All poultry flocks on the island of Ireland are in lockdown after a “housing order” was imposed a week ago.
This is the season for case spikes. Avian flu was detected in a small number of captive birds in Magherafelt, Co Derry, and more than 60,000 birds were due to be slaughtered last week after a suspected case was detected at a poultry operation in Co Tyrone. Given that six cases have also been found in wild birds in the Republic since December, the restrictions are prudent and probably sufficient, though with a highly infectious virus capable of jumping the species barrier, there is never room for complacency.
The Department of Agriculture and public health specialists consider the risk manageable because no other animal species is infected here. But mindful that flu ignores borders, there is concern about a high number of cases in the UK and elsewhere – and cases of human infection.
Concern has ratcheted up in the US because Type A H5N1 influenza has caused almost 1,600 outbreaks, forcing the cull of millions of birds. It has infected up to 70 people (including one fatality), with little indication its spread is under control.
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Although human symptoms are mild, there are indications of an insufficiently robust collective effort there. This conspires to heighten the risk of mutation that could lead to a pandemic.
[ Bird flu: Why are outbreaks happening and should I be worried?Opens in new window ]
Immunologist Prof Kingston Mills of Trinity College Dublin says current bird flu strains are low risk to humans, “but the big risk is another mutation that makes it transmissible among humans”.
A “scary” research article published recently showed such a mutation was possible to trigger in a laboratory situation – an exercise in trying to anticipate its virility and ability to transmit.
“There is not much evidence [human to human] is happening now but there is a risk, nevertheless,” he says. “It’s quite tricky to prevent. Every farmworker is not going to wear a mask.”
Covid-19 took hold in such circumstances; notably poor practices in Wuhan food markets where a virus soon became almost impossible to contain.
“That said, there have been remarkably few cases as [human] transmission is obviously not effective,” Mills says.
Cases of seasonal flu in humans are very high this winter but that is a different ball game, he adds – with capacity to easily crank up vaccination.
Bird flu can jump to people who have contact with sick birds and do not take required precautions, says virologist Dr Connor Bamford of Queen’s University Belfast.
“Viruses that predominantly infect birds can – and do – jump into people where they can cause severe disease and even spread to those around you. We have numerous examples of cases of bird flu in people ... so it can happen,” he says.
“If left unchecked and the virus is able to adapt to humans via more spillovers from birds to people occurring, or an outbreak in people happening, this could very well become the next pandemic,” he adds.
For several years, the H5N1 virus has been jumping from wild birds into mammals in the US (including cats, bears, raccoons and seals). Last March it was identified in dairy cows for the first time. The jump into an animal with which humans have such close contact is a serious warning sign.
As for where the next pandemic may emerge, “a lot of the betting money would be on flu”, Mills says – with the most likely route being animal-to-human transmission.
Flu is most likely because it affects so many species, where strains undergo genetic recombination to produce more pathogenic variants as time goes by.
Scientists have long considered bird flu a leading candidate for causing a human pandemic. Since 2003, it has infected at least 954 people around the world and killed at least 464, mostly in people in proximity to infected birds.
While bird flu may be relatively mild in cows, it poses a potentially greater risk to humans. That’s because, unlike birds, mammals like cows have respiratory systems more similar to humans, which could encourage mutations that make spread easier.
On whether the US bird flu strain, which is different from that in Europe, could become “a pandemic virus”, Apoorva Mandavilli, science and global health reporter at the New York Times told the Daily podcast recently this is “low risk right now”. But there is a lack of visibility on collective actions and preparedness, while updates are slow; all because of “President Trump’s dismantling of the public health system” – yet every case is another opportunity to mutate.
Virologists are watching for any sign H5N1 viruses might be adapting to grow better in humans, says Prof Ed Hutchinson of MRC-University of Glasgow Centre for Virus Research. “This would be an exceptionally unusual event, but to minimise the risk of future influenza pandemics it is crucial that situations like this are carefully monitored.”
Collaboration and clear communication between human and animal health workers is essential. It requires robust surveillance and prevention measures, such as good biosecurity on farms and contact tracing.
Research into transmission patterns and how viruses change to infect different species continues to inform preparedness efforts and identify emerging threats before they become crises, he says. This is complemented by investment in developing diagnostic tests, vaccines and drugs.
The evolution of a flu virus derived from a highly pathogenic avian influenza strain to one that is adapted to human-to-human spread is one of the most dreaded disease threats humanity faces. Fortunately, this has yet to happen during this persistent H5N1 outbreak.
