Does Bird Flu Pose a Major Risk to Humans?
It’s a bird pandemic, not a human one. At least, not yet.
Since 1997, when the trouble-making strain of the bird flu virus, H5N1, was first detected in China, many millions of birds have died from the disease, according to the U.S. Department of Agriculture.
A few hundred human cases have been reported since then, half of whom have died. That, scientists believe, serves as evidence that H5N1 can be lethal in our species. However, the virus hasn’t mutated to a point where people can infect other people. Humans can only get bird flu from infected birds—and now, possibly, cows.
“Currently, the risk to most people is low,” says Dr. Heidi Torres, Assistant Professor of Clinical Medicine in the Division of Infectious Diseases and Assistant Hospital Epidemiologist at Weill Cornell Medicine. “But we can’t predict how the virus, like many other influenza strains, may mutate in the future, so the risks could change.”
How might the H5N1 strain mutate to a point where it becomes easily transmissible between humans?
“It’s possible that will happen, as other influenza strains have done in the past,” Dr. Torres says. “Typically, animal viruses, also known as zoonotic diseases, aren’t compatible with human cells, which is why they don’t often jump from animals to humans. However, if the virus’s surface proteins mutate, they could enable it to bind to human cells and cause infection.”
Other zoonotic diseases that have made the jump from animals to humans include SARS (severe acute respiratory syndrome), MERS (Middle Eastern respiratory syndrome) and, of course, SARS-CoV-2, the coronavirus that causes COVID-19.
“Additionally,” she adds, “H5N1 could mix with another influenza strain that is more compatible with humans. This type of genetic reassortment was responsible for the H1N1 pandemic in 2009.”
A new wrinkle
Since March of this year, bird flu has been reported in a very different animal: dairy cattle. So far, 13 states have reported outbreaks, affecting 192 dairy herds and counting.
The virus’s jump to cows has shocked scientists, who were unaware that cows were susceptible to it. It has also been found in other mammals, including foxes, bears, otters, raccoons, cats, dogs, goats and mink. More than 5,000 sea lions died of it in late 2023.
There have been 4 cases of bird flu in American agricultural workers so far. Particularly disturbing, however, was a 59-year-old man in Mexico who contracted another type of bird flu, caused by the H5N2 strain. He died earlier this summer with the infection, not of it, according to the World Health Organization (WHO). Still, no one knows yet how he got infected.
How can the bird flu virus in dairy cattle be controlled?
Tracking viral infections on poultry and cattle farms has become an urgent priority. Strengthening our health-care infrastructure is also urgent. That’s the best way to guard against the worst eventuality: a bird flu epidemic among humans.
Where outbreaks in livestock or poultry are concerned, the U.S. Department of Agriculture (USDA) collaborates with national and local agencies to prevent and control the spread of disease. Since H5N1 was first detected in dairy cows in March, the USDA and its partnering agencies have recommended several measures:
- keeping livestock away from birds;
- monitoring for signs of illness;
- frequent disinfection; and
- milk testing.
“They’re also tracking animal movements and monitoring disease prevalence in herds,” Dr. Torres says. “Sick cows should be isolated and monitored. The continued spread of the disease among dairy cows is likely due to the movement of cows between herds, the use of potentially contaminated farming equipment and the presence of infected local poultry. Given that frequent movement is a normal part of farming operations, it’s challenging to completely prevent exposure. By the time an infected animal is identified, significant exposure to other animals may have already occurred.”
The public health response we need
Having been through the COVID pandemic and come out the other side, the country is better prepared to deal with bird flu before it reaches epidemic levels.
A public health response to any potential respiratory virus epidemic, Dr. Torres says, should include the following components:
- ensuring that frontline providers are aware of circulating cases to facilitate faster diagnosis;
- ramping up testing and treatment capacity;
- ensuring that clinics and hospitals have adequate PPE, supplies and capabilities to manage an influx of patients;
- producing and distributing a vaccine; and
- providing educational resources to help the public manage exposure and illness.
Why is bird flu difficult to diagnose in cows and humans?
The symptoms of bird flu in both cows and humans—a runny nose, fever, body aches, fatigue and irritated eyes (conjunctivitis)—may also be caused by allergies, a cold or COVID-19. That’s why it’s so devilishly difficult to diagnose in cows and in people.
“Healthcare providers should be particularly concerned if a patient has had close contact with wild birds, poultry or cows,” says Dr. Torres. “In such cases, swabs can be taken to test for influenza, and if positive, further tests can identify the H5N1 strain. In cows, symptoms differ from those in humans and may include decreased appetite, reduced or abnormal milk production and changes in bowel movements. A diagnosis of H5N1 in cows can be confirmed through nasal swabs, tissue samples and milk testing.”
How might a potential bird flu epidemic among humans be stopped in its tracks?
If there are signs that the virus is spreading between humans, the key steps will be similar to those taken during the COVID-19 pandemic as well as past influenza epidemics:
- Sick individuals will need to self-isolate, practice good hand-washing hygiene and wear a mask.
- Frontline staff should be able to recognize signs of illness and administer testing and treatment.
- Vaccine development and deployment will also be crucial.
Although H5N1 vaccination is not currently recommended, work is already underway to create a vaccine targeting the circulating strain. Additionally, older H5N1 vaccines targeting previous strains are available in the U.S. national stockpile and may be of use, if needed.
Will prior knowledge about the flu virus help in the event of a bird flu epidemic among humans, especially with vaccine development?
“We already know a great deal about the influenza virus and its currently circulating variants, and we can build on that knowledge even before a bird flu vaccine is needed—if it’s needed,” she says.
Prevention and protection
The Centers for Disease Control and Prevention (CDC) urges us to avoid raw, unpasteurized milk and milk products. About 5 percent of Americans consume raw milk—not an insignificant number—so if you’re one of them, it would be prudent to change back to the pasteurized version for the time being.
Some states are investing in protective clothing and goggles for farmworkers.
People working with animals are advised to wash their hands frequently and wear personal protective equipment (PPE).
And finally, if you experience the symptoms described above, including conjunctivitis—a symptom associated with bird flu in both cows and humans—after being around wild birds, poultry, cows, farms or farmworkers, see your health-care provider right away.
There are 4 FDA-approved anti-viral medications for influenza:
- Oseltamivir phosphate (available as a generic drug or by the trade name Tamiflu)
- Zanamivir (Relenza)
- Peramivir (Rapivab)
- Baloxavir (Xofluza)
If your doctor determines that you have bird flu, or another type of flu that could cause serious illness, they may prescribe one of these medications.
Infectious disease specialists at Weill Cornell Medicine will continue to follow this story as it develops across the globe and in the New York Metropolitan Area.
If you have any concerns about infectious diseases, whether actual or potential, get in touch with your doctor through Connect or find a doctor here.