What Is Avian Flu?

The term “avian flu” generally refers to an infection by one of four type A influenza viruses: H5N1, H7N9, H5N6, and H5N8. The “H” and the “N” in these official names are protein markers that explain to scientists how the viruses reproduce and infect other cells. Of these four viruses, H5N1 and H5N6 most commonly cause infection in humans.

Wild birds are often infected by these viruses. Though the viruses reside in the wild birds’ intestines, they rarely cause illness. However, infected wild birds can pass the viruses to domesticated birds such as chickens, turkeys, and ducks. These birds are much more vulnerable to the viruses and often get sick and die when infected. Domesticated birds can easily infect each other, leading to outbreaks. In December 2021, the first North American cases of a new H5N1 strain occurred in Newfoundland and Labrador, Canada. Since then, the strain has spread to other Canadian provinces and U.S. states. This H5N1 strain is highly contagious and has affected commercial poultry, non-commercial flock poultry, and wild birds, leading to the deaths of 37.55 million chickens and turkeys as of May 2022.

Mammals are at risk, too. In October 2014, the H10N7 strain of avian flu was found to have killed over six hundred seals off the coasts of German North Sea islands. In December 2016, an outbreak of the H7N2 strain infected cats—and one human attendant—in a New York City animal shelter. And rare cases of human infection with yet another type A virus, H9N2, have been reported in several countries, usually in children. The H5N1 strain of the avian flu has been known to spread to mammals, including foxes, cats, dogs, and ferrets. In March 2024, the highly pathogenic avian influenza (HPAI) strain of the H5N1 avian flu was detected for the first time in dairy cows on farms in Kansas and Texas. HPAI A(H5N1) was also detected for the first time in goat kids (juvenile goats) on a farm where a poultry flock had tested positive for the same virus. The following month, health officials announced that a dairy farm worker in Texas had developed conjunctivitis, a mild eye infection, from contact with cows infected with H5N1. Risk to humans remains low, however, and the H5N1 virus is killed during pasteurization of dairy products, meaning drinking milk is of “no concern,” said officials at the U.S. Department of Agriculture (USDA).

Bird Flu in Humans

It is not easy for humans to become infected with the virus. Most of those who have become ill came into contact with bird feces (solid waste), urine, saliva, or other secretions. Symptoms are similar to ordinary flu symptoms—cough, fever, aches, breathing difficulty, sore throat, pneumonia—but they are faster developing and more severe. Studies have shown that avian flu can be transported from one place to another via clothing, shoes, or even tractor wheels. Anyone who kills, de-feathers, butchers, or prepares an infected bird is at high risk. Open-air markets where people sell chickens or other domesticated birds are considered hotbeds of infection.

Despite all this, it is extremely rare for the virus to be passed from person to person. Furthermore, there has never been a documented case of person-to-person-to-person transmission, meaning the virus does not seem to continue on to a third person after a second person is infected.

The number of human cases of avian flu has increased over the last two decades, since the first documented case in 1997. Given the number of birds that have the virus, however, the number of humans infected remains quite low. Because of these factors, the possibility of widespread infection is greatly reduced. In April 2022, the first human case of the H5N1 avian flu strain in the 2021–2022 outbreak was detected in a man in Colorado. The first case internationally for this outbreak occurred in December 2021 in the United Kingdom. In April 2024, during a global outbreak of avian flu, the U.S. Centers for Disease Control and Prevention (CDC) issued a health alert to inform the public of a confirmed human infection of the bird flu. A worker on a commercial dairy farm in Texas developed conjunctivitis, commonly known as pink eye, and later tested positive for HPAI A(H5N1). Before this incident, there had been no previous reports on the spreading of HPAI from cows to humans.

Threat of a Pandemic

There are fears that avian flu could spread across the globe, infecting and killing thousands or even millions of humans in a deadly pandemic. A pandemic is a global outbreak of a disease, often spreading easily from person to person like the COVID-19 virus did in early 2020. However, the truth is considerably less alarming. At this point, you have little chance of contracting avian flu, especially if you do not handle birds or eat undercooked poultry or eggs.

Still, scientists fear the virus may mutate in such a way that person-to-person transmission will become easier, leading to the possibility of an epidemic or pandemic. Preparations are being made for this worst-case scenario. Epidemiologists (who study the cause of diseases and the way they spread) and other researchers are working overtime to test effective medications to treat the disease. To that end, the U.S. government has stockpiled vaccines for avian influenza viruses for use in an epidemic or pandemic.

On the flip side, a controversial program to modify the H5N1 virus in ways that could make it more transmissible in—and more deadly to—mammals was restarted at two laboratories in the U.S. in 2019. The program, designed to research avian flu in order to be better prepared for a potential pandemic, was shut down for several years in 2014 out of fears that it could pose a threat to human health.

This is by no means the first deadly global flu scare in history and it won’t be the last. Keep in mind that very few of these scares have emerged as the deadly scourge they were initially feared to be.