#19,253
Although reporting has been sporadic, since 2021 China has reported at least 7 human infection with LPAI H10N3. The most recent case (Dec 2025) was announced by Hong Kong last February in an cryptic 1-line notice (see below) in their weekly avian flu report.
In late April the WHO published a brief report where we learned this patient - who worked with poultry - was hospitalized with severe pneumonia, severe acute respiratory distress syndrome (ARDS) and sepsis for roughly 2 weeks before a diagnosis of avian H10 infection was confirmed.
- In July of 2024, in Frontiers: Phylogenetic and Mutational Analysis of H10N3 Avian Influenza A virus in China: Potential Threats to Human Health, we looked at a report that described 4 mutations of concern in the 2023 case (HA Q226L, PB2 D701N, PA S409N, and M2 S31N), along with the patient's treatment and course of illness.
- In December of 2024 Vet. Microbiology: The novel H10N3 Avian Influenza Virus Acquired Airborne Transmission Among Chickens: An Increasing Threat to Public Health reported the virus has become better adapted to poultry, is highly pathogenic in mice, can be transmitted via respiratory droplets between guinea pigs, and can also be transmitted via the airborne route by chickens.
- And last summer, Vet. Research: E627V Mutation in PB2 Protein Promotes the Mammalian Adaptation of Novel H10N3 Avian Influenza Virus reported that that PB2-626V is becoming increasingly common in AIV poultry isolates - including H10N3 - and that it significantly enhances mammalian adaptation while maintaining fitness in avian hosts.
Today we have a detailed case report on the 4th known case - a 23 year-old female who was infected in December of 2024 - and who ended up being hospitalized for > 3 months.
Published: 17 July 2026
Mei Zhao, Qiyun Shi, Lin Zhao, Meng Wang, Jingwen Li, Zhiyi Wan, Tun Ouyang & Yang Yu
Abstract
Background
Human infection with avian influenza A (H10N3) is a rare but severe emerging zoonotic disease. To date, only a limited number of cases have been reported, which restricts a comprehensive understanding of its clinical features and public health risks. We report the fourth documented case of human H10N3 infection, which is the first to be identified in a female patient. Additionally, we compared the clinical and genomic characteristics of all four cases.
Case presentation
A 23-year-old female with no prior comorbidities developed severe pneumonia and acute respiratory distress syndrome due to infection with avian influenza A (H10N3) virus. The patient, working in a fresh market with recent training at a slaughterhouse, presented a one-week history of high fever, cough, and dyspnea. Despite initial broad-spectrum antibiotics, her condition rapidly worsened, requiring mechanical ventilation and veno-venous extracorporeal membrane oxygenation (V-V ECMO). Metagenomic next-generation sequencing of bronchoalveolar lavage fluid, confirmed by the Centers for Disease Control and Prevention, identified avian influenza A (H10N3).
Following approximately three months of intensive treatment, the patient recovered and was discharged. Phylogenetic analyses showed that her virus strain was closest to the third human H10N3 case (Kunming, China, 2024). In addition, this strain had a human-adapted substitution (P221) but lacked the G228S substitution in the haemagglutinin protein, suggesting that the latter is not essential for human infection.
Conclusions
This case highlights the potential for severe human infection by the H10N3 virus. It is imperative that surveillance is enhanced in both human and animal populations.
(SNIP)
A comparative analysis of the four reported human H10N3 infections to date (Table 1) reveals a consistent pattern of severe disease [7,8,9]. All four patients were hospitalized 4–7 days after onset of common respiratory symptoms. The disease generally progresses rapidly, with transfer to the RICU due to ARDS typically occurring 8–10 days after symptom onset (Table 1). Notably, 75% (3/4) of patients required mechanical ventilation or ECMO (Table 1).
These data suggest that H10N3 viruses may induce serious, life-threatening disease in humans.
In addition, this patient received prolonged inpatient treatment for approximately 3 months before discharge, significantly longer than the three previously reported H10N3 cases. The extended hospitalization was primarily attributable to numbness and motor dysfunction of the right lower extremity that developed after successful V-V ECMO weaning.
The patient received inpatient rehabilitation for more than two additional months to achieve full functional recovery before discharge. Similar neurological complications were not documented in the three previously reported human H10N3 cases, which explains the marked difference in the length of hospitalization between this case and prior cases.(SNIP)
In conclusion, we have presented a case of severe pneumonia and ARDS due to avian influenza virus (H10N3) infection in a 23-year-old female. This case highlights the severe pathogenic potential of the H10N3 subtype in humans. This report emphasizes the need for continued surveillance of avian influenza viruses in both animal and human populations.
While the authors call for `continued surveillance', H10N3 (along with H9N2 and a number of other LPAI viruses), are not considered to be a `reportable' disease in poultry by WOAH.
Human cases are reportable to WHO, but - as we've seen - case reports are often vague or sometimes delayed for months. And we've no idea how many cases are missed.
The FAO acknowledges and presents a broad overview of avian flu viruses with zoonotic potential, but no global agency does dedicated tracking of H10N3, H9N2, and similar LPAI viruses in poultry.
Instead we rely on a informal patchwork of sporadic national surveillance, independent research projects, and reports of occasional spillovers into humans (see WHO DON: Avian Influenza A(H9N2) - Italy (Ex Senegal)) to try to monitor these subtypes.
While out attitudes towards these LPAI threats may change over time, hopefully that's not a lesson we'll have to learn the hard way.
