- Hendra virus can cause fatal respiratory and neurological diseases.
- Hendra virus can be transmitted to people from horses.
- Hendra virus can cause severe disease and death in horses.
- There is no treatment or vaccine available for either people or horses.
- Fruit bats of the Pteropodidae family are the natural hosts of Hendra virus.
Hendra virus (HeV) is a rare, emerging zoonotic virus (a virus transmitted to humans from animals), that can cause respiratory and neurological disease and death in people. It can also cause severe disease and death in horses, resulting in considerable economic losses for horse breeders.
Initially named Equine Morbilivirus, Hendra virus is a member of the genus Henipavirus, a new class of virus in the Paramyxoviridae family. It is closely related to Nipah virus.
Although Hendra virus has caused only a few outbreaks, its potential for further spread and ability to cause disease and death in people have made it a public health concern. The concern has heightened in the most recent outbreaks, as the horses’ symptoms have shifted to become largely neurological instead of respiratory. This suggests the possibility of genetic diversity in the strain, and potentially a more infective virus.
Hendra virus was first recognized in 1994 during an outbreak of acute respiratory disease among 21 horses in Australia. Two people were infected, and one died. Since then, there have been another ten outbreaks, all in Australia, and three involving human cases.
Hendra virus is transmitted to people through close contact with infected horses or their body fluids.
To date, no human-to-human transmission of Hendra virus has been documented.
Signs and symptoms
Human infections with Hendra virus range from mild influenza-like illness to fatal respiratory or neurological disease. Infected people initially develop fever, headaches, myalgia (muscle pain), sore throat and a dry cough. They could also have enlarged lymph nodes, lethargy and vertigo.
The incubation period (interval from infection to onset of symptoms) ranges from five to 14 days. To date, there have been six confirmed human cases including three deaths.
One of the people who died developed pneumonitis, respiratory failure, renal failure, and arterial thrombosis. The patient died of cardiac arrest.
Another person demonstrated an unusual, progressive fatal neurological illness. He initially had a mild type of inflammation of the brain (meningoencephalitis) with a sore throat, headache, drowsiness, vomiting and neck stiffness. After treatment with antibiotics, he made a full recovery, but 13 months later he developed signs of encephalitis that progressed to coma and death.
The three infected people who made a full recovery have had no residual problems or relapse.
Hendra virus infection can be diagnosed by a number of different laboratory tests:
- serum neutralization;
- enzyme-linked immunosorbent assay (ELISA);
- polymerase chain reaction (PCR) assay;
- immunofluorescence assay; and
- virus isolation by cell culture.
There are currently no drugs or vaccines available to treat Hendra virus infection. Intensive supportive care with treatment of symptoms is the main approach to managing the infection in people.
Natural host of Hendra virus
Fruit bats of the family Pteropodidae – particularly the species belonging to the Pteropus category – are the natural hosts for Hendra virus. There is no apparent disease in fruit bats.
It is assumed that the geographic distribution of Henipaviruses overlap with that of Pteropus genus. This hypothesis was reinforced with the evidence of Henipavirus infection in Pteropus bats from Australia, Bangladesh, Cambodia, China, India, Indonesia, Madagascar, Malaysia, Papua New Guinea, Thailand and Timor-Leste.
Recently, African fruit bats of the genus Eidolon, family Pteropodidae, were found positive for antibodies against Nipah and Hendra viruses indicating that these viruses might be present within the geographic distribution of Pteropodidae bats in Africa.
Hendra virus in horses
Horses are the only species of domestic animal that can be naturally infected with Hendra virus. Infections in horses range from asymptomatic infection to fatal respiratory and neurological syndromes. For fatal cases, the course of illness takes an average of two days.
Symptoms of Hendra virus infection in horses are not dramatically different from other respiratory and neurological illnesses of horses. Hendra should be suspected if there is also the proximity of bats, or the presence of human cases of acute respiratory distress syndrome or encephalitis. Generally Hendra virus outbreaks in horses occur one to two weeks before illness in humans; detected outbreaks in horses could trigger prevention measures to deter associated outbreaks in humans.
The incubation period (interval from infection to onset of symptoms) in horses varies between five and 16 days. The case fatality rate in horses is about 75%.
Spill-over of Hendra virus from fruit bats to horses is rare. The transmission route is likely through contamination of pasture or feed by infected birthing fluids or fetal tissues from bats.
Preventing transmission in horses
There is no vaccine against Hendra virus. Routine cleaning and disinfection of horse stables is expected to be effective in preventing infection.
If an outbreak is suspected, the horse premises should be quarantined immediately. Culling of infected animals – with close supervision of the burial or incineration of carcasses – may be necessary to reduce the risk of transmission to people. Restricting or banning the movement of horses from infected stables to other areas can reduce the spread of the disease. As Hendra virus outbreaks in horses have preceded human cases, establishing an animal health surveillance system to detect new cases is essential in providing early warning for veterinary and human public health authorities.
Reducing the risk of infection in people
In the absence of a vaccine, the only way to reduce infection in people is by raising awareness of the risk factors and educating people about the measures they can take to reduce exposure to the virus.
Public health educational messages should focus on the following.
- Reducing the risk of horse-to-human transmission. Protective equipment such as gloves, gowns, masks and protective eyewear should be worn while handling sick animals or their tissues, and during post-mortems.
- Reducing the risk of bat-to-horse transmission. Horse feed and water troughs should be relocated to areas away from where bats feed or roost.
Controlling infection in health-care settings
Health-care workers caring for patients with suspected or confirmed Hendra virus infection, or handling specimens from them, should implement standard infection control precautions.
Samples taken from people or horses with suspected Hendra virus infection should be handled by trained staff working in suitably equipped laboratories.
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