Posted on Category:Marine Life

Deadly Virus Marked Avian Flu Outbreaks in Marine Mammals

Last June, the phones of Marine Mammals of Maine started ringing – a lot. People walking along the rugged coastline of Casco Bay, which stretches north and south of Portland, reported sick or dead seals. The end of spring and the beginning of summer, when the puppies leave on their own, are usually the busiest period at the rescue and rehabilitation center, but the volume of calls continued to increase. “We were dealing with three times the number of animals we would normally deal with,” says Lynda Doughty, the center’s executive director.

The behavior of a seal stood out. The animal, Doughty recalls, was “neurological” — his weight and general diet were good, but in addition to coughing and sneezing, he was shaking and seemed disoriented. The young man’s condition worsened rapidly, and Doughty’s thoughts turned to the numerous recent reports of wild birds — such as raptors and gulls – infected with a new strain of H5N1, a highly contagious avian flu. Fearing that whatever was getting sick from the rapidly declining seal would spread to the other seals that populated the center, she made the difficult decision to euthanize it. Then she called Wendy Puryear.

When Marine Mammals of Maine has a dead animal whose health-issue cannot be identified after a rough autopsy, it often sends tissue samples to Puryear, a molecular virologist at Tufts University whose recent research has focused on how avian influenza passes from birds to mammals, and then to other mammals. At the University’s Runstadler Laboratory, Puryear and his team performed PCR tests on samples taken from seal swabs. When they came back positive, the team spent the night in a federal laboratory for confirmation. “I had to be absolutely sure of the results before I sounded the alarm,” says Puryear, “because I was expecting all the big wheels that would be set in motion immediately.”

This was the first confirmed matter in the world of this last extremely virulent strain of H5N1 in marine mammals, and it would not be the last. By the end of July, more than 330 gray seals and gray seals had died from the virus— enough for the National Marine Fisheries Service to immediately declare an “unusual mortality event” for pinnipeds along the Maine coast. Over the next few months, it became clear that H5N1 was barely contained in North America. Infections in seals and sea lions have since been confirmed in Europe, Russia and South America. The most serious passed away occurred this winter in more than 3,000 sea lions in Peru.

Avian influenza viruses are classified as weakly or highly pathogenic depending on their mortality for poultry, and some “low-pathway” strains can mutate into “high-pathway” influenza. The current variant of H5N1 is one of the most virulent high-route avian influenza ever documented, according to experts. It originated from breeding geese in Guangdong, China, in 1996 and, until 2005, wild birds spread the virus in Africa, the Middle East and Europe.

Last year, Puryear co-authored a study led by Nichola Hill, a biologist at the University of Massachusetts Boston, which examined how migratory seabirds, such as gulls, played an important role in the spread of H5N1. During a briefing with reporters last month, Hill noted that the first evidence took place in Newfoundland in December 2021, when a large black-backed gull and poultry were infected on a non-commercial farm around the same time. The health-issue has since finished nearly 59 million poultry and 6,715 wild birds in the United States, including endangered species such as the sand hill crane and the California condor. According to Hill, estimates of global wild bird mortality range from 10,000 to one Million individuals.

Only a year after the Guangdong epidemic in 1996, H5N1 reached Hong Kong, where it was detected for the first time in humans: 18 people were infected and six died. Although there have only been 890 human matters since the outbreak in Hong Kong, the virus has a mortality rate of 50%, according to the Centers for health-issue Control. What prevented H5N1 from infecting more people is that it does not seem to spread between mammals: it only moved from bird to mammal through direct contact with body fluids or feathers. But this new variant turned out to be different. When it passed through a mink farm in Spain last October, triggering the euthanasia of the facility’s 50,000 animals, the question of whether H5N1 could spread between mammals was resolved. “I think a big looming question for many of us is, “Do these recent outbreaks represent a new era for bird flu?”” Hill said at the Briefing. “And the answer is yes.”

Puryear and Hill are part of a group of scientists and researchers from the Gulf of Maine region who have been observing the evolution of avian influenza infection in marine mammals since 2011, when the H3N8 variant finished 162 young harbor seals in Maine, New Hampshire and Massachusetts. In fact, there have been periodic outbreaks of avian influenza among seals in the Americas and Eurasia, dating back to at least 1972. It had been widely accepted that these were sealbird events or one-off “dead-end spills” that do not spread between mammals. But after the passed away in 2011, Puryear, Hill and other colleagues decided to test this hypothesis. Was the flu “also circulating in marine mammals?”Puryear asked.

To collect data on as many marine mammals as possible, the researchers partnered with NOAA’s marine mammal health and stranding response program, which includes a network of small rescue and rehabilitation centers. Working with Doughty and his team, Puryear was able to obtain fluid, tissue, or swab samples from every reported seal stranding in Maine, both living and expired. These data, combined with those compiled from three-year visits to gray seal colonies where health assessments were carried out on more than 300 animals, allowed the researchers to determine that—at least in gray seals-infection with low-risk avian influenza is actually not limited to animals

“What we found is that it’s pretty much still there,” Puryear says. “There was no year when we did not catch the Flu in gray seals until 2012.”Like the common cold that circulates constantly among first-graders, low-trajectory avian influenza circulates more or less continuously among gray seals, which makes them more vulnerable to peril high-trajectory variants. This understanding, continues Puryear, did not make it “at all surprising when H5N1 passed [from birds] to seals last year”.

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