Situation at a glance
Between 1 January and 1 July 2025, the World Health Organization (WHO) was notified by Cambodia’s International Health Regulations (IHR) National Focal Point (NFP) of 11 laboratory-confirmed cases of human infection with avian influenza A(H5N1) virus.
Seven of the 11 cases were reported in June, an unusual monthly increase.
Avian influenza A(H5N1) was first detected in Cambodia, in December 2003, initially affecting wild birds.
Since then, 83 cases of human infection with influenza A(H5N1), including 49 deaths (case fatality ratio [CFR] of 59%), have been reported in the country.
While the virus continued to circulate in avian species, no human cases were reported between 2014 and 2022, after which, the virus re-emerged in humans in February 2023.
Since the re-emergence of human A(H5N1) infections in Cambodia in 2023, a total of 27 cases have been reported (six in 2023, 10 in 2024, and 11 to date in 2025), of which 12 were fatal (CFR 44%).
Seventeen of the cases occurred in children under 18 years old.
Avian influenza A(H5N1) is circulating in wild birds, poultry and some mammals around the world, and occasional human infections following exposure to infected animals or contaminated environments are expected to occur.
In cases detected in Cambodia, exposure to sick poultry, often poultry kept in backyards, has been reported.
According to the IHR, 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.
Based on currently available information, WHO assesses the current risk to the general population posed by this virus as low.
For those occupationally exposed to the virus, such as farm workers, the risk is low to moderate, depending on the measures in place.
WHO routinely reassesses this risk to factor in new information.
Description of the situation
Between 1 January and 1 July 2025, the National IHR Focal Point (NFP) of the Kingdom of Cambodia notified WHO of 11 laboratory-confirmed case of human infection with avian influenza A(H5N1) virus (clade 2.3.2.1e- formerly classified as 2.3.2.1c; from cases where virus sequences are available to date) including six deaths [CFR: 54%].
These cases are reported from the provinces of Siem Reap (4), Takeo (2), Kampong Cham (1), Kampong Speu (1), Kratie (1), Prey Veng (1), Svay Rieng (1).
Of the total cases reported in 2025, seven cases were reported in June 2025.
Males account for 63% of the cases. Of the 11 cases, three cases were reported in less than five-year-olds, two cases were between the age of 5 and 18 years and six cases were reported in the age group 18-65 years.
All cases had exposure – handling or culling - of sick poultry, often kept in backyards.
Avian influenza A(H5N1) was detected for the first time in Cambodia in December 2003, initially affecting wild birds. Between 2014 and 2022, there were no reports of human infection with A(H5N1) viruses. However, the re-emergence of human infections with A(H5N1) viruses in Cambodia was reported in February 2023. Since this re-emergence, Cambodia has reported 27 cases of laboratory confirmed human infection with avian influenza A(H5N1) including 12 fatalities (CFR 44%).
The cases have been reported from eight provinces: Kampong Cham (1), Kampong Speu (1), Kampot (3), Kratie (3), Prey Veng (6), Svay Rieng (4), Siem Reap (5), Takeo (4).
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Epidemiology
Animal influenza viruses typically circulate within animal populations, but some have the potential to infect humans. Human infections are predominantly acquired through direct contact with infected animals or exposure to contaminated environments. Based on the original host species, influenza A viruses can be categorized such as avian influenza, swine influenza, and other animal-origin influenza subtypes.
Human infection with avian influenza viruses may result in a spectrum of illness, ranging from mild upper respiratory tract symptoms to severe, life-threatening conditions.
Clinical manifestations include conjunctivitis, respiratory, gastrointestinal symptoms, encephalitis (brain swelling), and encephalopathy (brain damage).
In some cases, asymptomatic infections with the A(H5N1) virus have been reported in individuals with known exposure to infected animals and environments.
A definitive diagnosis of human avian influenza infection requires laboratory confirmation. WHO regularly updates its technical guidance on the detection of zoonotic influenza, utilizing molecular diagnostic methods such as RT-PCR.
Clinical evidence indicates that certain antiviral agents, particularly neuraminidase inhibitors (e.g., oseltamivir, zanamivir), have been shown to shorten the duration of viral replication and improve patient outcomes in some cases. This antiviral agent should be administered within 48 hours of symptom onset.
From 2003 to 1 July 2025, 986 cases of human infections with avian influenza A(H5N1), including 473 deaths (CFR 48%), have been reported to WHO from 25 countries.
Almost all of these cases have been linked to close contact with infected live or dead birds, or contaminated environments.
From 2003 to the present, 83 cases of human infection with influenza A(H5N1), including 49 deaths (case fatality ratio [CFR] of 59%), have been reported in Cambodia.
Public health response
The Ministry of Health's national and sub-national rapid response teams have deployed to conduct further investigations and respond to the outbreak. This is being implemented in coordination with the local authorities, the Ministry of Environment and the Ministry of Agriculture, Forestry, and Fisheries.
Investigations have focussed on identifying the source of transmission in both humans and animals, conducting enhanced surveillance, detecting suspected cases, and preventing community transmission;
-- Close contacts were monitored for their health status;
-- Health education campaigns were conducted for affected villages.
- Animal Health:
-- The investigation and response team from the General Directorate of Animal Health and Production (GDAHP) and the sub-national animal health team conducted outbreak investigation and response to poultry outbreaks, in coordination with Ministry of Health, provincial health departments and local authorities.
-- Investigation on and response to the poultry outbreaks, with the response interventions focusing on disinfection and limiting animal movement across villages;
-- Community awareness and health education to affected communities;
-- Surveillance and monitoring on poultry diseases in affected villages.
WHO risk assessment
From 2003 to 1 July 2025, a total of 986 human cases of infection of influenza A(H5N1) have been reported globally to WHO from 25 countries, including this case. Almost all of these have been linked to close contact with A(H5N1) infected live or dead birds or mammals, or contaminated environments. Human infection can cause severe disease with a high mortality rate: of the 986 infections reported globally, there have been 473 deaths (CFR 48%).
In this event, cases have been reported from seven provinces in 2025. All cases have reported direct exposure to sick/dead poultry. While human-to-human transmission cannot be ruled out, the more likely source of exposure of these cases is infected poultry of contaminated environment.
Based on information available at this time, the overall public health risk from currently known influenza viruses circulating at the human-animal interface has not changed and remains low.
For those occupationally exposed to the virus, such as farm workers, the risk is low to moderate, depending on the measures in place.
Additional cases in persons with exposure to sick/dead poultry is to be expected.
The occurrence of sustained human-to-human transmission in this event based on currently available information is currently considered unlikely.
This can, however, change and the risk assessment will be reviewed as needed if additional information becomes available.
Close analysis of the epidemiological situation, further characterization of the most recent influenza A(H5N1) viruses in both human and animal populations, and serological investigations are critical to update associated risk assessments for public health and promptly adjust risk management measures.
Current seasonal influenza vaccines are unlikely to protect humans against infections with influenza A(H5N1) viruses.
Vaccines against influenza A(H5) infection in humans have been developed and licensed in some countries. WHO continues to update the list of zoonotic influenza candidate vaccine viruses (CVVs), which are selected twice a year at the WHO consultation on influenza virus vaccine composition, and on an ad hoc basis as needed. The list of such CVVs is available on the WHO website, see reference below. In addition, the genetic and antigenic characterization of contemporary animal and zoonotic influenza viruses are published here.
This risk assessment will be reviewed as needed if additional information becomes available.
WHO advice
Based on available information, this event does not change WHO recommendations on public health measures and influenza surveillance.
Given the observed extent and frequency of avian influenza in poultry, wild birds and some wild and domestic mammals, the public should avoid contact with any sick or dead animals.
The public should avoid contact with high-risk environments, such as live animal markets/farms and live poultry or surfaces that might be contaminated by poultry droppings.
Individuals should report deceased birds and mammals or request their removal by contacting local wildlife or veterinary authorities.
Eggs, poultry meat and other poultry products should be properly cooked and handled during food preparation.
Handling sick or dead poultry including slaughtering, butchering, and preparing poultry for consumption, should be avoided.
Additionally, maintaining good hand hygiene through frequent hand washing with soap or using alcohol-based hand sanitizer is recommended.
Any person exposed to potentially infected animal or contaminated environments and feels unwell should seek health care promptly and inform their healthcare provider of their possible exposure.
WHO does not recommend special traveler screening at points of entry or other restrictions due to the current situation of influenza viruses at the human-animal interface.
In the case of a confirmed or suspected human infection caused by a novel influenza A virus with pandemic potential, including avian influenza viruses, a thorough epidemiologic investigation of the history of animal exposure, travel, and contact tracing should be conducted even while awaiting the confirmatory laboratory results.
The epidemiologic investigation should also include early identification of unusual events that could signal person-to-person transmission of the novel virus. Clinical samples collected from confirmed or suspected cases should be tested and sent to a WHO collaborating centre (WHOCC) for further characterization. Additional samples should be collected from animals, the environment or any foods suspected to be sources of infection.
State Parties to the International Health Regulations (2005) are required to immediately notify WHO of any laboratory-confirmed case of a recent human infection caused by a new subtype of influenza virus. Evidence of illness is not required for this notification. WHO has updated the influenza A(H5) confirmed case definition on the WHO website.
Further Informations
-- Ministry of Health Cambodia press release. 1 July 2025: https://moh.gov.kh/kh/notice/detail/183
-- World Health Organization Global influenza programme, human-animal interface: https://www.who.int/teams/global-influenza-programme/avian-influenza
-- World Health Organization Monthly Risk Assessment Summary: Influenza at the human-animal interface: https://www.who.int/teams/global-influenza-programme/avian-influenza/monthly-risk-assessment-summary
-- World Health Organization Avian Influenza Weekly Update: https://www.who.int/westernpacific/emergencies/surveillance/avian-influenza
-- Protocol to investigate non-seasonal influenza and other emerging acute respiratory diseases: https://www.who.int/publications-detail-redirect/WHO-WHE-IHM-GIP-2018.2
-- Surveillance for human infections with avian influenza A(H5) viruses: objectives, case definitions, testing and reporting: https://www.who.int/publications/i/item/B09337
-- Public health resource pack for countries experiencing outbreaks of influenza in animals: revised guidance: https://www.who.int/publications/i/item/9789240076884
-- Implementing the integrated sentinel surveillance of influenza and other respiratory viruses of epidemic and pandemic potential by the Global Influenza Surveillance and Response System: https://www.who.int/publications/i/item/9789240101432
-- Case definitions for the four diseases requiring notification in all circumstances under the International Health Regulations (2005): https://www.who.int/publications/m/item/case-definitions-for-the-four-diseases-requiring-notification-to-who-in-all-circumstances-under-the-ihr-(2005)
-- Evidence-based risk management along the livestock production and market chain: Cambodia: https://www.fao.org/publications/card/en/c/CA7319EN/
-- Disease Outbreak News. 2 September 2024: https://www.who.int/emergencies/disease-outbreak-news/item/2024-DON533
-- Food and Agriculture Organization of the United Nations (FAO). Animal Production and Health Division (NSAH): https://www.fao.org/agriculture/animal-production-and-health/en
-- World Animal Health Organisation (WOAH). World Animal Health Information System (WAHIS). https://wahis.woah.org/#/in-review/5754?reportId=174349&fromPage=event-dashboard-url
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