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Today's update describes a case with pre-existing respiratory conditions, hospitalized in early March, although H9N2 wasn't identified until late April. It isn't clear why this case wasn't reported to the WHO until May 22nd.
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This afternoon the WHO has published a DON report on a human infection with LPAI H9N2 - India's second (see 2019 report) - which resulted in a prolonged hospitalization, and intubation, of a 4-year old boy in West Bengal.
Roughly 130 cases have been reported (see FluTracker's list) over the past 25 years - and while most have been mild - a few hospitalizations and at least two deaths have been reported. Nearly 90% of all known cases have been reported by China.
As an LPAI (low path avian influenza), H9N2 is not considered a `reportable' disease by WOAH (formerly the OIE), even though it is zoonotic. We've seen seroprevalence studies showing people with exposure to infected poultry often develop H9 antibodies, suggesting mild or asymptomatic infection.
H9N2 infection is likely more common than we know, since the virus is widespread across Asia, and has made inroads into the Middle East and Sub-Saharan Africa; all regions where testing and surveillance are likely to be sub-optimal.
While admittedly not at the very top of our list of pandemic concerns, the CDC has 2 different lineages (A(H9N2) G1 and A(H9N2) Y280) on their short list of influenza viruses with zoonotic potential (see CDC IRAT SCORE), and several candidate vaccines have been developed.
But H9N2's biggest threat may come from its unique ability to reassort with other, potentially more dangerous, avian viruses. Its internal genes have often been found inside many HPAI viruses (including H5N1, H5N6, H7N9, and most recently zoonotic H3N8) - (see The Lancet's Poultry carrying H9N2 act as incubators for novel human avian influenza viruses).
Today's update describes a case with pre-existing respiratory conditions, hospitalized in early March, although H9N2 wasn't identified until late April. It isn't clear why this case wasn't reported to the WHO until May 22nd.
The WHO continues to reminds its members:
All human infections caused by a new subtype of influenza virus are notifiable under the IHR (2005). State Parties to the IHR (2005) are required to immediately notify WHO of any laboratory-confirmed case of a recent human infection caused by an influenza A virus of pandemic potential (IVPP).
Excerpts from today's report follow:
Avian Influenza A (H9N2) - India
11 June 2024
Situation at a glance
On 22 May 2024, the International Health Regulations (IHR) National Focal Point (NFP) for India reported to WHO a case of human infection with avian influenza A(H9N2) virus detected in a child resident of West Bengal state in India. This is the second human infection of avian influenza A(H9N2) notified to WHO from India, with the first in 2019. The child has recovered and was discharged from hospital.
According to the IHR (2005), a human infection caused by a novel influenza A virus subtype is an event that has the potential for high public health impact and must be notified to the WHO. Most human cases of infection with avian influenza A(H9N2) viruses are exposed to the virus through contact with infected poultry or contaminated environments. Human infection tends to result in mild clinical illness.
Based on available information, further sporadic human cases could occur as this virus is one of the most prevalent avian influenza viruses circulating in poultry in different regions. With the currently available evidence, WHO assesses the current public health risk to the general population posed by this virus as low. However, the risk assessment will be reviewed should further epidemiological or virological information become available.
Description of the situation
On 22 May 2024, WHO received a notification from the IHR NFP regarding a human case of avian influenza A(H9N2) virus infection in West Bengal state, India.
The patient is a 4-year-old child residing in West Bengal state. The case, previously diagnosed with hyperreactive airway disease, initially presented to the paediatrician with fever and abdominal pain on 26 January 2024. On 29 January, the patient developed seizures and was brought to the same paediatrician. On 1 February, the patient was admitted to the pediatric intensive care unit (ICU) of a local hospital due to the persistence of severe respiratory distress, recurrent high-grade fever and abdominal cramps. The patient was diagnosed with post-infectious bronchiolitis caused by viral pneumonia. On 2 February, the patient tested positive for influenza B and adenovirus at the Virus Research and Diagnostic Laboratory at the local government hospital. The patient was discharged from the hospital on 28 February 2024.
On 3 March, with a recurrence of severe respiratory distress, he was referred to another government hospital and was admitted to the pediatric ICU and intubated. On 5 March, a nasopharyngeal swab was sent to the Kolkata Virus Research and Diagnostic Laboratory and tested positive for influenza A (not sub-typed) and rhinovirus. The same sample was sent to the National Influenza Centre at the National Institute of Virology in Pune for subtyping. On 26 April, the sample was sub-typed as influenza A(H9N2) through a real-time polymerase chain reaction. On 1 May, the patient was discharged from the hospital with oxygen support. Information on the vaccination status and details of antiviral treatment were not available at the time of reporting.
The patient had exposure to poultry at home and in the surroundings. There were no known persons reporting symptoms of respiratory illness in the family, the neighbourhood, or among healthcare workers at health facilities attended by the case at the time of reporting.
This is the second human infection of avian influenza A(H9N2) virus infection notified to WHO from India, with the first in 2019. Further sporadic human cases could occur as this virus is one of the most prevalent avian influenza viruses circulating in poultry in different regions.
(SNIP)
WHO risk assessment
Most human cases of infection with avian influenza A(H9N2) viruses are exposed to the virus through contact with infected poultry or contaminated environments. Human infection tends to result in mild clinical illness. However, globally, there have been some hospitalized cases and two fatal cases reported in the past. Given the continued detection of the virus in poultry populations, sporadic human cases can be expected.
No additional confirmed cases have been reported in the local area based on joint investigations.Currently, available epidemiological and virological evidence suggests that this virus has not acquired the ability to be sustained in transmission among humans. Thus, the likelihood of human-to-human spread is low. However, the risk assessment will be reviewed should further epidemiological or virological information become available.International travellers from affected regions may present with infections either during their travels or after arrival in other countries. Even if this were to occur, further community-level spread is considered unlikely as this virus has not acquired the ability to transmit easily among humans.
Currently, available epidemiological and virological evidence suggests that this virus has not acquired the ability to be sustained in transmission among humans. Thus, the likelihood of human-to-human spread is low. However, the risk assessment will be reviewed should further epidemiological or virological information become available.
International travellers from affected regions may present with infections either during their travels or after arrival in other countries. Even if this were to occur, further community-level spread is considered unlikely as this virus has not acquired the ability to transmit easily among humans.
