June 2, 2021

expert reaction to first confirmed human case of H10N3 bird flu

A 41-year-old man in China has been confirmed as the first human case of infection with a rare strain of bird flu known as H10N3.

Dr John W McCauley, WHO Collaborating Centre for Reference and Research on Influenza, The Francis Crick Institute, said:

What is bird flu? 

“There is a very wide range of influenza viruses in circulation in birds, much wider than in the main mammalian hosts of influenza: man, pigs and horses. Avian influenza viruses are particularly predominant in waterfowl and shore birds, but they are not restricted to these species. Avian flu viruses can spread between avian species and occasionally to humans and mammals.  

How is it transmitted to humans?

“Transmission to humans is usually by direct contact. The main bird flu episodes in man have been the H5N1 bird flu outbreak in Hong Kong in 1997 that was halted by closure of bird markets. In 2003 to 2004 this virus re-emerged and over the next fifteen or so years resulted in over 800 identified cases with over 400 deaths. Over this period this virus underwent evolution in birds including acquiring different neuraminidase genes, now being defined as H5Nx, and H5N8 viruses have been shown to have caused human infections recently in Russia, H5N6 viruses have also infected people.

“H7N9 viruses emerged in March 2013, and in the following four years caused over 1500 cases with over 600 deaths. These have been almost all in China.

“H9N2 virus infection of humans was first detected in 1999, and since then has tens of caused sporadic, usually mild infections.

“H10N8 have also caused a small number of human infections.

“Mostly these infections are by those in very close contact with infected birds, poultry or ducks with direct exposure whilst handling them or in preparation of meat from the infected animal.

“Once cooked, infected meat poses a very low threat.

“The new case is H10N3 in China. This is the first case of that combination in humans.

Can H10N3 be transmitted between humans and how? 

“This has not been clearly documented.

What are the symptoms in people?

“H5N1 and H7N9 infections cause serious illness – as indicated by the high mortality observed.

“H9N2 viruses are associated with mild infections.

“Conjunctivitis has been detected in some H7N7 human infections.

“The H10N3 case is currently recovering.”

Dr Nicole Robb, Assistant Professor, Warwick Medical School, University of Warwick, said:

What is bird flu? 

“Bird flu, or avian flu, is caused by influenza viruses that spread between birds. It can often spread easily between birds, but very rarely causes disease in humans.

How is it transmitted to humans?

“Most cases of bird flu in humans are caused by extremely close contact with birds or bird droppings, for example, through close-contact farming, cleaning or plucking infected birds. People can’t catch bird flu by eating cooked chicken or eggs.   

Can H10N3 be transmitted between humans and how? 

“Most avian influenza viruses aren’t transmitted easily between humans. This is because they are adapted to spread well between birds. For example:

• transmission route (bird flu is spread between birds by the faecal-oral route and so the virus is adapted to grow well in the intestinal tract of birds. The virus is less good at spreading through the air and at growing well in the human respiratory tract and so is less good at infecting humans).
• body temperature (birds have a higher body temperature than humans and so bird viruses may be adapted to grow better at higher temperatures).
• viral receptors (bird viruses may bind better to the receptors on bird cells than to the receptors on human cells, and so find it ‘easier’ to enter bird host cells).

“Bird flu viruses therefore need to acquire mutations to be able spread easily between humans. One of the most well studied changes is E627K (glutamic acid to lysine) in the viral polymerase (the viral protein that copies the viral genome), which has been shown to increase virus replication in human compared bird cells.  

“The good news is that the H10N3 bird flu virus is an ‘H10’ virus or  ‘low pathogenic subtype’, meaning that it causes few signs of disease in birds and that these viruses also very rarely cause serious disease in humans. Viruses of the H5 or H7 subtype are more worrying as low pathogenic versions can infect poultry and evolve into highly pathogenic strains which cause fatal disease in birds and can cause serious illness in humans in the rare cases that humans have been infected.

What are the symptoms of bird flu in people?

“In most cases symptoms resemble normal influenza (fever, cough, muscle aches, sore throat etc.) but it can develop into a serious respiratory illness.”

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