What To Know About Bird Flu, Including the H10N3 Strain

Here's why you don't need to be worried about the strain, according to infectious disease experts.

In June 2021, China's National Health Commission (NHC) announced that a 41-year-old man in the city of Zhenjiang, in the Jiangsu province, was infected with the H10N3 strain of bird flu, according to a Reuters report. It was the first case of a human infection with H10N3.

The NHC said that man was hospitalized on April 28, 2021, after developing a fever and other symptoms, but he wasn't diagnosed until Friday, May 28, 2021. Fortunately, he was stable enough to be discharged from the hospital, and other infections weren't detected among his close contacts, per Reuters. The NHC said the chances of large-scale spread of the H10N3 strain were low, according to Reuters.

H10N3 bird flu
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With public health anxiety at an all-time high due to the COVID-19 pandemic, it's understandable why news of another new virus detected in a human was alarming. But luckily, this virus did not turn out to be a widespread threat.

As of May 2022, the Centers for Disease Control and Prevention (CDC) reported that H10N3 had only affected one person in China in 2021, and no other cases were reported. Similarly, the World Health Organization has reported this 2021 case as the only human infection of H10N3.

Here's what you need to know.

What Is H10N3?

H10N3 is a form of avian influenza—aka "bird flu"—the CDC reports. These viruses normally infect wild aquatic birds, as well as domestic poultry and other bird and animal species, but they don't normally infect humans. Rare cases of other strains of avian influenza have been reported, according to the CDC.

In those rare cases, saliva, mucous, or feces from infected birds get into a person's eyes, nose, or mouth. These infections have occurred after unprotected contact with infected birds or surfaces contaminated with avian influenza viruses, the CDC says.

As far as the new H10N3 strain goes, because it's only been reported in one person, there isn't much information on it right now, Waleed Javaid, MD, director of infection prevention and control at Mount Sinai Downtown in New York, told Health shortly after the report was released. "We know very little because there's only been one reported case at this time," said Dr. Javaid at the time, though he added that the strain appeared to have been circulating among birds for a while.

Expert Opinions About H10N3

Since there were no other cases of H10N3 among the patient in Zhenjiang's close contacts, we don't know if H10N3 can be spread via human-to-human transmission, Dr. Javaid said at that time. However, while it was still too early to say definitively that it can't be spread between humans, the fact that the individuals the patient had come in contact with didn't show signs of having been infected with the strain was considered good news.

If human-to-human transmission of H10N3 was a huge threat, we'd likely see far more cases right now, said Dr. Javaid at that time.

Given what we know right now—that only one person has been infected—we don't need to sound any alarms. "One case—probably too premature to start worrying about it," said Dr. Javaid, who added that the CDC hadn't issued any sort of warning about the strain.

Other Avian Influenza Virus Infections

Currently, there are a few avian influenza strains known to infect humans: H5, H7, and H9—usually in the form of H5N1 and H7N9 viruses, per the CDC.

And while they're rare in the general population, these infections happen most often among those who work with poultry, Amesh Adalja, MD, senior scholar at Johns Hopkins Center for Health Security, told Health. "They are often one-off infections," Dr. Adaja said.

According to the European Centre for Disease Prevention and Control, the first human cases of the H5N1 virus infection were identified in Hong Kong in 1996—and while a small number of health care workers and household contacts got infected with the virus, it didn't spread any further.

Smaller clusters have been found periodically throughout Asia since, and more than 700 human infections globally have been reported to the World Health Organization (WHO) since November 2003, according to the CDC. Though these human infections are rare, about 60% of cases prove fatal, per the CDC.

The first human infections of the H7N9 strain were reported to the WHO in March of 2013, the organization reports, adding that those infected had been in contact with "animals or with an animal environment." According to an update from the WHO posted in September of 2018, among 1,567 laboratory-confirmed cases of the strain, there were 615 deaths.

Overall, per the CDC, "Asian H5N1 and Asian H7N9 viruses have not been detected in people or birds in the United States."

It's also important to remember that context is key regarding bird flu strains, Dr. Adalja said, adding that infectious disease experts are constantly monitoring for new strains that might pose a public health threat. That said, it's possible that this one case of the H10N3 strain will be the only human case of the infection—but only time will tell, said Dr. Javaid. As it turns out, Dr. Javaid was right.

Symptoms of Avian Influenza

Just generally speaking, based on what experts know about bird flu overall, the symptoms often look like a typical influenza-like illness ranging from mild to severe infections, per the CDC. That means symptoms can include:

  • Conjunctivitis
  • Influenza-like illness (fever, cough, sore throat, muscle aches)
  • Nausea
  • Abdominal pain
  • Diarrhea
  • Vomiting
  • Severe respiratory illness (shortness of breath, difficulty breathing, pneumonia, respiratory failure)
  • Neurologic changes (altered mental status, seizures)

Avian influenza viruses, however, cannot be diagnosed by signs and symptoms alone—the CDC says laboratory testing is needed, usually through swabs collected from the upper respiratory tract of an infected person.

As for treatment of avian influenza viruses, the CDC recommends what's known as a neuraminidase inhibitor—like oseltamivir, peramivir, and zanamivir—a type of antiviral drug that can block reproduction of the virus. And the best way to avoid avian influenza viruses is to avoid exposure, which includes direct or close contact with infected poultry (though, again, that is not an issue in the US).

Studying the Virus

Because the strain is "not a very common virus," as Filip Claes, regional laboratory coordinator of the Food and Agriculture Organization's Emergency Centre for Transboundary Animal Diseases at the regional office for Asia and the Pacific, told the Associated Press that experts would have to analyze the genetic data of the virus to see if it resembles old viruses or if it's a brand-new mix.

But right now, since experts aren't concerned about wide-scale spread, and because they don't know if the virus can be spread via person-to-person contact, there's nothing to be worried about at this time, said Dr. Javaid shortly after the June 2021 NHC report. "Knowing about this is important," Dr. Javaid explained, "[but] right now, it's more of a wait, watch, and see," added Dr. Javaid.

Thankfully, things turned out well and there wasn't an outbreak—only one person was infected, per the WHO.

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