“There’s a lot we don’t know”: Why public health experts are worried about bird flu

The Centers for Disease Control and Prevention (CDC) issued a health alert last week regarding a confirmed case of H5N1 in a human.

In late March, a worker at a commercial dairy farm in Texas developed a case of conjunctivitis and later tested positive for highly pathogenic avian influenza type A H5N1, also known as “bird flu” or bird flu.

Although the farmworker had no symptoms other than eye inflammation and was not hospitalized, he was isolated and received antiviral treatment, according to the CDC. The public health agency suspects the patient was infected by a sick dairy cow.

Although bird flu is not new, this is the first time authorities have confirmed that the virus has jumped from a cow to a human, and the transmission line suggests it is easily transmitted between cows. The last time a human tested positive for H5N1 was in April 2022 in Colorado, when an individual was infected by poultry.

The fact that it jumped from livestock to humans is troubling, experts say, and a cause for concern. But not necessarily, because H5N1 will turn into a pandemic this year.

“There’s a lot we don’t know,” virologist Angela Rasmussen told Salon. “We don’t actually know what kind of risk the cows themselves pose.”

It seems “clear” that cows can pose a risk to each other, Rasmussen said, but what kind of risk that poses to cow health is not completely understood. And neither is the kind of risk it poses to human health.

In birds, HPAI is highly contagious and deadly. The big problem is that the more it passes from animal to animal, or from animal to human, the more likely it is to mutate to better infect humans. Of course, RNA viruses like influenza and SARS-CoV-2, which cause COVID-19, are always mutating. Each replication in a host’s cells presents a chance for a mutation to emerge. Although viruses are not technically alive, it is their nature to mutate and evolve as they infect host cells and replicate. This is how they reproduce. Thus, understanding how H5N1 mutates is critical to assessing the potential risk to animal and human health and how close the United States might be to an avian flu pandemic.

Fortunately, bird flu does not appear to pass from person to person, public health officials say. According to the CDC, the current risk these viruses pose to the public remains low. In fact, the CDC sequenced the genome and compared it to other sequences from cattle, wild birds, and poultry. The study found no major changes, except for one: The human sample had a mutation called PB2 E67K, known to link the virus’s adaptation to mammalian hosts. This has already been observed in people infected with H5N1.

“It is the enzyme that essentially copies the virus as it replicates and has been associated with mammalian adaptation, but it is only one mutation in a set of mutations associated with mammalian adaptation.” , Rasmussen said. “So this suggests that when the virus was transmitted from the cow to the person, she contracted this mutation.”

However, Rasmussen stressed that this “does not mean that the virus is better suited to transmission between mammals”, which is good news. “It just means – as you would expect – that it is a second mammalian host species,” she said. “So it’s about taking the adaptations that we’ve already seen that are associated with mammalian adaptation.”

Dr. Rajendram Rajnarayanan of the New York Institute of Technology campus in Jonesboro, Ark., also believes the risk of human-to-human transmission is low. However, he is concerned about the virus spreading to other mammals on a farm, such as pigs.

Pigs, Rajnarayanan said, can be infected with multiple viruses at once. This could make it easier for the virus to mutate into a new virus that could more easily pass from one mammal to another, such as, for example, from one human to another.

“It needs a mixing pool, like pigs,” he said, “to effectively infect the human respiratory tract and then invade different parts of the body and cause more serious damage.”

In the United States, there have been no known recent cases of human-to-human transmission. Although they occurred in other countries, these cases did not spread beyond close contact and were contained before becoming an epidemic. Certainly, the consensus among scientists is that the latest case of bird flu does not currently pose a panic threat to human health. This could happen in the future, especially if it ends up infecting a host like pigs.

“The likelihood of bird flu becoming the next pandemic next year is probably quite low,” Dr. Linda Yancey, an infectious disease specialist at Memorial Hermann Health System in Houston, told Salon. “The likelihood of bird flu becoming a pandemic within the next century is probably quite good.”

However, this does not mean that individuals should not change their behavior. In light of the news of the infection, people should refrain from drinking unpasteurized milk.

“It’s very important to make sure you’re not drinking unpasteurized milk,” Yancey said. “Our milk supply is extremely safe. We pasteurize it, but sometimes people, for whatever reason, drink unpasteurized milk.”

Indeed, one of the main concerns among experts is the potential impact on the milk supply chain. Rasmussen also worries about the potential economic impact.

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“We don’t even really appreciate the magnitude of the number of cows that could be affected,” Rasmussen said. “It appears to be associated with dairy cattle rather than beef cattle, but there are interactions between these two industries.”

This is normally the time when Rasmussen tells the public to get vaccinated. Although avian flu vaccines are under development, none have yet been approved for use in humans. Notably, according to the CDC health alert, in the strain identified in the Texas case, there is no indication that avian flu has developed resistance to antiviral drugs, meaning that even without vaccines, some drugs could potentially work against She.

Nonetheless, the CDC is asking health care professionals across the country to watch for signs of bird flu and consider it a possibility when patients have been exposed to sick or dead birds, livestock, or other animals a week before the appearance of symptoms. Humans are also advised to stay away from sick or dead animals.

“It’s actually been a global animal population crisis over the last three years,” Rasmussen said. “If people want to translate their concerns into action, I strongly suggest advocating for additional measures and increased investments in pandemic preparedness.”