Another Bird Flu Variant Reaches Humans: What To Know About H5N2—After First-Ever Confirmed Death

Topline

A man in Mexico died after contracting a strain of bird flu—H5N2—that has never been seen in humans before, and is separate from the strain that is ravaging U.S. dairy cattle, the World Health Organization said on Wednesday, raising questions about the potential risks of another form of avian influenza reaching humans.

Key Facts

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What’s Different About This Strain?

Influenza is a broad family of viruses that is divided and subdivided into different types based on a variety of viral properties and can generally cause similar disease. Both H5N2 and H5N1 — the strain spreading through U.S. cattle and occasionally infecting humans at the moment — are influenza A viruses, which are known to cause seasonal human epidemics and are the only influenza viruses known to cause pandemics as well. The alphanumeric code of H and N are used to subdivide the viruses further according to what kinds of proteins are on the surface of the virus (H represents the protein hemagglutinin and N represents neuraminidase). H5 influenza primarily affects birds and can cause devastating outbreaks in wild and domestic fowl. The viruses have been known to infect other animals as well, including humans. Human cases of H5N1 are uncommon, but do happen, and Oxford University infectious disease expert Sir Peter Horby said there have been more than 900 human cases reported since 1997. For decades now, experts have widely considered the H5N1 strain to be a pathogen of pandemic potential and outbreaks, especially those that infect humans or mammals, are major public health concerns. Until the infection in Mexico, however, H5N2 was not known as a virus that could infect humans.

What We Don’t Know

As an isolated case, University of Reading virologist professor Ian Jones said “it is impossible to generalize.” There are a great deal of unknowns surrounding the H5N2 case and while certainly concerning, experts have stressed it does not give immediate cause for panic. First of all, the person who died had multiple other health conditions, which means “the role of this virus… cannot be assumed to be directly responsible (for his death) without further investigation,” said Professor Iain Brown, of Britain’s Pirbright Institute. Additionally, while officials say the source of infection is not yet known, surveillance has yet to turn up indications other humans have been infected and experts say it is still likely a spillover infection from animals. “If there are more human infections with this virus it would become of wider concern, but for now it is a very sad but isolated case,” said Ed Hutchinson, a senior lecturer at the University of Glasgow in Scotland.

Crucial Quote

“It would be reasonable to suppose this is a one-off case of zoonotic transfer with no potential to spread,” said Jones. “Unless or until there is evidence of strain adaptation or sustained transmission, the risk to the population is very low,” Jones added. “The case should act to reinforce the importance of monitoring and eradicating outbreaks in poultry as soon as they occur.”

Key Background

Avian influenza, particularly H5N1, is a major concern to health officials. It is feared as the potential source of a future pandemic, devastating to wild and domestic birds, including the food industry, and capable of spreading among mammals. In recent years, cases have been documented in wild birds and, increasingly, livestock. It has been documented in multiple mammal species as well, including sporadic human cases, and experts are concerned the virus could evolve to spread between mammals without the need for close proximity to birds, a key condition for a pandemic to take off. Outbreaks among cattle and dairy farms in the U.S. in recent months have proven particularly concerning. Increasingly, experts are starting to believe the outbreak is more serious than initially thought, particularly with evidence the virus is spreading between cows and from cows to poultry, and have criticized officials’ failure to share crucial information and lax testing requirements, which they claim risks outbreaks growing unnoticed. There have been three confirmed cases of H5N1 among dairy farm workers in the U.S., though it’s possible other cases have been missed due to a lack of testing and the possibility of asymptomatic or mild infections.

Further Reading

MIT Technology ReviewWhat’s next for bird flu vaccinesForbesBird Flu (H5N1) Explained: Study Finds First Known Case Of Mammal-To-Mammal Transnational TransmissionBy Arianna JohnsonForbesWHO Warns Threat Of Bird Flu Spreading To Humans Is ‘Great Concern’By Arianna JohnsonNytimesScientists Fault Federal Response to Bird Flu Outbreaks on Dairy Farms