Over the past year, bird flu has spread far beyond America’s avian creatures. Largely concentrated among farm animals, it’s also hit zoos, domestic pets and even people.
The risk to public health remains very low. But experts are watching the disease closely as it spreads and adapts among animals, in case any changes improve it’s ability to infect to humans.
What Is Bird Flu?
Also known as avian influenza, bird flu belongs to a group of influenza viruses known as H5. It’s become widespread among wild birds all over the world in recent years, with outbreaks in poultry and cows bringing it closer to people.
In birds, the disease causes symptoms including swelling to the head, watery eyes and unusual movement. It can kill the and is animalsthought to have led to 280 million deaths since 2021. An estimated 127,470,312 poultry have been affected by the disease across 50 states.
Cows have also been seriously affected by bird flu. Nearly 900 herds of cattle in 16 states have seen bird flu infections, according to the U.S. Department of Agriculture.
The virus is not well adapted to people, so it usually results in mild disease in humans. Case numbers are still very low, with 66 human infections reported in the U.S so far this year. The disease can’t pass between humans, and most cases have been tied to animal exposure.
Bird flu has been found in samples of raw milk, leading to recalls of the product over public health concerns. Officials say pasteurized milk is still safe to drink as the process kills the virus.
What Other Animals Have Caught Bird Flu?
Bird flu has infected numerous animals besides wild birds, poultry and cows. Earlier this week, a Washington sanctuary announced the disease had killed 20 big cats died in a Washington sanctuary — more than half of the animals in its care.
The sanctuary lost one Bengal tiger, four cougars, one African caracal, two Canada lynx, one Geoffroy cat, one Bengal cat, one Eurasian lynx, four bobcats and five African servals. Infections have previously been reported in other big and wild cat species, including Asian golden cats, Amur leopards and clouded leopards.
“Cats are particularly vulnerable to this virus, which can cause subtle initial symptoms but progress rapidly, often resulting in death within 24 hours due to pneumonia-like conditions,” the Wild Felid Advocacy Center of Washington wrote on its Facebook page.
Domestic cats can also catch the disease, with an Oregan house cat recently dying after eating raw, frozen cat food tainted with bird flu. Cases have also been reported in dogs, goats and alpacas, per the Centers for Disease Control and Prevention and the U.S. Department for Agriculture. Bird flu was also responsible for the death of a polar bear in Alaska.
Over the years, U.S. wild mammals including mountain lions, bears, dolphins, seals, coyotes, foxes, martens, American minks, fishers, otters, raccoons, skunks, opossums, squirrels, mice, cottontails and prairie voles have all caught bird flu.
The disease is prominent across the globe, even spreading to the Antarctic, where it’s killed significant numbers of penguins, elephant seals and fur seals.
What’s The Risk of Bird Flu To Humans?
Special proteins on the bird flu virus help it bind to sugars on the surface of a host animal’s cells. The sugars on different animals have different shapes, some of which are fit the virus better than others.
These bird flu proteins are well-adapted for birds and cows, whose sugars are relatively similar in shape. The human equivalent is shaped quite differently, which makes it harder for the virus to get a good hold. This results in generally milder disease and stops bird flu transmitting between people.
Experts are watching the virus closely as it spreads and mutates, to see if it develops any adaptations that could make it better at binding to human cells.
Scientists at the Centers for Disease Control and Prevention announced this week they had found “low frequency mutations” to some of the proteins involved in binding in a sample from the nation’s first severe human case.
Evidence shows the virus likely mutated within the Louisiana patient, who developed serious illness from their bird flu infection earlier this month. Although it’s still “concerning,” the CDC states it would be more worrying if this changed had happened prior to this specific infection. There’s no evidence the infection spread to anyone beyond this one patient.
Experts say the mutation also isn’t enough to allow for person-to-person transmission. “Is this an indication that we may be closer to seeing a readily transmitted virus between people? No,” said University of Minnesota infectious disease researcher Michael Osterholm. “Right now, this is a key that sits in the lock, but it doesn’t open the door.”
Mutations are an normal part of the spread of a virus, which replicates itself imperfectly, resulting in the tiny changes. Most mutations will have little impact on the way a virus transmits. Bird flu may never adapt in the way it needs to to be able to pass between humans.
But just in case it does, countries including the U.S. and the U.K. have already ordered millions of doses of an H5 bird flu vaccine.
