Highly pathogenic A(H5N1) bird flu first appeared in southern China in 1996. The next year, large outbreaks in poultry led to 18 human infections.
The virus was not controlled and re-emerged in 2003, spreading widely across Asia. Over time, A(H5N1) reached Africa, Europe, and the Middle East.
Since 2020, 91 human cases of highly pathogenic bird flu have been reported worldwide. Here’s what to know about the outbreaks in affected locations.
2020: Major Bird Flu Outbreaks Drive Global Infections
In March 2020, LPAI H7N3 and HPAI H7N3 outbreaks hit U.S. turkey farms. That year, gene-swapping between poultry and wild bird viruses led to HPAI H5N1. This new strain carried an N1 NA gene from wild birds.
Wild bird-adapted HPAI H5N1 first appeared in Europe in fall 2020. It then spread to Africa, the Middle East, and Asia. In 2020, China reported five human cases of HPAI H5N6.
The Ministry of Health in Laos reported a human case of A(H5N1) bird flu. The patient was a one-year-old girl.
She developed a fever, cough, breathing issues, and runny nose on October 13, 2020. The patient was hospitalized on October 16 and discharged on October 19.
As part of routine surveillance, doctors collected a specimen at admission. On October 28, tests confirmed A(H5N1).
In December 2020, Russia found HPAI H5N8 in an asymptomatic poultry worker. Also in 2020, Hong Kong reported LPAI H9N2 in a child with moderate illness. The child may have had indirect exposure to backyard poultry.
In 2020, China reported five LPAI H9N2 cases. Four children and one adult had mild illness, detected through ILI surveillance.
2021: China Sees Escalating Infections
In March 2021, Laos confirmed its first human HPAI H5N6 case. A child became mildly ill in February after contact with infected poultry.
Also in May, China reported the first human LPAI H10N3 case. An adult became critically ill but recovered. The only known exposure was visiting a live poultry market.
In June 2021, China confirmed its first human infection with LPAI H10N3. Throughout 2021, China reported 36 human cases of HPAI H5N6. Eighteen of these cases were fatal.
China also identified 24 human cases of LPAI H9N2. Nineteen mild cases occurred in children, and two mild cases in adults. Three adults had severe illness, and one died.
On July 21, 2021, India reported its first human A(H5N1) case to WHO. The patient was a boy under 18 from Haryana state. He had an underlying illness diagnosed in June 2021.
Shortly after starting immunosuppressive treatment, he developed fever, cough, and breathing issues. His condition worsened to acute respiratory distress syndrome. He was put on a ventilator but died on July 12.
2022: A Serious Increase in Cases Worldwide
In January 2022, an 80-year-old man in England tested positive for HPAI H5N1. He raised ducks that became sick in late December 2021 but showed no symptoms.
In April 2022, the U.S. reported its first human HPAI H5N1 case. Contamination of nasal passages may have caused the positive test.
Also in April, China confirmed the first human LPAI H3N8 case. Between January and April 2022, China reported seven human HPAI H5N6 cases. All patients had severe or critical illness, and one died.
China also reported four LPAI H9N2 cases—three in children and one in an adult. All had mild illness.
Between May and September 2022, China reported four severe human HPAI H5N6 cases. One patient died.
In May, China confirmed an LPAI H10N3 infection in a man with no known poultry exposure. He became critically ill but recovered.
In September, Spain reported a human HPAI H5N1 case in an asymptomatic poultry worker. In November, a second case was reported at the same farm.
In October, Vietnam reported a severe HPAI H5 case in a child after backyard poultry exposure.
Between October and November, China reported four LPAI H9N2 cases. Three were mild in children and one was severe in an adult.
In November, China reported a fatal HPAI H5N1 case in an adult with poultry exposure.
2023: Bird Flu Infection Rates Slow, But Persist
In January 2023, Ecuador documented its first human HPAI AH5 infection. The patient was a child who became critically ill after exposure to backyard poultry.
In February, Cambodia recorded two human HPAI H5N1 cases. One of the cases was fatal.
Preliminary sequencing showed Cambodia’s viruses were clade 2.3.2.1c. This differs from the H5N1 viruses circulating in the U.S. and other countries.
Between February 2023 and August 2024, 16 human cases were verified in Cambodia. Investigators found all patients had contact with sick poultry or poultry environments. At least three of the patients died from their infections.
2024: First U.S. Death from Bird Flu
On April 1, 2024, a person in the U.S. tested positive for H5N1. This was the first reported case of cow-to-human transmission of the virus.
In May, the CDC reported two more H5N1 human cases in Michigan. The second case was confirmed on May 22, and the third on May 30. Both had exposure to infected dairy cows.
On July 3, 2024, the CDC confirmed the fourth U.S. H5N1 human case. The patient had contact with infected cows in Colorado.
On August 20, 2024, Cambodia reported a human A(H5N1) case to WHO. The patient was a 15 -year-old from Prey Veng Province with no health conditions. She developed a fever on August 11 and was hospitalized on August 17 in Phnom Penh.
On December 18, 2024, a patient was hospitalized in Louisiana with severe H5N1 bird flu. This marks the first severe H5N1 case in the United States. The CDC confirmed the infection on December 13, 2024.
Genetic analysis shows the virus belongs to the D1.1 genotype. This genotype has been found in recent cases in Canada and Washington state.
The patient in Louisiana later became the first U.S. patient to die from bird flu. The United States has detected 68 human H5N1 cases since 2024.
Conclusion
H5N1 bird flu continues to spread among animals and infect humans worldwide. Most human cases are linked to direct exposure to infected poultry or livestock. Ongoing surveillance and safety measures remain crucial to prevent further infections.
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Logan Hamilton is a health and wellness freelance writer for hire. He’s passionate about crafting crystal-clear, captivating, and credible content that elevates brands and establishes trust. When not writing, Logan can be found hiking, sticking his nose in bizarre books, or playing drums in a local rock band. Find him at loganjameshamilton.com.
