H5N1 infects millions of animals. If it passes to humans, it will be worse than COVID

Public health experts continue to sound the alarm about a highly contagious avian disease that has quickly spread across the world. The virus – known as H5N1 or colloquially, bird flu – has caused significant problems over the past year, spawning a “panzootic” or pandemic in animals. The evolving disaster is contributing to the commercial shortage of eggs and killing large numbers of wild and factory-farmed animals – and a few hundred humans.

There have been 873 human cases of H5N1 since 2003, but an estimated 53% have been fatal.

True to its name, the symptoms of bird flu resemble those of the flu, which means high fever, cough, sore throat, muscle aches, diarrhea and pneumonia. Not only does the virus spread easily, but it can trigger severe illness and has a high mortality rate in humans – far higher than COVID-19.

There have been 873 human cases of H5N1 since 2003, but an estimated 53% have been fatal, comparable to some Ebola outbreaks. COVID has an estimated mortality rate of 1%, while seasonal flu is 0.1-0.2%. These rates can change with context, so they’re not always a good measure of risk, but they tell us something about the severity of the disease.

As more cases are reported in more countries, H5N1 has alarmed public health experts. Some have urged governments to stockpile flu vaccines for all strains and begin clinical trials testing new defenses against the pathogen. Dr Sylvie Briand, director of preparedness and prevention of epidemics and pandemics at the World Health Organization (WHO) described the situation as “worrying” on February 24, in particular the increase in infections in mammals. “WHO takes the risk of this virus seriously and calls on all countries to be more vigilant,” Briand said.

In Peru, for example, health officials reported the death of 585 sea lions in mid-February. As of March 3, that number had risen to nearly 3,500, which represents about 3.3% of the country’s total sea lion population, according to BNO News. The death of 63,000 birds, including pelicans, boobies and guanayes, was also reported.

Neighboring countries have also been affected, including Argentina, which detected its first case at a factory farm on March 1, responding by immediately suspending all poultry exports.

But other countries, from Spain and Chile to Estonia and Scotland, have all disclosed their own cases. In the United States alone, 47 states have experienced outbreaks of bird flu on poultry farms in the past year, resulting in the euthanasia of nearly 60 million birds to prevent further spread.

The pathogen is not new. According to the Centers for Disease Control and Prevention, reports from northern Italy in 1878 describe “avian plague” which may have been H5N1. It was not until 1955 that the virus was officially identified as an influenza A virus. In 1996, the H5N1 subtype was first identified in farmed geese in southern China and an outbreak in humans occurred in Hong Kong the following year. Eighteen people have been infected and six have died. (The name H5N1 refers to the combination of two proteins called hemagglutinin and neuraminidase.)

Genetic analysis of an outbreak in a Spanish mink farm in October found the virus detected at least one mutation that favors mammal-to-mammal spread.

Since then, public health experts have been acutely aware that H5N1 could cause big problems if it were to spread on a large scale. Despite a handful of cases over the decades, this has not been the case. While it cannot be ruled out that bird flu could trigger a pandemic in humans, experts say we are still a few evolutionary steps away from the virus for that to happen. Nevertheless, each infection is another opportunity for a mutation that could turn the tide.

This is not mere speculation; such a thing happened with SARS-CoV-2, the virus that causes COVID-19. As SARS-CoV-2 infected more and more people, it mutated again. Some of these mutations have proven beneficial, making it better able to infect humans. This is what makes all these cases of infection in mammals all the more worrying, even more so than the hundreds of thousands of birds that have died in the past year.

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Because H5N1 is a virus specifically developed to attack birds, it is not yet as effective at infecting mammalian cells. But if you can count on one thing for viruses, it’s mutating. And some versions of H5N1 have acquired genetic advantages that make it better able to spread among mammalian organisms.

For example, genetic analysis of an outbreak in a Spanish mink farm in October found that the virus had detected at least one mutation that favors mammal-to-mammal spread. Nearly 52,000 mink at the facility had to be euthanized, reminding us that mink farming is a very unwise practice. Minks also have respiratory systems similar to humans, which doesn’t bode well for us, because a flu virus that grows in minks will likely do well in humans as well.

“It’s incredibly concerning,” Tom Peacock, a virologist at Imperial College London, told Science in January 2023. “It’s a clear mechanism for an H5 pandemic to kick in.”

“As far as we can tell, the mink farm virus has not infected any workers, nor has it spread from the farm, so this particular farm outbreak is likely over,” said Peacock at Salon in an email. “The biggest risk is probably mink farming as a practice during this H5N1 outbreak – a virus only needs to be lucky once, and we think mink farming is an ideal way for a virus to learn how to spread effectively from human to human.”

Bird flu often kills its human hosts too quickly to spread very far.

In a recent blog on the Imperial College London website, Peacock questioned whether an H5N1 pandemic was “inevitable”, concluding that many open questions remain and experts disagree on the makes it impossible or inevitable.

It really comes down to the level of human infections, which so far have remained low, and whether the virus can mutate to facilitate widespread human-to-human transmission. “One thing is certain, the more the virus circulates in animals, the more it will interface with humans, setting the stage for this unlucky zoonotic event,” Peacock wrote.

Fortunately, so far, zoonotic transmissions – that is, when a virus jumps from an animal to a human – remain rare. Although a handful of people catch H5N1 each year, cases tend to multiply before becoming a major epidemic, let alone a pandemic. This is partly because bird flu often kills its human hosts too quickly for it to spread very far and because so far there are very few examples of human-to-human transmission.

Meanwhile, cases of bird flu are making headlines, such as that of an 11-year-old girl from Prey Veng province in southern Cambodia who died on February 22. Her father was also infected, but had no symptoms and 11 other people tested were negative for H5N1.

But genetic sequencing of the virus in those two cases revealed it was an older strain of H5N1, called, while the most concerning variant is named It might seem like a random jumble of numbers and letters to most people, but as we learned with SARS-CoV-2, the virus that causes COVID, even small mutations can make big differences in how these pathogens attack.

In the Cambodian case, it’s a bit of a relief that the strain is older than the one sickening birds around the world, as it doesn’t seem to have the necessary mutations to spread easily among humans. However, the WHO has reported a handful of infections with the strain, with one case in China, two in Spain, one in the UK, one in the US and one in Vietnam. All of these cases have died out and human-to-human transmission remains rare.

“We have a pretty good understanding of the minimum it would take for these viruses to become pandemic and it’s multiple mutations at once, many of which are very rare in the field,” Peacock said, but noted that many many human infections are likely missed, especially those that are mild, asymptomatic, or from areas of the world where testing is not readily available. “Furthermore, reassortment – co-infection between an avian influenza virus and a human – has the ability to allow an avian influenza virus to pick up many of these mutations at once. In fact, several previous pandemics have probably started due to reassortment between the avian influenza virus and human influenza viruses.”

Peacock advised against touching or handling sick or dead birds, especially poultry, waterfowl and seabirds. He also said to keep pets away from birds, as cats and dogs are susceptible to bird flu. Report groups of dead birds or wild scavengers that are obviously sick or behaving strangely (such as convulsing, paralyzing or shaking) to the local health authority.

Despite the relatively low level of risk at present, many countries are preparing flu vaccines and antiviral drugs, such as baloxavir and tamiflu, which are believed to be effective against H5N1. The United States currently stocks vaccines for many influenza viruses, including H5N1. According to the New York Times, the CDC is sending flu virus samples to pharmaceutical companies to help them develop vaccines while exploring whether commercial test makers are interested in developing H5N1 tests similar to those used to detect the virus. COVID.

But a pandemic need not be extremely deadly to cause widespread destruction. Even a sharp increase in hospitalizations and sick workers could wreak havoc. Although this panzootic is heating up, it still has a long way to go before it turns into a human pandemic.

“It’s a really dangerous time to be a bird,” Andrew Pavia, chief of the division of pediatric infectious diseases at the University of Utah, told Scientific American. “But to date the risk to humans remains very low. Our concern is what will happen as it circulates more and more.”

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