A type of avian flu has infected people for the first time. So far, the virus doesn鈥檛 seem to be especially threatening, but its jump from chickens to humans was unexpected: the World Health Organization says no similar strains have ever crossed over to people before.
Last week, the announced that a 68-year-old woman in Jiangsu Province in eastern China was hospitalised in January with severe respiratory symptoms. This turned out to be the first recorded case of an H7N4 flu virus infecting humans. The woman recovered after a month in hospital.
But the case still rang alarm bells, highlighting the huge amount of unpredictable viral evolution taking place in livestock farming. A different kind of bird flu 鈥� H7N9 鈥� first emerged in China in 2013, and has since infected more than 1,500 people there. More than half of these cases took place last winter and spring alone, and .
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H7N9 has become ubiquitous in Chinese poultry, but it doesn鈥檛 spread easily from person-to-person. The nightmare scenario is that this virus could hybridise with a type of influenza that spreads more readily between people, and cause a severe pandemic. Such hybridisation can occur when one bird carries two or more kinds of flu 鈥� and it seems that .
Virus evolution
Flu viruses are named after two particular proteins they carry on their surface 鈥� H and N. These have a variety of forms, and it may have been possible that the Jiangsu H7 had come from the H7N9 flu hybridising with another strain.
But Wenqing Zhang of the World Health Organization says gene sequencing shows the virus鈥檚 H7 is most closely related, not to H7N9, but to viruses sampled from birds in South Korea a year ago, which have never been known to infect people before. The surface protein that binds to cells works better in birds than humans, so unless it starts adapting to mammals, H7N4 shouldn鈥檛 spread any further.
The infected woman had handled live poultry before falling ill, so probably caught the virus from聽birds or the market she bought them in. No one around her developed any symptoms. But this is still a warning. 鈥淭his case reminds us that virus activity in animal reservoirs is very dynamic, and we should not just focus on one subtype,鈥� says Zhang.
However, we are not testing enough flu in its animal hosts to spot potentially threatening strains. We can only detect problem flu after it infects people.
While some birds are tested for flu strains, other livestock is barely monitored at all. 鈥淪ampling wild birds and poultry shows us only a tiny part of the tip of the iceberg,鈥� says , of the Research Centre for Emerging Infections and Zoonoses in Hannover, Germany. There is no published monitoring of flu in pigs, which can also produce hybrid flu viruses, such as the pandemic swine flu of 2009.
New year celebrations
鈥淭he solution to the flu problem will be knowing virus evolution well enough so we can make human countermeasures before a virus spreads in humans, not after, like now,鈥� says Zhang. Such countermeasures would include vaccines, if we can catch new viruses early, and make vaccines fast enough. However, that will require new technology, says Zhang.
Meanwhile, H7N9 remains a concern. Last year it acquired a mutation that lets it spread more aggressively in poultry. Last October, China launched a nationwide poultry vaccination campaign, and this may reduce human exposure to the virus.
But flu can spread silently in vaccinated poultry, so vaccination might also give it new opportunities to evolve. Worryingly, found that H7N9 mutations had allowed limited spread among mammals.
There could be more surprises in store, as thousands of people travel and eat freshly-slaughtered chicken for Chinese New Year. This could increase the risk that novel bird flu strains will cross over into humans and spread further.
Given the dozens of flu viruses now circulating in people and chickens in China, flu may yet carry more surprises for the Year of the Dog.
Read more: Waiting for the big one: A new flu pandemic is a matter of time
