Marine mammal conservationists warn of a contagious respiratory pathogen, cetacean morbillivirus (CeMV), that could potentially harm already endangered orca populations. Like the novel coronavirus SARS-CoV-2 that is causing the current COVID-19 pandemic, CeMV similarly has high transmission and mortality rates. With orcas being highly social animals, an outbreak could threaten entire pod populations, in turn drastically affecting the ecosystem, since orcas are apex predators.
According to National Geographic, more than a million cetaceans (whales, dolphins and porpoises) are eliminated each year through “bycatch [species caught unintentionally by fishermen], intentional killing, ship strikes, seismic surveys done for oil exploration, and naval sonar.” Oil spills are another risk, as are municipal and industrial waste polluting their marine environment. Chemicals accumulating in marine food chains are thereby ingested, leading to high toxicity levels that suppress cetacean immune systems.
Worryingly, Emerging Microbes & Infections journal affirms CeMV as the pathogen posing the greatest risk of triggering widespread disease in cetacean populations worldwide. What’s worse, CeMV is highly contagious, capable of spreading between cetacean populations of whales, dolphins and porpoises. Cases of CeMV first appeared in cetaceans during the 1980s. So far, Science Direct acknowledges at least six distinct strains of CeMV — porpoise morbillivirus (PMV), dolphin morbillivirus (DMV), pilot whale morbillivirus (PWMV) and beaked whale morbillivirus (BWMV).
Interestingly, Viruses journal states that CeMV is part of a virus family — the morbilliviruses — which includes the measles virus in humans and primates, the rinderpest virus in cattle, the peste des petits ruminants virus in goats and sheep, the canine distemper virus in dogs and the phocine distemper virus in seals and walruses.
Meanwhile, NOAA Fisheries estimates that of 50,000 orcas worldwide, about 2,500 reside “in the eastern North Pacific Ocean…[with] Southern Residents in the eastern North Pacific… listed as endangered in 2005.” This pocket of orcas has garnered media attention for their dwindling numbers as their primary food source, chinook salmon, is depleted. Human-induced noise also interferes with echolocation, threatening the orcas’ normal behavior. Additionally, lingering polychlorinated biphenyls (PCBs), despite being banned for decades, persist in the oceans, contaminating the food chain. As The Guardian revealed, “PCB concentrations found in killer whales can be 100 times safe levels and severely damage reproductive organs, cause cancer and damage the immune system.” Immuno-compromised orcas are left susceptible to pathogens like CeMV.
Researchers ran simulations to see what would happen should the highly infectious CeMV enter a pod population. Models indicated 90% of the population would succumb. Biologist Michael Weiss of San Juan Island’s Center for Whale Research explained in a Biological Conservation journal study, “The social structure of this population offers only limited protection from disease outbreaks.”
While immunization against measles in humans and canine distemper in pets has been successful, vaccines against CeMV for whales might not be deployed practically — unlike the morbillivirus vaccine program under development for endangered seals. A more viable solution may be to enhance the conservation of chinook salmon to minimize the chances of orca hunger and boost their immune systems.
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