The following outbreaks, which occurred last year, illustrate the reality of zoonotic influenza, the fact that all ages can be vulnerable, that those with and without comorbidities can be at risk, and that various exposures can lead to avian influenza infection. It is interesting to note the way scientists are able to analyse the viruses and fit them within a phylogenic tree showing their relationships and evolution. The diversity of zoonotic influenza viruses that caused human infections in 2023 is alarming and infections of some types of zoonotic influenza viruses caused severe disease with a high mortality rate. In 2023 they did not transmit easily from person to person, although we never know when this may change, and therefore must be ever-ready for a pandemic.

WHO will continue to strengthen surveillance, jointly with its partners, in both animal and human populations, thoroughly investigate every zoonotic infection, build up pandemic preparedness planning, and get better readiness for the next influenza pandemic. Here is a summary of some avian influenza outbreaks notified to WHO last year:

Ecuador

On 9 January 2023, WHO was notified of a human infection caused by an avian influenza A(H5) virus. The case, a nine-year-old girl, living in a rural area in the province of Bolívar, Ecuador, was in contact with backyard poultry a week before the onset of her symptoms. As of 18 January she was hospitalized, in isolation, and being treated with antivirals. This was the first reported case of human infection caused by avian influenza A(H5) virus in the Latin America and the Caribbean region. Work was ongoing to further characterize the virus.

Find out more about this outbreak here.

Cambodia

On 23 February 2023, WHO was notified of one confirmed case of human infection with avian influenza A (H5N1) virus. The case was an 11-year-old girl from Prey Veng province, in the south of Cambodia. The patient passed away on 22 February 2023. Virus sequencing showed the H5N1 virus belonged to clade 2.3.2.1c, and similar to the viruses circulating in poultry in southeast Asia since 2014. A second case, the father of the first case, was reported on 24 February 2023. However, as of 26 February he was asymptomatic and in isolation at the referral hospital. An outbreak investigation was ongoing including determining the exposure of these two reported cases to the virus.

Find out more about this outbreak here.

Chile

On 29 March 2023, WHO was notified of a laboratory-confirmed case of human infection caused by avian influenza A(H5) virus in the Region of Antofagasta in the north of Chile. The patient was a 53-year-old male. He had no history of comorbidities or recent travel. On 13 March 2023, he developed symptoms including cough, sore throat, and hoarseness. On 21 March, due to worsening symptoms, he sought care at a local hospital and the following day was transferred to a regional hospital. On 23 March, he was admitted to the intensive care unit. On 24 March, treatment with antivirals (oseltamivir) and antibiotics was initiated. As of 21 April, he remained in respiratory isolation under multidisciplinary management, with mechanical ventilation due to pneumonia.

This was the first human infection with avian influenza A(H5) virus reported in Chile and the third reported in the Region of the Americas to date. Avian influenza A (H5N1) was first detected in the Americas in birds in December 2014. Between December 2022 and February 2023, highly pathogenic avian influenza (HPAI) was detected in wild aquatic birds (pelicans and penguins) and sea mammals (sea lions) in the Antofagasta Region where the case resides. According to preliminary findings of the epidemiological investigation of this human case, the most plausible route of transmission was through environmental exposure in areas close to the residence of the case where either sick or dead sea mammals or wild birds were found. Genomic sequencing identified the virus as avian influenza virus A(H5N1) from the phylogenetic clade 2.3.4.4b. The genomic sequencing had 99.9% identity with H5 hemagglutinin sequences from Chilean birds.

Find out more about this outbreak here and here.

China

On 27 March 2023, WHO was notified of one confirmed case of human infection with an avian influenza A(H3N8) virus. The patient was a 56-year-old female from Guangdong province with an onset of illness on 22 February 2023. She was hospitalized for severe pneumonia on 3 March 2023 and subsequently passed away on 16 March 2023. The patient had multiple underlying conditions. She had a history of exposure to live poultry before the onset of the disease, and a history of wild bird presence around her home. Results of testing showed that the samples collected from a wet market, where the patient spent time before the onset of illness, were positive for influenza A(H3). This was the third reported case of human infection with an avian influenza A(H3N8) virus; all three cases have been reported from China.

Find out more about this outbreak here.

United Kingdom of Great Britain and Northern Ireland

In mid-May, WHO was notified of the detection of avian influenza A(H5) virus in a poultry worker at a farm in England where poultry was infected with A(H5N1) virus. Another detection was reported in a second individual performing culling operations on the farm. Both detections were later confirmed by additional testing. Both cases were asymptomatic and detected as part of an ongoing enhanced surveillance study of asymptomatic workers exposed to poultry infected with avian influenza.

Find out more about this outbreak here.

Cambodia

Between 24 and 25 November 2023, WHO was notified of two confirmed cases of human infection with influenza A(H5N1) from the same village in Kampot Province. Both cases were female, one in the 20-25 years age group and the other less than five years old. The first case died, while the second was being treated in hospital as of 29 November. Both cases had exposure to backyard birds, which were reported to be sick, with some having died, over the prior month. In total, six cases of influenza A(H5N1) were reported from Cambodia in 2023. Laboratory investigation shows the viruses, as indicated by phylogenetic analysis, fall within the H5 clade 2.3.2.1c with close similarity to the viruses that have been circulating in Cambodia and Southeast Asia since 2013-2014.

Find out more about this outbreak here.