Avian flu A-H5N1: symptoms, risks for humans?

We are talking about A H5N1 virus during avian flu epidemics affecting animal farms in France. No cases in humans have been diagnosed in France to date but a 65-year-old man died from this virus in the United States in January 2025. Human cases of this avian flu have already been recorded in China. What exactly is it? What are the risks for humans? What symptoms? Insights with Professor Jeanne Brugère-Picoux, veterinarian specialist on the subject.

What is A-H5N1 avian flu?

We are talking about flu Has H5N1 but we should actually talk about highly pathogenic avian influenza H5N1. “Avian plague is primarily an animal disease, highly contagious, caused by influenza type A viruses, which can infect many species of domestic and wild birds.“defines ANSES.”H5N1 avian plague comes from wild water birds during migrations which cannot be slaughtered, unlike farmed birds” continues our interlocutor. We can distinguish:

► Low pathogenic avian influenza viruses (LPAI)

► Highly pathogenic avian influenza viruses (HPAI), including subtypes H5 or H7.

When the infection is due to an HPAI virus, in a susceptible species, it is classically “avian plague”. Avian “flu” being a term to be reserved for human disease caused by viruses of avian origin or “chicken flu”.

Origin and appearance of the H5N1 virus

“This virus originated from influenza A viruses which spread mainly via migratory wild birds in many parts of Africa, Asia and Europe” underlines Professor Jeanne Brugère-Picoux. This virus was detected for the first time in a domestic goose in the Guangdong province in South China in 1996. One year later, an epidemic of avian plague H5N1 broke out in domestic poultry in Hong Kong which infected 18 humans and caused the death of 6 people. This viral disease is spotted again in 2003 in poultry first in Asia then in Europe and Africa, affecting animal species then hundreds of human cases, causing numerous deaths. Other viruses of the same H5N1 subtype have been responsible for epidemics in French breedings in 2021-2022 and 2022-2023.

What are the risks for humans?

Avian flu can be transmitted from animals to humans directly from birds or contaminated environments with which humans are in contact or through an intermediate host, for example a pig. “I do not believe in a pandemic of avian flu with this virus in humans” says the veterinarian. “The virus is not adapted to humans, she continues. The disease is essentially animal. Apart from human cases recorded in China, most probably linked to poor hygiene conditions, there has never been human-to-human transmission.. We must be wary of sick wild birds, but we are not in the habit of eating raw poultry or touching a sick bird. The only risk actually lies in the mutation of the virus. For example, if it contaminates a pig then a human, but mixed pig and poultry farms are closely monitored to prevent viruses from spreading.“For her”it is necessary to be vigilant in monitoring the evolution of these avian plague viruses and their zoonotic potential even if the hypothesis of a pandemic linked to such a virus is fortunately far from being demonstrated.

Mild symptoms in humans

In animals, the H5N1 virus causes very high mortality (around 50%). In humans, “the clinical forms ranged from mild or even asymptomatic symptoms to severe forms with admission to intensive care and death. indicates Public Health France. It manifests itself a priori as a flu syndrome with:

• conjunctivitis
• encephalitis
• upper respiratory tract infections (fever and cough)
• sputum that can progress to serious pneumonia
• acute respiratory distress syndrome
• septic shock
• gastrointestinal symptoms (nausea, vomiting, diarrhea)
• the death

What is the incubation period of the virus?

In human cases observed sporadically in Asia with H5N1 avian plague virus, the WHO has estimated an incubation period of 2 to 17 days.

► Do not touch dead or injured animals and report them to the Departmental Biodiversity Office or the Hunters’ Federation and inform the town hall;
► Protect yourself individually (gloves, mask, hand washing) in the event of contact with wild avifauna such as the collection of dead wild birds or during professional exposure to birds suspected of infection;
► Get vaccinated against seasonal flu every year if you are a professional exposed to swine and avian influenza viruses. A simultaneous infection with an avian or swine influenza virus and a human influenza virus could indeed lead to the emergence of a new influenza virus contagious to humans;
► Consult your doctor immediately if you experience symptoms. (fever, cough, fatigue, breathing difficulties, neurological disorders), within 10 days following risky exposure (contact with wild or domestic birds, with sick or dead wild mammals, or with flu-infected pigs).

“For health professionals: it is requested to immediately report any suspected case of zoonotic influenza to the health authorities in order to classify or not the patient in a possible case and to put in place appropriate management measures” adds the Agency.

There is no vaccine against H5N1 flu

There is no no vaccine against the H5N1 virus in humans. “There are two antivirals effective against influenza or avian viruses. They can be used for curative or preventive treatment. In the pandemic context, these antivirals are used above all to protect health personnel and professions whose continued activity is essential to ensure the functioning of national structures.” notes the Pasteur Institute. “Laboratories are working on a vaccine that could include the A H5N1 virus for poultryespecially ducks which are more often outdoors” underlines our expert. At the request of the European Commission, EFSA examines vaccination strategy against highly pathogenic avian influenza virus. “The conclusions of this work, in which the European Medicines Agency (EMA) and the European Union Reference Laboratory also participate, will be available during the second half of 2023” indicates the EFSA.

Thanks to Professor Jeanne Brugère-Picoux, veterinarian, Honorary Professor of the National Veterinary School of Alfort, member of the National Academy of Medicine.