Influenza (avian and other zoonotic): Animal influenza viruses infecting humans
Avian and zoonotic influenza: Animal flu viruses jumping to humans
Nguyen Van Hai (Vietnam) never imagined that caring for his chickens would nearly kill him. A small-scale poultry farmer in the Mekong Delta, he’d raised chickens his entire life—just like his father and grandfather before him. In January 2004, several of his birds began dying mysteriously. High fever, respiratory distress, sudden death. Within days, his entire flock of 200 chickens was dead.
“I handled the sick birds, tried to save them, cleaned out the coops after they died. I didn’t wear gloves or a mask—I’d been handling chickens for 30 years without problems. Why would I need protection now?” Nguyen recalled from his hospital bed, struggling to breathe through an oxygen mask.
Three days after his last chicken died, Nguyen developed symptoms. High fever, severe cough, difficulty breathing. His wife took him to the local clinic. The doctor initially diagnosed pneumonia and prescribed antibiotics. But Nguyen’s condition deteriorated rapidly. Within 48 hours, he was fighting for his life in the provincial hospital’s intensive care unit, connected to a ventilator.
“The doctors told my wife I had avian influenza—bird flu—H5N1 virus. They said my survival was uncertain. Many patients with H5N1 die—over half of reported cases. I was 42 years old, previously healthy, but this virus was destroying my lungs. My wife was terrified. Our five children—ages 6 to 16—might lose their father. All because I handled sick chickens without protection.”
According to WHO, animal influenza viruses are distinct from human seasonal influenza viruses and do not easily transmit between humans. However, zoonotic influenza viruses – animal influenza viruses that may occasionally infect humans through direct or indirect contact – can cause disease in humans ranging from a mild flu-like illness or eye inflammation to severe acute respiratory disease and, in some cases, death.
For more on infectious diseases, see our articles on pandemic preparedness and emerging diseases at ObserverVoice.com.
Avian, Swine and Other Animal Influenza
Birds are the natural hosts for avian influenza viruses. After an outbreak of A(H5N1) virus in 1997 in poultry in Hong Kong SAR, China, since 2003, this avian and other influenza viruses have spread from Asia to Europe and Africa. In 2013, human infections with the influenza A(H7N9) virus were reported in China. In 2024, A(H5N1) viruses spread to dairy cattle in the United States of America and caused outbreaks. Some dairy farm workers who had direct contact with the infected cows were also infected.
Most swine influenza viruses do not cause disease in humans, but some countries have reported cases of human infection from certain swine influenza viruses. Close proximity to infected pigs or visiting locations where pigs are exhibited has been reported for most human cases, but some limited human-to-human transmission has occurred. Just like birds and pigs, other animals such as horses and dogs, can be infected with their own influenza viruses (canine influenza viruses, equine influenza viruses, etc.).
Human infections with avian influenza viruses can cause illness ranging from mild, flu-like symptoms or eye inflammation (conjunctivitis) to severe, acute respiratory disease and death. Gastrointestinal and neurological symptoms have been reported infrequently. Disease severity depends upon many factors, including the virus causing the infection, the nature of exposure, clinical management, laboratory testing, and the characteristics of the infected individual. The reported case fatality rate for human infection with A(H5) and A(H7N9) viruses to date has been higher than that of seasonal influenza.
WHO provides Influenza (avian and other zoonotic) fact sheet, Frequently asked questions on avian influenza, and Frequently asked questions on H5N1 influenza.
Related topics include Influenza (seasonal). For more on disease surveillance, see our article on global health monitoring at ObserverVoice.com.
Treatment and WHO Response
If a person is suspected of having zoonotic influenza, the health authorities should be notified and appropriate clinical management should be provided, including testing, triage, clinical assessment for disease severity classification, assessment of risk factors for severe disease, and isolation and treatment (for example, with antivirals and supportive care). Patients with influenza should be managed properly to prevent severe illness and death.
Human infections with swine influenza viruses have generally been mild, with symptoms similar to those of human seasonal influenza – although in some cases, the patients needed hospitalization. The classification of low or high pathogenicity of avian influenza viruses (LPAI or HPAI) relates to disease presentation in chickens and is not related to disease in humans.
WHO’s Global Influenza Programme (GIP) coordinates global efforts. WHO established Global Influenza Surveillance and Response System (GISRS) for surveillance. WHO implements Pandemic Influenza Preparedness Framework (PIP) for preparedness. WHO provides Global influenza virological surveillance database and GHO Map gallery on avian influenza.
World Health Assembly passed WHA64.5 on Pandemic influenza preparedness: sharing of influenza viruses and access to vaccines and other benefits.
Recent Publications and Surveillance
September 2025 WHO published Public health resource pack for countries experiencing outbreaks of influenza in animals: revised guidance as overview for country offices. August 2025 WHO published Pandemic influenza severity assessment (PISA): a WHO guide to assess severity, second edition providing systematic approach. June 2025 WHO published Considerations for use of avian influenza A(H5) vaccines during interpandemic and emergence periods providing overview of vaccine landscape. April 2025 WHO published Surveillance for human infections with avian influenza A(H5) viruses: objectives, case definitions, testing and reporting for detection and characterization.
March 2025 WHO reported Despite global influenza vaccine production remaining steady, production and distribution challenges remain. March 2025 WHO reported Influenza surveillance in conflict-affected areas of Myanmar. March 2025 WHO reported Enhancing respiratory syncytial virus (RSV) surveillance in Mongolia. October 2024 WHO reported Pioneering regional collaboration to enhance regulatory practices in the Americas.
December 2025 WHO featured Republic of Congo strengthens regional pandemic preparedness with influenza sentinel surveillance system. December 2025 WHO featured Strengthening Ukraine’s pandemic preparedness: One Health approach. December 2025 WHO featured South-East Asia Region on course for stronger pandemic preparedness. December 2025 WHO featured Uzbekistan’s virology laboratory achieves ISO accreditation.
WHO partners with World Organisation for Animal Health (OIE), Food and Agriculture Organization (FAO), Global early warning system (GLEWS), and OIE/FAO Network of Expertise on Animal Influenza (OFFLU).
Recovery and Prevention Through Awareness
Nguyen survived his H5N1 infection—one of the fortunate ones. After three weeks in intensive care and two months of recovery, he returned home. But he returned changed—not just physically weakened, but transformed in his understanding of disease prevention and biosecurity.
“I learned that avian influenza is deadly serious—not just another chicken disease. I learned that viruses don’t respect the boundaries between animals and humans. I learned that simple protective measures—wearing gloves, masks, disposing of dead birds properly, reporting sick flocks immediately—can save lives. I survived, but many others in Vietnam died from H5N1. They were farmers like me who didn’t understand the risks,” Nguyen explained.
“After my recovery, I became a community health educator working with WHO-supported programs. I teach poultry farmers about biosecurity—how to protect themselves and their birds. I explain that unusual bird deaths should be reported immediately to veterinary authorities. I demonstrate proper protective equipment. I emphasize that cooking poultry thoroughly kills flu viruses—raw or undercooked poultry is dangerous. I share my story to show that bird flu is real, deadly, and preventable,” Nguyen continued.
“WHO’s Global Influenza Surveillance and Response System monitors animal and human influenza viruses globally. When outbreaks occur in animals, WHO works with countries to implement control measures, protect people at risk, and prepare for potential pandemics. The Pandemic Influenza Preparedness Framework ensures countries can access vaccines and medical countermeasures if animal flu viruses develop pandemic potential,” Nguyen emphasized.
“H5N1 killed over half of people infected in early outbreaks. That case fatality rate is terrifying—far higher than seasonal flu. In 2024, H5N1 spread to dairy cattle in the United States—showing these viruses continue evolving, jumping to new species. Every animal-to-human transmission is a warning. Every outbreak in animals is a pandemic risk. WHO’s surveillance, research, and preparedness efforts are essential to preventing the next influenza pandemic. My survival reminds me daily: zoonotic influenza isn’t theoretical—it’s killing people now and threatens billions more if pandemic strains emerge. WHO’s leadership is our best defense against that catastrophic possibility.”
For more information, visit WHO’s influenza (avian and other zoonotic) topic page or explore related content at ObserverVoice.com.
Frequently Asked Questions (FAQs)
Animal influenza viruses are distinct from human seasonal influenza viruses and do not easily transmit between humans. However, zoonotic influenza viruses – animal influenza viruses that may occasionally infect humans through direct or indirect contact – can cause disease in humans ranging from mild flu-like illness or eye inflammation to severe acute respiratory disease and death. Birds are natural hosts for avian influenza viruses. After outbreak of A(H5N1) virus in 1997 in poultry in Hong Kong SAR, China, since 2003, this avian and other influenza viruses have spread from Asia to Europe and Africa. In 2013, human infections with influenza A(H7N9) virus were reported in China. In 2024, A(H5N1) viruses spread to dairy cattle in United States and caused outbreaks. Most swine influenza viruses do not cause disease in humans, but some countries have reported cases of human infection. Just like birds and pigs, other animals such as horses and dogs can be infected with their own influenza viruses. WHO provides Influenza fact sheet and FAQs on avian influenza. Related: Influenza (seasonal).
Human infections with avian influenza viruses can cause illness ranging from mild, flu-like symptoms or eye inflammation (conjunctivitis) to severe, acute respiratory disease and death. Gastrointestinal and neurological symptoms have been reported infrequently. Disease severity depends upon many factors, including virus causing infection, nature of exposure, clinical management, laboratory testing, and characteristics of infected individual. Reported case fatality rate for human infection with A(H5) and A(H7N9) viruses to date has been higher than that of seasonal influenza. Classification of low or high pathogenicity of avian influenza viruses (LPAI or HPAI) relates to disease presentation in chickens and is not related to disease in humans. Human infections with swine influenza viruses have generally been mild, with symptoms similar to those of human seasonal influenza – although in some cases, patients needed hospitalization. WHO provides FAQs on H5N1 influenza. September 2025 WHO published Public health resource pack for countries experiencing outbreaks. August 2025 WHO published Pandemic influenza severity assessment guide. Related: Influenza (seasonal).
If person is suspected of having zoonotic influenza, health authorities should be notified and appropriate clinical management should be provided, including testing, triage, clinical assessment for disease severity classification, assessment of risk factors for severe disease, and isolation and treatment (for example, with antivirals and supportive care). Patients with influenza should be managed properly to prevent severe illness and death. Close proximity to infected animals or visiting locations where animals are exhibited has been reported for most human cases. June 2025 WHO published Considerations for use of avian influenza A(H5) vaccines providing overview. April 2025 WHO published Surveillance for human infections with avian influenza A(H5) viruses. March 2025 WHO reported Global influenza vaccine production challenges. WHO’s Global Influenza Programme coordinates efforts. Related: Influenza (seasonal).
WHO’s Global Influenza Programme (GIP) coordinates global efforts. WHO established Global Influenza Surveillance and Response System (GISRS) for surveillance. WHO implements Pandemic Influenza Preparedness Framework (PIP) for preparedness. WHO provides Global influenza virological surveillance database and GHO Map gallery on avian influenza. World Health Assembly passed WHA64.5 on Pandemic influenza preparedness. December 2025 WHO featured Congo strengthens pandemic preparedness with surveillance. December 2025 WHO featured Ukraine’s One Health approach. December 2025 WHO featured South-East Asia Region preparedness. March 2025 WHO reported Influenza surveillance in Myanmar. Related: Influenza (seasonal).
WHO partners with World Organisation for Animal Health (OIE), Food and Agriculture Organization (FAO), Global early warning system for major animal diseases including zoonoses (GLEWS), and OIE/FAO Network of Expertise on Animal Influenza (OFFLU) to coordinate surveillance of animal influenza viruses. September 2025 WHO published Public health resource pack for outbreaks in animals. October 2024 WHO reported Pioneering regional collaboration in the Americas. December 2025 WHO featured Uzbekistan’s laboratory achieves ISO accreditation. March 2025 WHO reported Enhancing RSV surveillance in Mongolia. WHO’s Global Influenza Programme coordinates implementation. WHO provides FAQs on avian influenza and FAQs on H5N1. Related: Influenza (seasonal).
- WHO Influenza (Avian and Other Zoonotic) Topic Page
- WHO Global Influenza Surveillance and Response System
- WHO Pandemic Influenza Preparedness Framework
- WHO Global Influenza Programme
- OIE/FAO Network on Animal Influenza (OFFLU)
Disclaimer: This article is an adaptation of publicly available information from WHO’s Influenza (avian and other zoonotic) health topic page (WHO, Geneva. Licence: CC BYNC-SA 3.0 IGO). WHO is not responsible for the content or accuracy of this adaptation. This content is for informational and educational purposes
only and does not constitute medical advice. ObserverVoice.com is a news and information platform
— not a healthcare provider.
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