H5N1 bird flu: What you need to know about the latest outbreak

Health agencies worldwide have been put on alert by the worst-ever outbreak of avian influenza, which has spread to other species and, in rare cases, also infected humans.

The virus, deadly to birds, especially poultry, has been causing sporadic outbreaks globally for years. However, there have been increasing reports of the virus in other wild animals. Cambodian authorities recently confirmed the death of a girl due to bird flu, a situation the World Health Organization described as “worrying”.

But what exactly is bird flu, and should we be concerned about it?

Avian influenza, or bird flu, is a highly contagious severe respiratory disease which primarily infects birds. It has a high mortality rate, especially in poultry, but doesn’t usually infect humans.

It is spread through birds’ droppings, saliva, or through contaminated food and water. Since it first emerged, it has become endemic in some parts of the world, with several strains of the virus in circulation. The current most problematic strain, H5N1, was first detected in southern China and Hong Kong back in 1996.

Outbreaks have had a devastating impact on poultry farmers, who are often forced to cull entire flocks in case of infection to stop the disease from spreading. Bird flu has led to the death and slaughter of 316 million poultry worldwide between 2005 and 2021.

However, it is not only poultry that is at risk – increasingly wild bird populations, which are responsible for much of the spread of the disease, are also becoming infected. Estimates of tens of thousands of wild birds killed by the disease are likely to significantly undercount the reality due to so few birds being tested.

And there have been a rising number of cases of bird flu detected among mammals.

Since 2003, around 860 cases of H5N1 infection in humans have been reported from 21 countries, around half of which were fatal. There have also been a smaller number of cases of infection by other strains of the virus.

The WHO points out that whenever bird flu circulates in poultry, there is a risk for sporadic infection in humans. However, the virus doesn’t currently infect humans easily, and person-to-person transmission remains unusual. Almost all cases of infection have resulted from people coming into close contact with live or dead infected birds or contaminated environments.

But with such high levels of the virus circulating, there is the risk that the virus may become better adapted to infect humans and animals. Outbreaks seen in mink farms, for example, could be particularly problematic as infections among animals living in close proximity could exacerbate this risk, the World Organisation for Animal Health warns.

The virus has been found in animals from grizzly bears to dolphins, seals, otters and foxes.

The WHO said in February that the risk to humans remains low, but the situation needs close monitoring and we must be prepared for the status quo to change.

The pandemic potential is concerning some scientists. With the virus currently circulating freely among various animal species, the chance of it mutating to become more infectious in humans is increased.

Former Wellcome director and soon-to-be WHO chief scientist Jeremy Farrar said the pandemic potential of H5N1 is a “big worry” and is one of several voices suggesting we need to do more to prepare for a potential outbreak.

“If there was an outbreak in Europe, the Middle East, America or Mexico tomorrow of H5N1 in humans, we wouldn't be able to vaccinate the world within 2023,” he says, calling on work to start on creating safe and effective vaccines.

Current seasonal flu vaccines are not effective against bird flu. But it does appear that the antiviral drug Tamiflu is effective against H5N1 in people, although there have been reports of some resistant strains. The Centers for Disease Control and Prevention in the US has also circulated with vaccine makers an H5 candidate vaccine virus which could potentially be used to produce vaccines for people.

The WHO’s flu monitoring laboratory constantly monitors circulating influenza viruses and advises on threat levels and the best response.

The World Economic Forum’s Global Health and Healthcare Strategic Outlook discusses the lessons we can take from the coronavirus pandemic and how it could shape our response to future pandemics.

“With the H5N1 bird flu virus currently circulating freely among birds and various animal species the chance of it mutating to become more infectious in humans has increased. Even though the present risk to humans remains low, we need to closely monitor the situation and prepare to respond to a potential outbreak” said Dr Shyam Bishen, Head of Health and Healthcare at the World Economic Forum.

“Currently there is no vaccine for it but we could potentially be ready to produce a H5 vaccine for use in people against H5N1. We should also consider production and stockpile of antiviral drugs such as Tamiflu which has shown efficacy against this virus in humans”, he said.

Controlling the virus’ spread is the best defence we have in preventing it from spilling over into humans.

Countries around the world have taken differing approaches to tackle the outbreak. Some countries, including China, vaccinate poultry to limit the severity and spread of the disease. But the current vaccine causes birds to test positive for the virus, which makes it tricky for farmers to know whether their flocks are infected or not.

Other countries have controlled the spread through culling and keeping poultry populations indoors to stop infection from wild birds. But with the disease so widespread currently, this is becoming untenable.

Research is also ongoing to understand which wild birds are most affected and susceptible to bird flu. This could help us better understand its spread and predict its movement as those bird populations migrate.