Final summer season, the extremely contagious pressure of avian influenza that had been spreading via North American birds made its manner into marine mammals, inflicting a spike in seal strandings alongside the coast of Maine. In June and July, greater than 150 useless or ailing seals washed ashore.

Now, a examine supplies new perception into the outbreak. Of the 41 stranded seals examined for the virus, almost half had been contaminated with it, scientists reported on Wednesday within the journal Rising Infectious Ailments. It’s probably that wild birds launched the virus to seals at the very least twice, the researchers concluded. In a number of seals, the virus had mutations which are related to adaptation to mammals.

The danger to people stays low, and the seal outbreak waned shortly, the scientists mentioned.

“It was a dead-end occasion, so far as we will inform,” mentioned Kaitlin Sawatzki, a postdoctoral researcher on the Cummings College of Veterinary Medication at Tufts College and an creator of the brand new paper. “The virus that entered into these seals has not endured.”

However the report comes amid rising considerations that the virus, which has already induced the biggest chook flu outbreak within the nation’s historical past, may adapt to unfold extra effectively amongst mammals, doubtlessly sparking a brand new pandemic.

It stays unclear whether or not the seals had been spreading the virus to at least one one other or primarily choosing it up from birds. However the variety of affected seals means that both the virus spreads simply among the many marine mammals or that the barrier for bird-to-seal transmission is low.

“We really don’t know if it’s transmitting from chook to seal, chook to seal, chook to seal 100 instances over or if it’s going into a few seals after which spreading,” mentioned Wendy Puryear, a virologist on the Tufts veterinary college and an creator of the brand new paper. “Each are potential,” she added. “Neither are nice.”

Both situation requires nearer monitoring of seals, mentioned David Stallknecht, an skilled on wildlife illnesses and influenza on the College of Georgia, who was not concerned within the analysis.

“We have to simply preserve our eyes on them,” he mentioned. “The best technique to inform if this persists in seals is to maintain testing them.”

The present model of H5N1 has turn out to be unusually widespread in wild birds and has spilled over repeatedly into mammals, together with bobcats, raccoons and foxes. Scientists consider that almost all wild mammals are contracting the virus immediately from birds.

However a chook flu outbreak on a Spanish mink farm final fall steered that the virus may unfold effectively amongst some mammalian species. And a mass die-off of sea lions in Peru has raised considerations that marine mammals is perhaps spreading the virus to at least one one other, too.

Seals are identified to be prone to avian influenza, and different variations of the virus have beforehand induced outbreaks within the animals.

The brand new examine is a collaboration between researchers at a number of tutorial establishments and wildlife organizations, together with Marine Mammals of Maine and New England Wildlife Facilities, in addition to federal scientists.

The researchers collected samples from 1,079 wild birds and 132 grey seals and harbor seals stranded alongside the North Atlantic coast from Jan. 20 to July 31, 2022. “That gave us a very highly effective means to see what is occurring within the birds and the seals in the identical time in the identical area,” Dr. Puryear mentioned.

There have been two waves of flu in wild birds, the researchers discovered. The primary, which peaked in March 2022, primarily affected raptors, whereas the second, which started in June, hit gulls and sea geese generally known as eiders.

No seals examined optimistic for avian influenza through the first wave of chook infections. However through the summer season stranding occasion, 19 of 41 seals examined optimistic.

The researchers discovered two barely completely different variations of the virus within the seals. One matched what was circulating in terns, whereas the opposite resembled what was circulating in a broader array of birds, together with gulls and eiders. The discovering means that the virus spilled over at the very least twice.

As a result of these seals don’t sometimes eat birds, the scientists suspect that the animals are choosing up the virus from the setting, maybe via contact with chook droppings.

Viral samples from the seals additionally had mutations that had been uncommon or absent in birds. Three seal samples had mutations which were proven to enhance viral replication or improve virulence in mammals.

Such mutations are usually not distinctive. In one other latest examine, a crew of Canadian scientists discovered the identical mutations in some viral samples taken from bird-flu-infected foxes. “When there’s a bird-to-mammalian spillover occasion, they appear to be acquired to fairly shortly,” Dr. Sawatzki mentioned.

The presence of those mutations isn’t, in and of itself, a purpose to “sound the alarm,” Dr. Stallknecht mentioned. However continued surveillance is important not solely to safeguard human well being but additionally to guard wild animals from a virus that has already proved devastating.

“These rising illnesses should be checked out on an even bigger scale than simply ‘pandemic potential,’” he mentioned, “as a result of they have an effect on a variety of different species on the globe.”