Hendra virus infection: Rare emerging zoonosis causing severe disease in horses and humans
Hendra virus infection: Rare deadly zoonosis transmitted from bats to horses to humans
Veterinarian Dr. Lisa Thompson (Brisbane, Australia) remembers the terror of September 1994. Two racehorses in the suburb of Hendra developed severe respiratory illness. Within days, 19 more horses fell sick. They gasped for breath, foam pouring from nostrils, bodies burning with fever. Fourteen died despite aggressive treatment.
Then horse trainer Vic Rail became ill. High fever, headaches, drowsiness. Days later he fell into a coma and died. Stable hand Ray Unwin developed similar symptoms but survived after weeks in intensive care.
“We’d never seen anything like it,” Dr. Thompson recalled, voice still shaken three decades later. “Horses dying in agony, then humans falling sick with the same mysterious illness. We had no idea what we were dealing with—a completely unknown virus jumping from animals to people.”
Laboratory analysis revealed a terrifying new pathogen: Hendra virus, named after the Brisbane suburb where it first emerged. Scientists traced its origin to fruit bats roosting in trees near the stables. Bats shed the virus in urine and saliva. Horses ate contaminated food. Humans caring for sick horses caught the virus through close contact.
“That outbreak changed Australian veterinary medicine forever,” Dr. Thompson explained. “We realized we faced a deadly emerging disease capable of wiping out horses and killing the people who care for them.”
According to WHO, Hendra virus (HeV) infection is a rare emerging zoonosis (disease that can be transmitted to humans from animals) that causes severe and often fatal disease in both infected horses and humans. The natural host of the virus has been identified as being fruit bats of the Pteropodidae Family, Pteropus genus.
For more on zoonotic diseases, see our articles on emerging infectious diseases and animal-to-human disease transmission at ObserverVoice.com. Related topics include Nipah virus infection, a closely related deadly zoonotic virus. WHO provides fact sheet on Nipah virus.
Discovery and Outbreak History
Hendra virus was identified during the first recorded outbreak of the disease in the Brisbane suburb of Hendra, Australia, in 1994. The outbreak involved 21 stabled racehorses and two human cases. As of July 2016, 53 disease incidents involving over 70 horses have been reported. These incidents were all confined to the north-eastern coast of Australia.
A total of seven humans have contracted Hendra virus from infected horses, particularly through close contact during care or necropsy of ill or dead horses. The geographic restriction to north-eastern Australia reflects the natural range of fruit bat populations carrying the virus. WHO provides Hendra virus outbreaks map showing all documented incidents.
The transmission pathway is clear but frightening: fruit bats (flying foxes) serve as natural reservoir hosts, carrying Hendra virus without becoming ill. These bats feed on fruit and nectar, roosting in trees near horse pastures and stables. They shed virus through urine, saliva, and birth fluids. Horses become infected by consuming food or water contaminated by bat secretions. Humans then contract the disease through close contact with infected horses—particularly veterinarians, stable workers, and horse owners caring for sick animals or performing necropsies on dead horses.
For more on disease transmission pathways, see our article on zoonotic disease prevention at ObserverVoice.com.
Severe Clinical Symptoms
Symptoms of Hendra virus infection in humans range from mild influenza-like illness to fatal respiratory or neurological disease. The variability in severity makes Hendra virus particularly dangerous—some patients develop only mild symptoms while others progress rapidly to life-threatening respiratory failure or encephalitis.
Early symptoms typically include fever, cough, sore throat, headache, and fatigue—easily mistaken for common flu. However, in severe cases, patients develop acute respiratory distress syndrome with difficulty breathing, pneumonia, and respiratory failure requiring mechanical ventilation. Neurological symptoms include confusion, seizures, and coma. The fatality rate in confirmed human cases is extraordinarily high—four of seven documented human infections resulted in death, representing a 57% case fatality rate.
Horses infected with Hendra virus typically develop severe respiratory illness with rapid onset, high fever, increased heart rate, frothy nasal discharge, difficulty breathing, and neurological signs including stumbling and inability to stand. Most infected horses die within days despite aggressive veterinary treatment.
Limited Treatment Options
There is no specific treatment for human cases of Hendra virus. Intensive supportive care is provided, and the use of monoclonal antibodies is being investigated. Patients require intensive care unit management with mechanical ventilation for respiratory support, IV fluids for hydration, medications to support blood pressure and organ function, and treatment of secondary infections.
The lack of specific antiviral treatment makes prevention absolutely critical. A registered Hendra animal vaccine exists and vaccination is recognised as an effective way to reduce the risk of horses becoming infected and to reduce the likelihood of human exposure. Since the vaccine’s introduction in 2012, vaccinated horses have shown excellent protection against Hendra virus infection.
The equine vaccine represents a “One Health” approach—protecting animal health to prevent human disease. Widespread horse vaccination in high-risk areas of Australia has dramatically reduced Hendra virus spillover events. Veterinary authorities strongly recommend vaccination for all horses in endemic areas, particularly those in contact with flying fox habitats.
WHO’s Response and Resources
WHO coordinates global surveillance and research on emerging zoonotic diseases including Hendra virus infection. WHO’s Emergencies Programme provides technical support for outbreak investigation, laboratory diagnosis, infection control, and clinical management.
WHO published Guidance on regulations for the transport of infectious substances 2019-2020 providing protocols for safely handling Hendra virus samples. WHO published Communication for behavioural impact (COMBI) – field workbook supporting implementation of outbreak prevention and control measures. WHO published Communication for behavioural impact (COMBI) – toolkit useful for designing effective outbreak prevention in community settings.
WHO maintains Latest outbreak news providing Disease Outbreak News updates on emerging infections globally. WHO published Nipah virus WER No 9, 2004 documenting related henipavirus outbreaks.
Dr. Thompson now trains veterinarians worldwide on zoonotic disease safety. “Hendra virus taught us that emerging diseases don’t announce themselves with warning signs. They appear suddenly, kill rapidly, and require immediate coordinated response. Every veterinarian, stable worker, and horse owner in endemic areas must understand the risks.”
“The good news is we now have tools to protect ourselves,” Dr. Thompson continued. “Horse vaccination works extraordinarily well. Simple biosecurity measures—wearing protective equipment when handling sick horses, avoiding contact with bat roosts, maintaining hygiene—prevent transmission. Knowledge saves lives. Since widespread vaccine adoption and improved safety protocols, human cases have become extremely rare. We can coexist safely with fruit bats and horses if we respect the risks and take appropriate precautions.”
For more information, visit WHO’s Hendra virus infection topic page or explore related content at ObserverVoice.com.
Frequently Asked Questions (FAQs)
Hendra virus (HeV) infection is rare emerging zoonosis (disease that can be transmitted to humans from animals) that causes severe and often fatal disease in both infected horses and humans. Natural host of virus has been identified as being fruit bats of Pteropodidae Family, Pteropus genus. Hendra virus was identified during first recorded outbreak of disease in Brisbane suburb of Hendra, Australia, in 1994. Outbreak involved 21 stabled racehorses and two human cases. As of July 2016, 53 disease incidents involving over 70 horses have been reported. These incidents were all confined to north-eastern coast of Australia. Total of seven humans have contracted Hendra virus from infected horses, particularly through close contact during care or necropsy of ill or dead horses. Transmission pathway: fruit bats shed virus through urine, saliva, birth fluids; horses consume contaminated food/water; humans contract disease through close contact with infected horses. Related: Nipah virus infection. WHO provides Hendra virus outbreaks map.
Symptoms of Hendra virus infection in humans range from mild influenza-like illness to fatal respiratory or neurological disease. Early symptoms typically include fever, cough, sore throat, headache, and fatigue. In severe cases, patients develop acute respiratory distress syndrome with difficulty breathing, pneumonia, and respiratory failure requiring mechanical ventilation. Neurological symptoms include confusion, seizures, and coma. Fatality rate in confirmed human cases is extraordinarily high—four of seven documented human infections resulted in death, representing 57% case fatality rate. Horses infected with Hendra virus typically develop severe respiratory illness with rapid onset, high fever, increased heart rate, frothy nasal discharge, difficulty breathing, and neurological signs. Most infected horses die within days despite aggressive veterinary treatment. WHO provides fact sheet on Nipah virus, closely related henipavirus.
There is no specific treatment for human cases of Hendra virus. Intensive supportive care is provided, and use of monoclonal antibodies is being investigated. Patients require intensive care unit management with mechanical ventilation for respiratory support, IV fluids for hydration, medications to support blood pressure and organ function, and treatment of secondary infections. Lack of specific antiviral treatment makes prevention absolutely critical. A registered Hendra animal vaccine exists and vaccination is recognised as effective way to reduce risk of horses becoming infected and to reduce likelihood of human exposure. Since vaccine’s introduction in 2012, vaccinated horses have shown excellent protection against Hendra virus infection. Equine vaccine represents “One Health” approach—protecting animal health to prevent human disease. Widespread horse vaccination in high-risk areas of Australia has dramatically reduced Hendra virus spillover events. Veterinary authorities strongly recommend vaccination for all horses in endemic areas.
Hendra virus was identified during first recorded outbreak in Brisbane suburb of Hendra, Australia, in 1994. Outbreak involved 21 stabled racehorses and two human cases. As of July 2016, 53 disease incidents involving over 70 horses have been reported. These incidents were all confined to north-eastern coast of Australia. Geographic restriction to north-eastern Australia reflects natural range of fruit bat populations carrying virus. Natural host of virus has been identified as being fruit bats of Pteropodidae Family, Pteropus genus. These bats feed on fruit and nectar, roosting in trees near horse pastures and stables. They shed virus through urine, saliva, and birth fluids. Horses become infected by consuming food or water contaminated by bat secretions. Total of seven humans have contracted Hendra virus from infected horses, particularly through close contact during care or necropsy of ill or dead horses. WHO provides Hendra virus outbreaks map showing all documented incidents.
WHO published Guidance on regulations for transport of infectious substances 2019-2020 providing protocols for safely handling Hendra virus samples. WHO published Communication for behavioural impact (COMBI) – field workbook supporting implementation of outbreak prevention and control measures in community settings. WHO published Communication for behavioural impact (COMBI) – toolkit useful for designing effective outbreak prevention. WHO published Nipah virus WER No 9, 2004 documenting related henipavirus outbreaks. WHO maintains Latest outbreak news providing Disease Outbreak News updates on emerging infections globally. WHO’s Emergencies Programme provides technical support for outbreak investigation, laboratory diagnosis, infection control, and clinical management. WHO provides fact sheet on Nipah virus, closely related zoonotic virus.
- WHO Hendra Virus Infection Topic Page
- WHO Fact Sheet on Nipah Virus (Related Henipavirus)
- Hendra Virus Outbreaks Map
- WHO Guidance on Transport of Infectious Substances
- WHO Disease Outbreak News
Disclaimer: This article is an adaptation of publicly available information from WHO’s Hendra virus infection 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
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