2020–2023 H5N1 outbreak

During 2020, reassortment, genetic "swapping" involving the swapping of DNA or RNA, between poultry and birds, led to the emergence of H5N1. The virus then spread across Europe, detected there in autumn, before spreading to Africa and Asia.[1]

In May 2021, H5N1 was detected in wild red foxes in the Netherlands.[5] It was later detected in December in Estonia in wild foxes.[1][6]

In January 2022, an infection in an eighty-year-old man was reported, who raised ducks in England.[1] Also in January, infections were reported from the United States in wild birds.[1] In February, infections were reported from commercial poultry centres in the U.S., and Peru reported infections in sea lions.[1][7] A human case of H5N1 was reported in the U.S. in April.[1][8] The virus continued to spread further, infecting additional species of mammals. In September, Spain reported a human case; this was followed by a second case, in a person who worked at the same poultry farm as the first.[1][9] In November, China reported a human case, infected due to contact with poultry. The case died from their infection.[1]

In February 2023, Cambodia reported the death of a girl due to H5N1 infection after developing symptoms on 16 February.[10][11] The girl's father also tested positive for the virus. The World Health Organisation described the situation as "worrying" and urged "heightened vigilance".[12][13][14] Further sequencing determined that at least one of the two cases was from an older H5N1 clade, 2.3.2.1c, which had circulated as a common H5N1 strain in Cambodia for many years, rather than the more recent clade 2.3.4.4b, which had caused mass poultry deaths since 2020. This older clade had jumped to humans in the past yet hadn't previously resulted in any known human-to-human transmission.[15]

On March 1, 2023, as Taiwan raised its travel alert for Cambodia, the WHO and the U.S. CDC, in concert with Cambodian authorities, determined that both of the individuals had been infected through direct contact with poultry.[16][17]

In late February 2023, Argentina confirmed a case of H5N1 in industrial poultry, in the Rio Negro province. Avian product exports were suspended as a result.[18]

In March 2023, H5N1 was detected in black-necked swan populations in Carlos Anwandter Nature Sanctuary, Chile and Uruguay.[19][20] In Uruguay the death of ten swans found in the locality of Estación Tapia was attributed to flu.[20] Previously in Uruguay ten hens had died because of the flu in El Monarca.[20]

In late March 2023, Chile detected H5N1 in a 53 year-old man who had severe symptoms.[21]

In September 2023, Uruguay reported upwards of 400 seals and sea lions found dead of H5N1 on the nation's Atlantic coastline and along the River Plate.[22]

On April 1 a domestic dog in Ottawa, Canada was tested positive for H5N1.[23]

On May 22, Brazil declared an 180-day "animal health emergency" in response to eight cases of H5N1 found in wild birds. Although Brazil's major poultry-producing regions are in the country's south and the infections were found in Espirito Santo state and Rio de Janeiro state, Brazil, as the world's largest exporter of chicken meat, created an emergency operations center to plan for and mitigate potential further spread of H5N1.[24]