Sea otters and seals in the Pacific, off the coast of Alaska, are infected with a virus that was once only observed in animals in the Atlantic.
A new study suggests that ice melt in the Arctic may be to blame – and that climate change can help spread the disease to new areas and new animals.
Tracy Goldstein, a biologist at the University of California, Davis, became curious when Pacific otters tested positive for the Focin plague virus – a cousin of canine plague virus – in 2004, for two years after a major outbreak among European port seals.
Until 2002, the seas around the Arctic Circle remained largely frozen even in late summer. This year, however, the Arctic Ocean between the North Atlantic and the Pacific Ocean was passable in late summer, she and her colleagues found.
Although sea otters do not go far from home, seals could probably transmit the virus from the Atlantic to the Pacific, says Dr. Goldstein.
Sea ice melting is a possible explanation for the spread of viruses – but it is not the only one, said Charles Inis, veterinarian and director of animal health at the New England Aquarium in Boston.
"A skeptic may argue that this virus may be transmitted through an intermediate host, such as a bird that can fly long distances," says Dr. Inis, who did not participate in the new study. "Or maybe it is transmitted in ballast water by ships or something like that."
Even illegal trade in pets or wild animals or contaminated meat transported from one coast to another can spread the virus, he added.
Dr. Goldstein and her team also looked at antibodies against the virus in animals. There is no evidence of antibodies in tests conducted before 2000.
But in 2002, a new study found "quite a difference" in antibody levels in Steller's sea lions, Dr. Goldstein says, suggesting that animals have active infections or had recovered from them.
The fossin plague virus is quite deadly among the Atlantic seals of the seals. Hundreds of seals and gray seals were found dead in 2018 along the coast of New England, from Massachusetts to Maine due to plague and flu infections.
But harp seals appear to be more capable of surviving focal plague, Dr. Goldstein said, and may serve as his reservoir – the ecological niche in which the infection persists. Outbreaks can begin when a diseased harp contacts the gray seal . The outbreaks appear to come in cycles, Dr. Goldstein said, as the animals build immunity against the infection. Every five to 10 years, when new seals and otters are born and overall immunity weakens, the population becomes susceptible again and another outbreak occurs.
A new study identified a second wave of viral antibodies in 2009 in several types of seals, including ice seals, northern leather seals, and Steller sea lions. This study was completed in 2016, so it's not clear if the virus has spread since then, Dr. Goldstein said.
But she worries that another cycle of infection may not be far off. "These ice channels seem to open every year, so these rare events can become more frequent," she said.