Could Bird Flu Be the Next Pandemic?

Three decades of working with elephant seals couldn’t prepare Marcela Uhart for the scene that greeted her on the beaches of Argentina’s Valdés Peninsula last October.

It was “just carcass upon carcass upon  carcass,” recalls Uhart, a veterinarian at the University of California, Davis. It was, she says, “an image from hell.”

Uhart and a colleague documented the devastation, and what they found was shocking: H5N1, one of the many viruses that cause bird flu, had killed an estimated 17,400 seal pups, more than 95 percent of the colony’s young animals.

The catastrophe was another brutal development in a bird flu epidemic that has killed millions of birds and other animals around the world since 2020. In the United States alone, authorities have destroyed more than 95 million birds in a futile attempt to slow the virus. The outbreak has spread to American dairy cows, affecting more than 200 herds in 14 states since March.

Marcela Uhart has worked with elephant seals for thirty years. But that didn’t prepare her for what she saw on the beaches of the Valdés Peninsula in Argentina last October.

It was “just carcass upon carcass upon carcass,” recalls Uhart, a veterinarian at the University of California, Davis. It was, she says, “an image from hell.”

Uhart and a colleague recorded the scene. What they found was shocking. An estimated 17,400 seal pups were killed by H5N1. It is one of the many viruses that cause bird flu. More than 95 percent of the colony’s young animals had died.

This was another horrible development in the ongoing bird flu epidemic.  Millions of birds and other animals around the world have died since 2020. In the United States alone, authorities have destroyed more than 95 million birds to try to slow the virus. The outbreak has spread to American dairy cows. More than 200 herds in 14 states have been infected since March.

Bird flu, or avian influenza, is a group of flu viruses that primarily infect birds. The particular virus in these recent cases, H5N1, was first identified in 1996 in geese in China. The first report of human infection happened in Hong Kong in 1997, where it infected 18 people, killing 6.

There’s been no stopping H5N1, which has continued to evolve and is highly pathogenic—meaning it has the ability to cause severe disease and death. Avian flu viruses tend to be picky about their hosts, typically sticking to one kind of wild bird. But this one has rapidly infiltrated a wide array of birds and animals, from squirrels and bottlenose dolphins to polar bears and skunks.

The blow to sea mammals—and to the dairy and poultry industries—is worrying enough. But a bigger concern, experts say, is what these developments could indicate: The virus is adapting to mammals, edging closer to being able to spread widely from person to person.

“Every time [the virus] jumps to a mammal, there’s an opportunity for tiny changes” that may help it more easily infect people, says Meghan Davis, an associate professor at the Johns Hopkins Bloomberg School of Public Health.

Past pandemics—including, many experts say, Covid-19—have often begun with a virus “spillover” from animals to humans (see “From Animals to Us,” below).

Bird flu, or avian influenza, is a group of flu viruses that primarily infect birds. Recent cases have been caused by the virus H5N1. It was first identified in 1996 in geese in China. The first report of human infection happened in Hong Kong in 1997. Eighteen people were infected and six people died.

There’s been no stopping H5N1. It has continued to evolve and is highly pathogenic, meaning it has the ability to cause severe disease and death. Avian flu viruses tend to be picky about their hosts and normally infect only one kind of wild bird. H5N1 has rapidly spread to a wide variety of birds and animals, from squirrels and bottlenose dolphins to polar bears and skunks.

The loss of sea mammals—and impact on the dairy and poultry industries—is worrying enough. Experts are concerned about what this could mean for humans. The virus is adapting to mammals, which could result in it spreading widely from person to person.

“Every time [the virus] jumps to a mammal, there’s an opportunity for tiny changes” that may help it more easily infect people, says Meghan Davis, an associate professor at the Johns Hopkins Bloomberg School of Public Health.

Past pandemics—including, many experts say, Covid-19—have often started with a virus “spillover” from animals to humans (see “From Animals to Us," below).

In 2020, a new, especially deadly, form of H5N1 emerged in wild birds in Europe and spread quickly around the world. It killed scores of farmed birds, but it also spread widely among wild birds and into other animals.

The virus can spread from birds to other species in different ways. An animal could eat a dead bird that’s been infected or come into contact with its droppings or saliva. Many experts believe the current outbreak among U.S. dairy cows began with infected wild birds spreading the virus in the cows’ food or water.

The dairy cow outbreak is worrisome, Davis says, because humans “have a lot of touch points with dairy cows,” particularly dairy farm workers and consumers who drink raw milk—which isn’t pasteurized, or heated to a high temperature to kill viruses and other germs. Eating raw meat and raw eggs also increases the risk of exposure.

Since March, the World Health Organization (W.H.O.) has been notified of 23 cases worldwide, and at least 3 deaths.

In 2020, a new, especially deadly, form of H5N1 emerged in wild birds in Europe. It spread quickly around the world. It killed countless farmed birds, but it also spread widely among wild birds and into other animals.

The virus can spread from birds to other species in different ways. An animal could eat a dead bird that’s been infected. Animals can come into contact with infected birds’ droppings or saliva. Many experts believe the current outbreak among U.S. dairy cows began with infected wild birds spreading the virus in the cows’ food or water.

The dairy cow outbreak is worrisome, Davis says, because humans “have a lot of touch points with dairy cows.” Dairy farm workers and consumers who drink raw milk are at risk. Raw milk hasn’t been pasteurized, or heated to a high temperature to kill viruses and other germs. Eating raw meat and raw eggs also increases the risk of exposure.

Since March, the World Health Organization (W.H.O.) has been notified of 23 cases worldwide and at least 3 deaths.

As of October, eight U.S. dairy workers and nine poultry workers had tested positive for H5N1 this year—with largely mild symptoms, but experts believe many more have been infected.

In September, U.S. health officials identified a possible cluster of eight human bird-flu infections in Missouri, none of them from known exposures to infected animals. One patient with gastrointestinal symptoms tested positive for H5N1, and seven others in close contact developed symptoms. As of last month, researchers were testing their blood samples for signs of infection.

“We should be very concerned at this point,” says Dr. James Lawler, co-director of the University of Nebraska’s Global Center for Health Security. The possible cluster could mean “the virus is inching closer and closer to what would be a real pandemic virus . . . that is when Pandora’s box is open.”

As of October, eight U.S. dairy workers and nine poultry workers had tested positive for H5N1 this year. They had mild symptoms, but experts believe many more have been infected.

In September, U.S. health officials identified a possible cluster of eight human bird-flu infections in Missouri. None of the cases were from known exposures to infected animals. One patient with gastrointestinal symptoms tested positive for H5N1. Seven others in close contact also developed symptoms. As of last month, researchers were testing their blood samples for signs of infection.

“We should be very concerned at this point,” says Dr. James Lawler, co-director of the University of Nebraska’s Global Center for Health Security. The possible cluster could mean “the virus is inching closer and closer to what would be a real pandemic virus that is when Pandora’s box is open.”

The Centers for Disease Control and Prevention (C.D.C.) says the risk for the general public remains low. The C.D.C. and other health agencies have monitored H5N1 for years. The U.S. has stockpiled vaccines and drugs to be used in a possible bird flu outbreak.

Scientists are watching closely for mutations that could make H5N1 more likely to infect people or resistant to available vaccines and drugs. Global health groups including the W.H.O. and the C.D.C. routinely share information and genetic sequences to monitor which flu strains are spreading and where.

In the U.S., many public health experts believe the government should be more aggressive about testing and vaccinating cows and farmworkers, and worry about the government’s ability to rapidly increase the production of tests.

“Nobody should be hitting the panic button yet,” Lawler says, “but we should really be devoting a lot of resources into figuring out what’s going on.”

The Centers for Disease Control and Prevention (C.D.C.) says the risk for the general public remains low. The C.D.C. and other health agencies have monitored H5N1 for years. The U.S. has stored vaccines and drugs to be used in a possible bird flu outbreak.

Scientists are watching closely for mutations in the virus. They are looking for changes that could make H5N1 more likely to infect people or resistant to available vaccines and drugs. Global health groups including the W.H.O. and the C.D.C. share information and genetic sequences to monitor which flu strains are spreading and where.

In the U.S., many public health experts believe the government should be more aggressive about testing and vaccinating cows and farmworkers. They also are concerned about the government’s ability to rapidly increase the production of tests.

“Nobody should be hitting the panic button yet,” Lawler says, “but we should really be devoting a lot of resources into figuring out what’s going on.”

Apoorva Mandavilli and Emily Anthes are science reporters for The New York Times. With additional reporting by Lauren Vespoli.

Apoorva Mandavilli and Emily Anthes are science reporters for The New York Times. With additional reporting by Lauren Vespoli.