institutions, have linked the loss of sea ice in the Arctic with the emergence of a deadly virus in marine mammals in the North Pacific, according to a study published on Nov. 7 in the journal “Scientific Reports.”
After phocine distemper virus (PDV) was identified in northern sea otters in Alaska in 2004, scientists wanted to know how this pathogen, that previously had only been found in the North Atlantic, reached the Pacific Ocean. Upon completing the 15-year study, the researchers discovered that the decline of sea ice in the Arctic has opened up new pathways to spread the pathogen between marine mammal species, according to Tracey Goldstein, the associate director of the One Health Institute at the UC Davis School of Veterinary Medicine and one of the principal investigators of the study.
“Sea otters aren’t migratory, so we wondered how viruses from the Atlantic got into animals in the Pacific and how it was introduced,” Goldstein said.
For this study, the One Health Institute brought together multidisciplinary teams to look at the intersection of human, environmental and animal health impacts of this pathogen in the Arctic, according to Jonna Mazet, the executive director of the One Health Institute and the other principal investigator of this study.
“Members of the marine mammal community all came together to work with us at UC Davis because we were concerned about the pathogen in the Arctic that didn’t belong in the Pacific Ocean,” Mazet said.
According to Mazet, PDV killed thousands of European harbor seals in the North Atlantic in 2002, so its recent emergence in the Pacific Ocean poses a serious threat to the mammals that live there.
“We are like disease detectives to find out why [PDV] is showing up in marine animals in an ocean that it should not be in,” Mazet said.
After pooling data from 2001–2016, researchers found a pattern that illustrates how melting sea ice allows marine mammals to move further into the Arctic and make contact with Pactific Ocean species. The 2002 outbreak in European harbor seals in the North Atlantic occurred in September, which is the time of year when ice is lowest. Also, 2002 was the first year the Arctic channel had an opening in the ice, Goldstein said
“Antibodies told us there had been exposure in 2003 in pups,” Goldstein said. “The moms might have been exposed earlier in 2002 or 2003.”
A second peak in an outbreak of the virus occurred in 2009, following the same pattern as the 2002 outbreak, since there was an opening in the Arctic ice again in 2008. Scientists believe infected marine mammals reintroduced PDV in the North Pacific, according to Goldstein.
“There is variability from year to year with how many [marine mammals] are injected, but there is evidence that there are long-term changes due to climate change,” said Elizabeth VanWormer, a postdoctoral researcher at UC Davis during the study and the first author in the paper. “Since 2008, the ice in the Arctic has been open almost every year, creating many more opportunities for diseases to be shared across oceans.”
Climate scientists have provided good evidence to link climate change to the reason for the decline in sea ice and the acceleration in the cycles of sea ice change, according to Mazet.
“This is direct evidence that there are health threats due to the climate crisis,” Mazet said. “Climate critics will point to how they think it’s going to take decades to know if [climate change] is true, but this study shows it is true. These animals are giving us a very clear warning sign to do something now.”
The marine mammals that were researched in the study include Steller sea lions, northern sea otters, northern fur seals, spotted seals, gray seals, harbor seals, harp seals, ribbon seals, bearded seals, ribbon seals and ring seals, VanWormer said.
“We studied pretty diverse populations over time, which helped us understand how the virus was moving among populations,” VanWormer said.
Researchers found that each mammal reacted differently to the disease, some more negatively than others.
“Harbor seals are very susceptible to disease, and they get sick and die,” Goldstein said. “Gray seals don’t always get very sick and share the disease. Harp seal are carriers and give it to other animals in the Arctic. Sea lions and northern fur seals, ribbon seals, ring seals, spotted seals and sea otters can all be infected but we are not sure [about] all of the effects [they experience].”
After conducting this research, Goldstein said the pathogen is more widespread than previously thought and can infect many different animals. Since the Arctic ice has been open almost every year since 2008, diseases can spread more easily.
“As the environment changes, it affects animal health and affects human health,” Goldstein said. “It is all linked and holistically affect each other.”
Researchers were concerned that the pathogen could harm people who live in the Arctic and hunt marine mammals through traditional practices. No evidence has shown the pathogen causes harm to humans, Mazet said, but it can impact the people who depend on marine mammals in other ways.
“Up in the Arctic, for Native Alaskans, these animals are really important for people,” Goldstein said. “As animals are affected, people are affected as well. People, animals and the environment are all very connected. Climate change increases the effects on the livelihood of the people in the Arctic.”
In addition to UC Davis’ contributions, other co-authoring institutions include the University of Saint Andrews, U.S. Fish and Wildlife Service, National Marine Fisheries Service (NOAA Fisheries), Alaska Fisheries Science Center’s Marine Mammal Laboratory, University of Glasgow, Alaska Department of Fish and Game, University of Alaska-Fairbanks, Queen’s University Belfast, Pirbright Institute and Alaska Veterinary Pathology Service.
“By collaborating with one another, we could pool data together,” Mazet said.
Funding for the study was granted by the Morris Animal Foundation, NOAA Oceans and Human Health Graduate Traineeship Program, the Alaska Fisheries Science Center Marine Mammal Laboratory and the U.S. Fish and Wildlife Service.
Because of the high impact of this study on animals, humans and the environment, the Morris Animal Foundation (MAF) granted the study a total of $70,152 between August 2009 to October 2012, according to Kelly Diehl, the senior director of science and communications at the MAF. The foundation understands how wildlife can have great effects on the rest of the world.
“I’m really proud of [the] foundation for dipping their toe in this controversial topic, and for not being afraid to fund it,” Diehl said. “If the science is solid, we want to fund it. It is important to do solid science that adds to conversation when a topic is controversial.”
Even though their paper has already been published, researchers are continuing their work on this topic. The published study contains samples through 2016, so now scientists are studying samples collected from the last two years to assess the virus’ current status in the Arctic, Goldstein said.
“We want to continue to monitor this,” Goldstein said. “In the Atlantic ocean, we see cycles of the virus peaking between five to 10 years, but in the Pacitifc we see there are different peaks. We want to know the next time [an outbreak] happens and if any deaths happen.”
Written by: Margo Rosenbaum — science@theaggie.org
