Researchers in Taiwan yesterday called on health watchdogs to keep their guard up after a flu virus strain that commonly circulates among chickens was found for the first time in a human being.
The strain was found in a 20-year-old patient from central Taiwan and although it was of relatively low virulence, it poses a risk if it mixes with other viruses and becomes more dangerous, the researchers said.
“Our report highlights the continuous need for preparedness for a pandemic of unpredictable and complex avian influenza,” they added.
Writing in the journal Lancet, a team led by Wu Ho-sheng (吳和生) from the Centers for Disease Control (CDC) reported on the case of a woman who was hospitalized in May with a fever, cough and breathing difficulties.
The agency first announced the incident in June and the publication in the peer-reviewed journal provides fuller details of its response to the case and a wider assessment of the risks it poses.
Gene sequencing of a throat swab sample taken from the patient showed that the cause of her symptoms was a local strain of the H6N1 influenza virus, the team reported.
H6N1 is a subtype of flu found among wild birds and domestic poultry on many continents.
In Taiwan, a unique genetic lineage of H6N1 has evolved over more than 40 years, previous research has found.
The local strain has shown the potential to cross-infect lab mammals, but this was the first time it had been linked to infection in a human.
The sample taken from the woman notably had a so-called G228S mutation in a surface protein called haemagglutinin that helps the virus to latch onto cells in the human host’s upper respiratory tract.
The unnamed woman recovered after being treated with the anti-viral drug Tamiflu, the study said.
When, where and how she became infected with the novel virus is unknown.
Epidemiologists tracked down 36 people who had been in contact with her, of which six developed a fever or a respiratory tract infection, but none came from H6N1.
The H6N1 patient worked as a clerk in a delicatessen, had no contact with poultry or raw meat, and had not been abroad for three months prior to contracting the infection.
Additionally, the virus strain was not detected in samples taken from two poultry farms close to her place of residence.
The discovery adds to the list of flu subtypes known to have leapt the species barrier to humans.
At present, epidemiologists are keeping a worried eye on the highly dangerous H7N9 and H5N1 subtypes, which can be transmitted from birds to humans.
However, inter-species transmission is still difficult and human-to-human transmission is rarer still.
Despite this, the worry is that the viruses could acquire genes that make them more infectious and lethal, developing into a new pathogen people have no immunity against.
One well-known intermediary for this so-called genetic reassortment is the pig. Pigs can simultaneously carry avian, human and porcine viruses, effectively providing a “kettle” to allow viruses to swap genes.
Three influenza pandemics have occurred in the 20th century, killing tens of millions of people. The first flu pandemic of the 21st century occurred in 2009 with the H1N1 subtype, which turned out to have approximately the same lethality as ordinary “seasonal” influenza.
“Our findings suggest that a unique group of H6N1 viruses with the human adaption marker G228S have become endemic and predominant in poultry in Taiwan,” Wu said.
“As these viruses continue to evolve and accumulate changes, they increase the potential risk of human infection. Further investigations are needed to clarify the potential threat posed by this emerging virus,” he added.