Bird flu epidemic: is H5N1 the next pandemic? What to know after the first US death, egg shortages and milk shortages

From reports regarding first human death from bird flu in the USsome Americans have unpleasant memories of the early days of Covid-19, when infectious disease experts talked about a new virus that was sending people to the hospital with respiratory infections. Although both viruses can cause respiratory problems, they are very different.

When Covid arrived in the United States in 2020, it spread easily between people, but bird flu has been lurking for years, mostly as a problem for animals. Scientists also know much more about the H5N1 bird flu than about the SARS-CoV-2 virus, and the US has long been preparing for the threat of a new flu epidemic.

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Still, the virus is making moves that deserve attention. Here’s what you need to know about H5N1.

What is bird flu?

Avian influenza, or bird flu, is a broad term that refers to several types of influenza that commonly infect birds. The bird flu that is making news in the United States is a virus called H5N1.

Some bird-borne influenza viruses cause only mild infections and are classified as low pathogenicity viruses. In contrast, H5N1 often kills birds that catch it, which is why it is classified as highly pathogenic avian influenza.

Complicating matters, although bird flu viruses primarily feed on birds, they can also spread to other animals, including humans. Human infections with bird flu viruses are rare and usually are what scientists call dead-end infections because they do not usually spread from person to person.

Is H5N1 a new virus?

You may have only heard of H5N1 recently, but it is not a new virus. Scientists have been tracking this for almost three decades.

It was first identified in geese in southern China in 1996. Over the years, it has caused sporadic outbreaks in wild and farmed birds around the world.

The virus reemerged in North America in late 2021 and quickly caught the attention of scientists as it appeared to expand its repertoire, spreading beyond birds and infecting an increasing variety of mammals. In the current wave of infections, it has spread to more than 48 species at least 26 countries.

This caused a mass extinction marine mammals also 24,000 sea lions that died in South America in 2023. In February 2024, Dr. Jeremy Farrar, chief scientist of the World Health Organization, called continuous spread H5N1 “animal pandemic”.

From 2022, over 130 million wild and farmed birds have been affected in America in all 50 states, 919 dairy herds tested positive in 16 states, and 66 people tested positive in 10 states, according to data from the U.S. Centers for Disease Control and Prevention and the U.S. Department of Agriculture.

Could H5N1 become a new pandemic?

Scientists agree that the virus would have to evolve – or retain key changes in its genetic sequence – to cause a pandemic.

Every time a virus infects a cell and copies itself, it makes mistakes. Typically, these mistakes are benign or even harmful to the virus, but sometimes a genetic change occurs that helps the virus infect cells better. Under the right circumstances, this version of the virus can outcompete others and still survive, infecting new hosts or new types of hosts.

Flu viruses can change in other ways, too

Each virus has eight segments, and like children in the dining room, they always want to switch. When two viruses exchange entire segments, it is called reassortment and results in rapid and sometimes dramatic changes in the virus’s capabilities.

Scientists say any type of change could spell trouble for people. Although the H5N1 virus is very good at infecting birds and has become a threat to many different species of mammals, including dairy cows, it is still quite clumsy at infecting humans.

For example, in cows, the H5N1 virus mainly infects the mammary glands. This causes a dramatic drop in milk production, but does not usually kill the cow. In humans, the main route of infection appears to be the eyes; conjunctivitis, or redness and inflammation of the eyes, appears to be a characteristic symptom of infection.

Scientists think H5N1 infects the eyes because flu viruses enter cells through sugars on their surface called sialic acids. Birds – and human eyes – primarily have alpha 2,3 sialic acid receptors in their cells. However, another type of sialic acid receptor, alpha 2,6, is more common in the human respiratory tract. Human influenza viruses, including those that cause seasonal influenza, have evolved to infect cells through alpha 2,6 receptors.

Given enough time in the human body, the bird flu virus has shown the ability to change and become better at infecting different types of cells and tissues, spreading from the eyes to the respiratory tract, for example.

Scientists have detected key changes in the virus genome in a Canadian teenager who became seriously ill with H5N1 in November. These changes likely helped infect cells in the respiratory tract. Samples of the H5N1 virus that infected a seriously ill patient in Louisiana also showed signs of adaptation to human cells. Infectious disease experts warn that as the virus continues to spread, the likelihood of it turning into a fully human pathogen increases.

How do people catch bird flu?

Humans are almost always infected through contact with infected animals. Almost all of the so-called collateral infections were mild. Nor is anyone known to have contracted the H5N1 virus in the U.S. to infect anyone else.

How do we know that the disease is not spreading from person to person?
The CDC and state public health departments monitor farmworkers who test positive and trace all the people they were with while sick, a practice called contact tracing, to see if they get sick. State public health laboratories also sequence all influenza A viruses detected during routine flu testing. So far, only two cases of bird flu infection in humans have been detected this way.

The CDC estimates that the current risk to the public is low.

How can I get tested if I suspect I have bird flu?

If you become ill within 10 days of exposure to sick or dead animals or their feces, be sure to notify your health care provider of your exposure.

Although most H5N1 virus samples have been tested by state public health laboratories, the CDC is working to expand testing, and large commercial laboratories such as Quest and Labcorp now have tests that can detect H5 viruses.

This means it is easier for doctors to test patients if they suspect avian flu infection.

Who is at risk of bird flu?

The two groups of people most at risk are dairy and poultry workers and people with backyard bird flocks, said Dr. Michael Osterholm, who directs the Center for Infectious Disease Research and Policy at the University of Minnesota.

The virus inhabits the udders of milking cows research has shown high concentration of bird flu virus in raw milk.

Milking parlors in dairies are characterized by high humidity and workers can become infected if they get a drop of raw milk in their eyes or if they put milk on their hands and then rub their eyes. Droplets of virus-infected milk can also become airborne if splashed by milking equipment.

Birds spread the virus through saliva, mucus and droppings. It can be released into the air when their bedding and feathers are compacted in barns, especially during slaughter.

“It could be in the air,” Osterholm said. “So it’s not even about the contact with the birds, it’s just the dander and all the dust that comes when you’re dealing with birds.”

What are the symptoms of bird flu?

One of the most visible symptoms in infected farm workers is red and irritated eyes. A recent study of the first 46 human cases during the current U.S. epidemic found that 93% had conjunctivitis.

In approximately one third of all cases, this was the only symptom. The second most common symptom, experienced by about half of infected farm workers, was fever. About one-third of people infected with H5N1 had respiratory symptoms, but these were most common among poultry workers who were exposed during bird depopulation efforts.

Two people in North America had severe infections. The first was a 13-year-old girl from Canada who became seriously ill with lung and kidney failure and was placed on life support for two weeks to give her organs time to regenerate. It is unclear how the person came into contact with the virus.

A second person, from Louisiana, was hospitalized with severe respiratory symptoms after contact with a backyard herd and a wild bird. That person, who was over 65 years old and had underlying health conditions, died this month, the first U.S. death from bird flu.

Both patients had the D1.1 strain of the virus, which is found in wild birds. It is different from the B3.13 virus that infects dairy farm workers. Scientists are investigating whether the D1.1 strain could cause more severe disease.

Can you get bird flu from milk or meat?

Milk and meat heated to kill germs are safe.

Even before H5N1 was considered, health officials warned against drinking raw milk and eating undercooked meat, both of which could harbor nasty germs like salmonella and E. coli. Cats have died from drinking raw milk on farms.

Research by the U.S. Food and Drug Administration shows that common pasteurization methods neutralize the virus, but refrigeration does not. USDA research shows that cooking meat to a safe temperature inactivates the virus.

AND recent research from Stanford University, which involved adding the flu virus to raw milk and then testing it on cells in the lab, found that the virus could continue to infect cells for up to five days after being stored in the refrigerator.

No human infections have been linked to the consumption of raw milk, although a toddler in California recently tested positive for flu after drinking a large amount of raw milk. The CDC was unable to confirm the infection, so this child was placed on the suspect list.