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Explained | What does the World Health Organisation say about H10N3 bird flu, and is there a reason to worry?

The story so far: China has confirmed the first instance of human infection from H10N3, a rare strain of a virus that normally infects poultry. On Tuesday, the National Health Commission of Beijing reported that a 41-year-old man in the eastern Jiangsu province had been infected with the rare strain but no details were given as to how he caught it.

What do we know so far about H10N3?

Chinese authorities said the 41-year-old man was the first human case of an infection with the strain. They said the person was hospitalised on April 28 and was diagnosed with the strain after a month. The Beijing-based National Health Commission said the strain has low pathogenesis — the ability to cause disease — among birds, implying that the virus did not spread easily among poultry and was likely to be restricted to limited populations. “As long as avian influenza viruses circulate in poultry, sporadic infection of avian influenza in humans is not surprising, which is a vivid reminder that the threat of an influenza pandemic is persistent,” Reuters quoted the World Health Organization (WHO) as saying.

What is avian influenza?

H5N1 is the most common virus causing bird flu, or avian influenza. Though largely restricted to birds, and often fatal to them, it can cross over to other animals, as well as humans. According to the WHO, the H5N1 was first discovered in humans in 1997 and has killed almost 60% of those infected. Though it is not known to transmit easily among humans, the risk remains.

There are several subtypes of the avian influenza virus. Since 2003, these avian and other influenza viruses have spread from Asia to Europe and Africa. In 2013, human infections with the influenza A(H7N9) virus were reported in China. An outbreak of the H7N9 strain killed around 300 people in 2016 and 2017. The U.S. Centers for Disease Control and Prevention says, “All known subtypes of influenza A viruses can infect birds, except subtypes H17N10 and H18N11, which have only been found in bats. Only two influenza A virus subtypes (i.e., H1N1, and H3N2) are currently in general circulation among people. Some subtypes are found in other infected animal species. For example, H7N7 and H3N8 virus infections can cause illness in horses, and H3N8 virus infection cause illness in horses and dogs.” So far, the H10N3 appears mild and not very transmissible, and hence, its categorisation status remains unclear.

What are the typical symptoms of an avian influenza infection?

According to the WHO, avian, swine and other zoonotic influenza virus infections in humans may cause disease with symptoms like mild upper respiratory tract infection (fever and cough), early sputum production and rapid progression to severe pneumonia, sepsis with shock, acute respiratory distress syndrome, and even death. Conjunctivitis, gastrointestinal symptoms, encephalitis and encephalopathy have also been reported in varying degrees depending on the subtype.

Why are bird flu viruses a cause of concern?

Speculation about the origin of the SARS-CoV-2 has heightened worries about animal- and bird-borne viruses. The emergence of new strains, particularly among domesticated animals and birds, is a story of evolution and inevitability, and sporadic reports of new viruses infecting humans abound. An outbreak of the H5N8 virus in birds led to hundreds of thousands of poultry being culled in various European countries. In February, Russia reported that seven poultry workers in a plant were infected by the H5N8 strain. All of them recovered. India, too, faced an outbreak of the virus in flocks of poultry in January and undertook culling.

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