Avian flu is not yet a direct threat to humans, but experts warn

Avian flu has infected record numbers of birds and some mammals in the United States, and scientists are watching closely.

World Health Organization Director-General Tedros Adhanom Ghebreyesus said last week that the risk to humans remains low, but added: “We cannot presume that this will continue to be the case.”

As with the coronavirus that causes Covid-19, which is believed to have started in animals before spreading to humans, some animal viruses can mutate, skip species to make humans sick, and spread rapidly around the world.

But highly pathogenic avian flu is not Covid-19. Scientists are assuring the public that, with a few rare exceptions, the virus has not reached humans on a large enough scale to trigger an outbreak.

It has gone far beyond birds, and its recent spread among members of a separate species has some experts worried about the way the virus is changing.

What is avian flu?

Avian flu is a type A influenza virus that originated in birds. The version that is causing problems predominantly in the Americas and Europe is called H5N1. There are several subtypes, and the commonly circulating H5N1 avian flu viruses now are genetically different from earlier versions of the virus, according to the US Centers for Disease Control and Prevention.

As of late 2022, scientists have detected this virus in more than 100 species of wild birds such as ducks, gulls, geese, hawks and owls in the US.

Globally, this strain of the virus has been around for much longer, said Richard Webby, an infectious disease researcher at St. Jude Children’s Research Hospital in Memphis, Tennessee, and director of the WHO Collaborating Center for Studies on the Ecology of Influenza in Animals and Birds.

“We saw a sort of great-great-grandfather virus in the late 1990s in Southeast Asia, and we’ve been following its evolution and change ever since,” Webby said.

In the 2000s, it spread to parts of Europe and Africa and then was carried to the rest of the world via infected migratory birds. It arrived in the Americas more recently, Webby said.

The first infection with this version of the virus was reported in wild birds in the US in January 2022, according to the CDC (US Center for Control and Prevention) – the body that corresponds to Anvisa in Brazil. The following month, the US Department of Agriculture announced an outbreak among turkeys at a commercial facility.

Studies have shown that avian flu can be spread to songbirds, but those that normally congregate at bird feeders – like cardinals, house sparrows or blue jays – and those you might see on the street like pigeons or crows typically don’t carry avian flu viruses. to be a threat to humans, according to the CDC.

Ducks and geese can carry the virus without looking sick. Domestic birds are not always so lucky.

Highly pathogenic avian flu carries “very high death rates” among chickens and turkeys. The disease can affect multiple internal organs, causing death in 90% to 100% of chickens within 48 hours of infection, according to the CDC.

Because it can spread so quickly, farmers often have to cull uninfected birds along with infected ones to prevent a wider outbreak. It is considered one of the greatest known threats to domestic birds.

Until Wednesday (15), 6,111 cases were detected in wild birds in all 50 states, says the USDA (United States Department of Agriculture, its acronym in English). The virus has affected more than 58.3 million birds in 47 states, according to the CDC.

The sheer volume of cases means the virus is more likely to spread to other species, experts say.

More animals getting sick

Avian flu is spread through things like feces and saliva. It can also spread through contact with a contaminated surface.

The virus has infected many mammals in the US, mostly in the West and Midwest, as part of the latest outbreak.

In Alaska, cases have been reported among bears and foxes, according to the USDA. The virus has also been found in a bobcat in California, a skunk in Colorado, a raccoon in Washington, skunks in Illinois and Iowa, a mountain lion and a grizzly bear in Nebraska, seals in Maine and even a dolphin in Florida.

In total, 17 different animal species were infected in 20 states.

Scientists say that all of these sick mammals likely caught the virus when they ate or interacted with infected birds.

But in a worrying development last fall, the virus appeared to be spreading among mammals – perhaps for the first time – on a mink farm in Spain, according to a study published in the journal Eurosurveillance.

The mink got a bloody nose, developed tremors, lost its appetite and appeared depressed, the scientists said, and had to be killed to keep the threat at bay.

The virus did not spread to the humans working on the mink farm, but what worried scientists was the multiple mutations found in the virus that made it distinct from the sequences found in birds. A mutation made it better replicate in mammals, although it’s unclear whether the mutation was in the virus before it reached the farm.

“But it’s when it starts to spread from one mammal to the next mammal to the next mammal, it’s in those environments where we think it’s more likely to pick up those changes that allow us to switch hosts, and that’s why we’re concerned,” said Webby.

A handful of human cases

There have been fewer than 10 known cases of avian flu in humans since December 2021, and none have come from human-to-human transmission, the CDC says.

The most recent case in the US was in a person in Colorado who became ill after culling infected poultry in April. The person reported being tired for a few days. They were isolated and treated with an antiviral, according to the CDC.

The agency said at the time that the threat to public health remained low, but urged people who had any exposure to birds to take precautions.

“The people who typically get sick are those who have very intense interactions with wildlife, dead or alive,” said Dr. W. Ian Lipkin, director of the Center for Infection and Immunity and professor of epidemiology at Columbia University Mailman School of Public Health. “I wouldn’t say there’s another pandemic upon us, because it’s not. They weren’t there.

“What we need to do now is watch closely how this spreads. We need to contain it on farms and in wildlife as best we can,” she added.

how to stay safe

While the threat to people is low, the CDC suggests avoiding direct contact with wild birds.

Webby says that if you must handle a dead bird, such as removing it from a feeder, wear gloves and a mask. Always wash your hands after touching birds or feeders.

It’s safe to eat poultry and eggs that are handled and cooked properly, the CDC said. Avian flu is not a foodborne illness, and the poultry industry is closely monitored and has strict health standards that include monitoring and control of avian flu.

Always cook poultry and eggs at 75 degrees Celsius, a temperature that kills bacteria and viruses, including bird flu.

In the highly unlikely event that someone becomes sick, the CDC recommends immediate treatment. Most bird flu infections can be treated with currently available antiviral drugs, the agency says.

The US government also has a stockpile of vaccines, including those against the avian flu virus, which could be used if the flu spreads easily from person to person, the CDC says.

“The chances are not zero that you’ll get it, and anything you can do to further reduce that risk is a good thing,” Webby said. “But you probably really have to work hard to get infected with this virus.”