Avian Influenza: Should We Be Concerned?

The avian influenza virus is spreading geographically, infecting new species of birds and some mammals. For the moment, human cases remain rare and no human-to-human transmission has been detected.

[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 03/04/2024.]

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 materials (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 birds could have a devastating effect on the biodiversity of our ecosystems.

 And in 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, cows. 

Although mammal-to-mammal transmission of avian influenza is supposed to be very inefficient, the outbreak of avian influenza in a mink farm in Galicia, Spain, in October 2022, is a worrying development. This is the first known outbreak documenting mammal-to-mammal transmission of a highly pathogenic strain (H5N1). The animals showed clinical signs of disease and mortality rose to 4.3%. The mink were culled and none of the workers on the farm tested positive for the virus. But it is a warning sign that this type of event could facilitate transmission of HPAI viruses to and between humans.

Photo: Dattatreya Patra / Unsplash

Can people catch avian influenza?

The risk to humans is, for now, very low. Humans can become infected only in exceptional cases and by direct contact with infected animals or their droppings, in the absence of hygienic and sanitary measures.

Globally, from January 2003 to 25 March 2024, the World Health Organisation (WHO) has recorded 888 cases of human infection with avian influenza A (H5N1) virus in 23 countries. Almost all cases of human infection have occured in Asia and are linked to close contact with infected live or dead birds, or contaminated environments. 

On January 18, 2023, WHO reported the first reported case of human infection with avian influenza A(H5) virus in the Latin America and Caribbean region: a 9-year-old girl with severe symptoms in Ecuador. The case was the seventh human infection of the current H5 clade and the third reported as severe.

The USA recently reported a human case of H5N1 (the second ever recorded in the country) in a person who had been in contact with cattle. The symptoms were mild and no infections in close contacts have been identified.

Cambodia (Prey Veng province) last year reported the death of an 11 year-old girl from avian influenza. The girl's father also tested positive for the virus, although he did not develop symptoms. The other contacts tested are negative. Genomic analysis indicates that the girl was infected with a clade of the H5N1 virus that has been circulating in the region for several years, and not the more recent clade that is circulating globally.

In Spain, two human cases of H5N1 were reported in 2022 (two asymptomatic workers at a chicken farm), but were most likely false positives.  

The risk to the general population is, at present, very low. As noted by the Spanish Ministry of Health, “the number of cases in humans remains very small compared to the total number of affected birds. And in Europe, despite the high density of factory farms, which encourage the rapid spread of the virus, animals do not typically live in areas inhabited by humans. Only people who work on farms and in contact with birds, such as veterinarians or staff responsible for disposing of affected animals, need to take precautions. Nevertheless, it is best to avoid contact with wild birds. If any sick or dead birds are found, the regional veterinary authorities should be notified so that they can remove and analyse the affected animals.

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.

Avian influenza is considered very dangerous in humans as it is much more lethal than seasonal influenza or COVID-19. In fact, more than half of the people who have been infected by the H5N1 subtype have died (888 reported infections, 462 deaths).

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

To date, there have been no reported cases of human-to-human transmission. The virus now circulating in birds does not have the capacity to spread easily from human to human. Nevertheless, we must remain vigilant in case the virus acquires this capacity through mutations. This seems unlikely, but it is possible.

Photo: Dattatreya Patra / Unsplash

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

No. So far there is no scientific evidence of avian influenza spreading via the food chain. People can catch the virus if they inhale droplets sneezed by infected birds or dust from their beds or droppings.

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.