International Events

Influenza Transmitted from Animals to Humans Risk Review and Assessment (Third update - April 13, 2023)

  • New Infections: A case of influenza A (H3N8) virus was reported on 27 March 2023 in China, which is the third reported case of human infection with influenza A (H3N8) virus, all in China. (details in Section C)
  • Risk Assessment: The overall risk to public health from currently known influenza viruses at human-animal interaction has not changed, and the potential for human-to-human transmission of these viruses remains low. Human infections with viruses of animal origin are also expected in places where these viruses spread in animals.
  • International Health Regulations: All human infections caused by a new influenza subtype must be reported under International Health Regulations (IHR, 2005). Information from these notifications is critical to enrich animal-to-human risk assessments of influenza.
Avian influenza viruses
  1. Avian influenza A (H5) viruses
    • November 11th, 2022 to January 5th, 2023
Since the last risk assessment on November 11th, 2022, a human case of influenza A (H5N6) virus was reported in China on November 23. The case is of a 54-year-old male from Hunan Province. He had started falling ill on November 2, 2022 and was admitted to hospital on November 5 in critical condition with pneumonia. He worked in a restaurant preparing food. The source of exposure to the virus has not been determined. No other cases were reported among family members (1).​

  • January 6th, 2023 to February 26th, 2023

On January 9th, 2023, Ecuador reported a human case of avian influenza A (H5) virus. The case is of a 9-year-old girl, with no known comorbidities, from Bolívar Province, Ecuador, who presented with conjunctival pruritus and coryza on December 25th, 2022. On December 27th, due to persistent symptoms including nausea, vomiting and constipation, she was admitted to the General Hospital, On January 3rd, 2023, she was transferred to a children's hospital in critical condition; She was admitted to the intensive care unit after developing septic shock due to pneumonia. The results came back positive for influenza A virus (H5) on January 5th. According to the epidemiological investigation, the family's poultry died for no apparent reason a week before the onset of symptoms. Epidemiological investigations also revealed a number of poultries that died in the same community in which the family resided. Contact tracing was conducted, and it was reported that there were no other cases detected among the contacts in this case (2).

On February 23rd, 2023, Cambodia's International Health Regulations (IHR) National Focal Point reported one confirmed case of human infection with avian influenza A (H5N1) virus to WHO. The case is of an 11-year-old female from Pre Vieng Province in southern Cambodia. On February 16th, 2023, the case developed symptoms and received treatment at a local hospital. On February 21st, 2023, the case was admitted to Children's National Hospital with severe pneumonia. A sample was collected and tested positive for avian influenza A (H5N1) virus. The patient died on February 22nd, 2023. Samples were collected and tested from all contacts. Laboratory tests also confirmed that the second case, on February 23rd, 2023, was the father of the infected child, who did not show symptoms, and was isolated in the referral hospital (3).

According to reports received by World Organization for Animal Health (WHAO), different subtypes of influenza A (H5) are still being detected in birds in Africa, Asia, Europe and North America. The recent detection of A (H5N1) virus has been reported by several countries in Central and South America and Africa. Since 2021, Europe is experiencing the largest epidemic of highly pathogenic avian influenza viruses ever observed in wild and domestic birds and over such a wide geographic scale (1).

   2. Avian influenza viruses A(H9N2)

Since the last risk assessment on November 11th,  2022, three human cases of influenza A(H9N2) virus infection were reported from China on 23 November 2022 (Table 1). All three cases were discovered in surveillance of an influenza-like illness and the cases are unrelated. No other cases were reported among the family members of the cases (1). 
Avian influenza virus A(H9N2) is endemic in poultry in Asia and is increasingly being reported in poultry in Africa (1).

Table 1. Shows cases of human influenza A(H9N2) reported to WHO from China from November 12th, 2022 to January 5th, 2023.​
​Date of infection
​County ​

​Disease status
​Source of infection
​Oct. 19th, 2022
​live poultry market
​Oct. 23rd, 2022
​Nov. 13th, 2022​
​live p​oultry market

   3. avian influenza viruses A(H3N8)
On March 27th, 2023, the National Health Commission of the People's Republic of China notified WHO of one confirmed case of human infection with avian influenza A (H3N8) virus. The patient was a 56-year-old woman from Guangdong Province who developed symptoms on February 22nd, 2023. She was admitted to hospital with severe pneumonia on March 3, 2023, and subsequently died on March 16th, 2023.
The patient had a history of exposure to live poultry prior to the onset of the disease, and there are wild birds around her home. The close contacts of the case did not show any infection or symptoms at the time of reporting.
Environmental samples were collected from the patient's place of residence and the market. Test results showed that samples collected from the market tested positive for influenza A (H3) virus (4).

Swine influenza viruses
  1.  influenza viruses A (H1) v
Since the last risk assessment on November 11, 2022, a human case of influenza A(H1) virus was detected on December 5, 2022. This is the first human case of influenza A(H1N2) v reported in Taiwan, China in 2022, and the second since 2021. The case is a 7-year-old girl who lives with her family who owns a pig pen in Changhua County, and had no direct exposure to pigs. She developed an influenza-like illness on September 24, 2022. She visited the emergency department on September 26, had a respiratory sample collected, and tested positive for influenza A on a rapid influenza test. The virus was identified as influenza A (H1N2) v on October 11 after the sample was sent to the Centers for Disease Control and Prevention. Then all family members were tested and results were negative (1).
The genetic sequence of the virus from this case differs from the previous case reported in March 2021, and a thorough epidemiological investigation has ruled out any possible link between the two human cases. Samples from pigs in the family barn were also tested by PCR and tested negative for influenza (1).

Risk assessment:
  • Most human cases have occurred after exposure to infected animals or contaminated environments. Reported human infections tend to be of mild clinical disease. More human infections can be expected as the virus continues to be detected in poultry flocks and swine populations.
  • Current epidemiological and virological evidence indicates that influenza A(H5), A(H9N2), A(H1)v and A(H3N8) influenza viruses have not acquired the ability to sustain human-to-human transmission, and thus the potential for human-to-human transmission is low.
  •  If infected individuals travel from affected areas internationally, their infection may be detected in another country during travel or after arrival. If this happens, further community spread is considered unlikely because these viruses have not acquired the ability to transmit easily between humans (1), (4).
General recommendations for risk management:
  • WHO does not recommend special screening of travelers at points of entry or restrictions regarding the current status of influenza viruses at the human-animal interface.
  • If traveling to countries where animal influenza is known to occur, avoid farms, contact with animals in live animal markets, enter areas where animals may be slaughtered, or touch any surface contaminated with animal waste. It is also recommended to wash their hands often with soap and water. All personnel must also follow good food safety and hygiene practices.
  • Given the extent and frequency of avian influenza cases observed in wild birds, WHO advises the public to avoid contact with sick or dead birds, including wild birds, and to report dead wild birds or request their removal by contacting local wildlife or veterinary authorities.
  • Global surveillance to detect virological, epidemiological and clinical changes associated with the spread of influenza viruses that may affect human and animal health. and cooperation between the animal and human health sectors. And systematic follow-up of suspected human cases.
  • In the current COVID-19 pandemic, vigilance should be maintained for the emergence of new influenza viruses that may be pandemic potential.
  • All laboratory-confirmed human infections caused by a new subtype of influenza virus must be reported under the International Health Regulations (IHR, 2005)(1).
  • The diversity of zoonotic influenza viruses requires increased surveillance in both animals and humans, as well as comprehensive screening of all zoonotic infections and planning for epidemics. To prevent a viral mutation that could make human-to-human transmission easier, the World Health Organization recommends that poultry workers receive seasonal influenza vaccination (4).

Last Update : 26 April 2023 10:30 AM
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