Hendra virus (HeV) is a rare but severe zoonotic disease, meaning it can naturally transmit from animals to humans. The virus was first identified in 1994 during an outbreak in Hendra, Brisbane, Australia. HeV is classified in the genus Henipavirus, belonging to the Paramyxoviridae family, which it shares with the closely related Nipah virus. This pathogen causes a highly fatal illness in both horses and people.
The Virus’s Natural Host and Transmission Pathways
The natural reservoir for Hendra virus is the flying fox, a type of fruit bat belonging to the genus Pteropus that is native to Australia. These bats carry the virus without developing symptoms and are responsible for maintaining HeV in the wild. Flying foxes shed the virus into the environment primarily through their urine, feces, and birthing products, which can contaminate feed, water, or grazing areas.
Horses act as the intermediate host for the virus, contracting the infection from this environmental contamination. This typically occurs when horses graze beneath trees where flying foxes have been feeding or roosting. Once a horse is infected, the virus replicates to high levels, transforming the animal into the direct source of nearly all documented human infections.
Human exposure occurs when an individual has close contact with the body fluids, tissues, or excretions of an infected horse. High-risk exposures often involve performing invasive procedures, such as veterinary examinations or necropsies, without appropriate personal protective equipment.
Clinical Manifestations and Human Impact
Hendra virus infection in humans is characterized by a high case fatality rate, with four of the seven confirmed cases resulting in death. Following an incubation period that typically ranges from nine to sixteen days, the illness can manifest in one of two main clinical forms. The first is an acute respiratory syndrome, which presents with severe flu-like symptoms, including fever, headache, and respiratory distress resembling pneumonia.
The second manifestation is a neurological disease known as encephalitis, or inflammation of the brain. Patients may initially experience non-specific symptoms like myalgia (muscle pain), sore throat, and cough before the rapid onset of neurological signs. These severe symptoms include drowsiness, disorientation, vertigo, and a lack of coordination.
The neurological form can progress quickly and may result in death or long-term complications for survivors. In some rare instances, a person who initially recovers from the virus may experience a fatal relapse of encephalitis months or years later.
Critical Prevention and Biosecurity Measures
Prevention efforts focus primarily on breaking the transmission chain at the most vulnerable point: the horse. The single most effective measure for managing the risk of HeV infection is the vaccination of horses. A registered vaccine, Equivac HeV, is available and recommended for all horses in endemic areas, as it prevents the horse from developing the disease and shedding the virus.
Horse owners and veterinary professionals must implement strict biosecurity protocols, especially when dealing with a sick horse. Any horse showing sudden illness, fever, or neurological signs should be immediately isolated from other animals and people. Furthermore, feed and water sources should be protected from potential contamination by flying fox excretions, for example, by removing them from under trees.
Veterinary staff attending to suspected HeV cases must use extensive personal protective equipment (PPE), including gloves, gowns, and respiratory protection, to prevent high-level exposure to the horse’s bodily fluids. While there is no commercially available vaccine for humans, treatment for exposed individuals involves intensive supportive care. Monoclonal antibody therapy is also a treatment option being investigated and used for post-exposure management.