Avian Influenza: Should We Be Concerned?

The avian influenza virus (H5N1) is spreading geographically, infecting new species of birds and several mammal species. So far, human cases remain rare, mainly among people exposed to infected livestock or birds, and no human-to-human transmission has been detected. But this could change quickly.

[This text has been written by Yvette Moya-Angeler, communications officer at ISGlobal, and Adelaida Sarukhan, scientific writer at ISGlobal. It has been updated on 21/01/2025.]

What is bird flu?

Avian influenza is an infectious disease that affects birds. It is caused by Type A influenza viruses which belong to the Orthomyxoviridae family.

There are several strains of avian influenza virus, depending on the type of surface antigens (H and N) they present. Highly pathogenic avian influenza (HPAI) strains, including some H5 and H7 strains, are highly lethal, especially in domestic birds (geese and ducks seem to be more resistant to disease). Five subtypes (expressing H5, H7 or H9) have been reported to occasionally infect humans.

Avian influenza is highly contagious among birds and can spread from farm to farm through the movement of infected animals or contaminated equipment (products, vehicles, cages, feed, clothing, etc.). The disease can also spread by contact between migratory and domestic birds.

Why have health authorities been sounding the alarm about avian influenza?

Circulation of HPAI viruses is nothing new. However, after a period of epidemiological stability, outbreaks have been on the rise since 2020.

Increase in geographical range

In the past two years, the world has experienced an unprecedented wave of avian influenza (H5N1) that has affected -and killed - a great number of domestic and wild birds in many regions, including the Antarctica. The spread of avian influenza in wild species could have a devastating effect on the biodiversity of our ecosystems.

And a greater number of species

In addition, the H5N1 clade currently circulating worldwide has been able to jump the species barrier and infect a variety of wild and domestic mammals, including bears, sea lions, seals, big cats, racoons, ferrets, dogs, cats, and most recently, hundreds of dairy cows in the USA.

Although mammal-to-mammal transmission of avian influenza is considered to be ineffective, the outbreak of avian influenza in a mink farm in Galicia, Spain, in October 2022, is a worrying development. It is the first outbreak documenting mammal-to-mammal transmission of a highly pathogenic strain (H5N1).

Another worrying development: in March 2024, H5N1 infections were detected in dairy cows in the US. Since then, the virus has spread to a large number of herds, probably through the machinery used to milk them. More than 890 farms in 16 states have tested positive and several dozen infections have been reported in dairy workers, most of them with mild to moderate symptomatology.

Photo: Dattatreya Patra / Unsplash

Can people catch avian influenza?

The risk to the general population is, for the time being, considered low. People can become infected by direct contact with infected animals or their droppings, without hygienic and sanitary measures. Therefore, it is recommended to avoid contact with wild birds and, if any sick or dead birds are found, to notify the veterinary authorities so that they can be removed and analysed.

For people working on farms and in contact with birds or other potentially infected animals, the risk is higher, so it is recommended to take extreme precautions and use personal protective equipment.

Since January 2003 and until December 2024, the World Health Organisation (WHO) has recorded 954 human infections with avian influenza A virus (subtype H5N1) in 24 countries, and 464 deaths. Most cases have occurred in Asia and in people in close contact with live or dead infected birds or contaminated environments. In 2024, the US has reported more than 50 human infections, the vast majority of them in personnel exposed to dairy cows. Symptoms have generally been mild (mostly conjunctivitis) and no transmission to close contacts has been identified.

What are the symptoms of avian influenza in humans? Is it dangerous?

A person infected by the avian influenza virus can develop anything from a mild upper respiratory tract infection (fever and cough) to severe pneumonia, septic shock, acute respiratory distress syndrome and even death.

More than half of the people who have been infected with the H5N1 subtype have died (954 reported infections, 464 deaths). It is possible that the host, route of transmission and viral clade determine the severity of the disease. The viral genotype currently circulating in livestock appears to cause milder infections (characterised mainly by conjunctivitis) compared to that circulating in wild birds, which tend to be much more severe.

Can someone infected with avian influenza transmit the virus to another person?

At the moment there are no known cases of human-to-human transmission. The virus currently circulating in birds and livestock does not have the capacity to transmit ‘efficiently’ between humans. But the fact that it is circulating in an increasing number of mammals increases the likelihood that it will, through a few mutations, acquire the ability to do so. Close surveillance in both animals and humans is more necessary than ever.

Photo: Dattatreya Patra / Unsplash

Do I need to take precautions if I eat poultry, eggs or drink milk?

No. So far there is no scientific evidence of avian influenza spreading via the food chain. If living in an area where dairy herds are infected, it is strongly advised to avoid drinking raw milk, since it can contain live virus. Regular pasteurization, however, inactivates the virus.

Why does the virus spread so quickly from one country to the next?

Bird migration routes are thought to play a role in the geographical spread of the virus. Some studies have suggested that members of the Anatidae family (ducks, geese and swans), especially migratory ones, are natural hosts for the virus. Climate change may also play a role: if migration routes change, wild birds carrying the virus may be able to reach new territories.

The disease can also spread from one country to another through the the international smuggling of live birds.

What can we do?

We must continue to work from a One Health perspective, with the understanding that human, animal and planetary health go hand in hand. Three quarters of today’s emerging diseases are zoonotic, meaning that the pathogen jumps from an animal to a human being. Globalisation, aggression against ecosystems, invasion of natural habitats and factory farming make it ever more likely that we will continue to see outbreaks of emerging viruses.