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Bird flu has been around since the 1990s, detected in wild birds in China like geese; and then spreading to poultry around the world; before emerging in mammals like cows in recent months.
Bird flu is caused by a handful of influenza viruses, just like the seasonal flu that circulates each winter.
However, with the odd exception, it is spread only between animals; or from animals to humans.
Human-to-human transmission is thought to have been limited and non-sustained.
Since the 1990s, there have been 900 known human cases – nearly half have died.
Now, the World Health Organization says they have confirmed through laboratory tests the discovery of a new strain of bird flu – called H5N2 – that has never been found in a human.
It was detected in a 59-year-old man, with chronic health conditions, who died a Mexico City hospital on 24 April, a week after being admitted with fever, shortness of breath and diarrhoea.
It is unclear how he became infected with bird flu, with Mexican health officials saying he had no history of exposure to poultry or other animals.
It took officials in Mexico a month to report the case to the WHO who has only now publicly confirmed the case and lab test results (5 June).
The WHO says, at this stage, it assesses the current risk to the general population from this new strain as low, although it notes the identification of a new subtype has “the potential for high public health impact”.
Dr Wenqing Zhang is the head of the WHO’s Avian Influenza Programme.
“We need to bear in mind is that each infection in humans is an attempt of the virus to try to establish itself in human population. Although the chances are slim so far, as long as it is succeeds once, just once, it is a start of an influenza pandemic, which can be as mild as the 2009 pandemic, but equally it also could be devastating like the 1981 one also-called Spanish Flu. That’s why we are concerned about avian influenza and are watching it very closely.”
Scientists say the bird flu variant at the centre of US dairy farm outbreak, involving cows, is different to the one in the Mexico case.
Dairy workers in the US have now died from the H5N1-type of bird flu, with the first case confirmed by the WHO on 1 April.
And yet another type of bird flu is circulating among chickens in Australia – the H7N3 strain – has been detected at a fifth poultry farm in Victoria.
Victoria’s Chief Veterinary Officer Graeme Cooke says quarantine and surveillance measures are in place to contain the virus.
Veterinary scientist Robyn Alders is an honorary professor with the Development Policy Centre at the Australian National University.
She says we have yet to see sustained transmission of bird flu into a fully-fledged human pandemic, but it is the mutation of the virus that needs to be closely monitored.
“There’s been ongoing small numbers of Avian influenza outbreaks in chicken flocks in Australia since the 1970s. Those outbreaks are detected quickly because they can often cause quite high mortality in the chickens. What we are seeing now in Victoria is a little different. With the move to have pasture-raised or free-range chickens, we’re having more birds out in the open being able to have some contact with these migratory birds. And then as virus numbers increase, or the virus hitches a ride between people, birds – or things as egg trays or cages that move between different farms – the virus can hitch a ride.”
She says understanding how the variants spread and the regulations in place, is key to knowing how to respond as a consumer of milk, meat or egg products.
“So what has changed in the Australian situation is the move to having more free range flocks. What typically happens in Europe now is during the peak migratory season of birds, free range producers are asked to keep their birds inside during that time. So we may see that regulations will change here in Australia. But for consumers we should be confident that any egg or chicken, or meat, or milk product that is available for sale through the commercial outlets are safe and fit for human consumption.”
The WHO says it is preparing tailored and specific guidance to help countries develop plans to manage the public health risks.
Meanwhile, scientists are testing vaccines to protect both cows and humans against bird flu.
The US Agriculture Department is testing a vaccine developed by University of Pennsylvania researchers by giving it to calves – with the strategy of restricting the spread of the virus before it reaches dairy workers.
The US Department of Health and Human Services has also been talking to manufacturers about possible mRNA flu vaccines that, if needed, could supplement millions of bird flu vaccine doses already in government hands.
Richard Webby is a flu researcher at St Jude Children’s Research Hospital in Memphis, Tennessee.
“What the COVID-19 pandemic taught us was some of these newer technologies can be used to rapidly prepare vaccines against emerging threats like the H5 virus. And so, you know, the particular work that we’re involved in here with colleagues in Pennsylvania were actually to use that same technology that was used essentially to make a Covid vaccine, but instead of it expressing the SARS coronavirus antigens, it was expressing flu antigens.”
Scaling up vaccine development and production would require a declaration by the W-H-O that we have a virus that has pandemic potential.
Professor Alders says work on vaccines should continue – and with that strategies for prevention and preparation.
“Because of advances in science and the ability to really get excellent sequencing of the influenza virus, should it become necessary to to produce a vaccine for use in humans, that should happen relatively quickly. There are companies already looking at doing the preparatory work for developing a vaccine for use in humans. The big challenge will be as we saw in COVID, is making sure that that vaccine is available to those who really need it.”