Is Bird Flu A Danger To Humans? Here’s What Scientists Know Right Now

Eggs, the breakfast of champions (chugged raw if you’re Rocky Balboa), are now an unlikely luxury item. Outbreaks of avian influenza affecting poultry have at least partially contributed to the nationwide shortage of eggs.

But it’s not only eggs. Spikes in cases of avian flu, particularly the H5N1 strain, over this past year among mammals have been raising fears of the virus spreading to other species, including humans. Should you be worried? Here’s what you need to know.

What is bird flu?

Avian influenza is part of a family of influenza viruses, which come in four types (A, B, C, and D), causing respiratory infections in both animals and humans. Types A (to which avian influenza belongs) and B viruses are responsible for seasonal flu epidemics we commonly associate with the flu season. These two viral types have surface proteins — hemagglutinin and neuraminidase — that constantly switch up, resulting in new strains emerging and causing periodic epidemics (and the reason why we reformulate our flu vaccines every year).

Like the flu viruses that infect us, avian influenza crops annually and infects quite a number of wild birds as well as poultry, Gary Butcher, a veterinarian and virologist at the University of Florida’s College of Veterinary Medicine, tells Inverse.

“It’s actually a natural part of the cycle of life for the migratory and shore birds,” he says. “Every year, when birds start migrating out of Canada, a very large number of them are infected and [are actively spreading the virus]. This is normal, and it’s been going on for tens to hundreds of thousands of years.”

Butcher says most of these animals eventually get over their infection and develop immunity to the virus. But a problem arises when the infectious invader hops over to other birds like chickens, turkeys, and other commercial livestock.

The low pathogenic form of the virus, called low pathogenic avian influenza (or LPAI), causes mild illness or none at all, the only symptoms being some respiratory issues, ruffled feathers, or a drop in egg production. On the whole, most avian influenza viruses are of this variety, but in poultry and potentially other animals, these infectious microbes can mutate into the highly pathogenic form of the virus. Called highly pathogenic avian influenza (HPAI), this form carries a very high mortality rate among chickens and turkeys, affects multiple internal organs, and causes death in 90 to 100 percent of chickens within 48 hours, according to the CDC.

The current strain running amok in the US and Europe is H5N1 (the H and N referring to the surface proteins) and is one of several avian influenza viruses classified as highly pathogenic. This strain was first detected in domestic waterfowl in 1996 in southern China and spread to migratory birds around 2005.

Can it infect other animals?

Yes, it can. So far, there’s been reports of H5N1 cases or outbreaks in a variety of mammals like sea lions, grizzly bears in Montana, minks on a farm in northwestern Spain, and several other mammals. In total, 17 non-bird species have been infected in 20 states, reported CNN.

Because proteins the virus needs to infect the upper airways, called receptors, are less common in mammals, H5N1 doesn’t tend to infect them, says Butcher.

So far, most infectious cases in mammals have been due to them feeding on infected prey, Jonathan Runstadler, professor and chair of the Department of Infectious Disease & Global Health at Tufts University Cummings School of Veterinary Medicine, and Wendy Puryear, a scientist at the same institution, jointly tell Inverse in an email.

This mode of transmission and any other sort of interaction makes it all the more critical to keep domestic animals and pets like dogs and cats away from wildlife, so they don’t get infected.

The outbreak of H5N1 at the mink farm in Spain does stir up fears that transmission may be happening between mammals (Butcher says minks are one the mammals more susceptible to the virus overall). Sequenced virus samples taken from four minks showed unique mutations compared to the avian influenza strain, Science reported last month. The significance of these mutations remains unknown, and it’s unclear whether these were present when the virus was transmitted from an infected bird or if they occurred while in the mink. Importantly, none of the workers at the mink farm became infected.

Does it infect humans? Should we be worried?

At a press conference last week, Tedros Adhanom Ghebreyesus, the WHO’s director-general, told reporters that “the recent spillover to mammals needs to be monitored closely” but that “for the moment, WHO assesses the risk to humans as low.”

Again, the proteins that make it possible for the virus to infect mammals are largely lacking in humans.

“Some people have [those specific] receptors but in small numbers,” says Butcher. “You [would] need an incredible amount of virus to get down deep into the respiratory system where humans have these receptors.”

Runstadler and Puryear agree the risk to humans is low, but the ongoing spillovers to other mammals — acquiring new mutations that make mammal-to-mammal transmission possible, make it more efficient at avoiding immune system detection — raises the concern that the risk may not stay low forever.

Additionally, they say this situation makes it all the more important for public health authorities to remain vigilant and for disease surveillance systems to receive the funding they need to effectively collect information on any changes in the virus and what those changes will mean for us, other animals, and the environment.

According to the CDC, there have been less than 10 known cases of avian flu from H5N1 among humans globally since December 2021, however, none were due to human-to-human transmission. The most recent case in the U.S. occurred in late April 2022 with a person in Colorado who got sick after killing infected birds. The person reported being tired for a few days but, after isolation and antiviral treatment, got better, reported the CDC.

The agency recommends the best way to protect yourself is to avoid direct contact with wild birds. If this has got you wary of handling poultry, don’t be — food and safety regulations, which include regular monitoring of bird flu, are very strict in the U.S., so your chicken tenders and eggs are safe to consume, as long as you’re handling them hygienically.

While the seasonal flu vaccine won’t protect you against avian influenza, it can reduce the risk of getting sick with both human and bird viruses, according to the CDC. So if you haven’t been vaccinated, here’s your sign to go do it now.