The Hendra Virus: A Dangerous Cross-Species Infection
By Deborah Barkin Fromer
Faculty Member, School of Health Sciences, American Military University
If you follow the news, you are aware bats are hosts to some of the most alarming emerging zoonoses (diseases that can be transmitted to humans from animals) like COVID-19. You may also be familiar with terms such as “cross-species transmission” or the spillover of viruses from bats to other mammals. One particularly dangerous virus for animals and humans is the Hendra virus (HeV).
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What Is The Hendra Virus?
The Hendra virus is a rare zoonosis that causes a severe, frequently fatal infection in horses and is occasionally passed on to humans. The natural host of this virus are fruit bats, sometimes referred to as flying foxes. However, bats infected with the Hendra virus do not show any visible signs of illness.
HeV is a nationally reportable disease in Australia; there is a legal obligation to report cases.
The Hendra virus acquired its name because it was first isolated in a 1994 outbreak in a large racing stable in the Hendra suburb of Brisbane, Australia.
This outbreak involved 21 horses and two humans. Sadly, the infection resulted in the deaths of one of the human cases and 14 of the horses.
From 1994–2010, there were 14 HeV outbreaks in the area. In 2011, outbreaks grew throughout Queensland and New South Wales, and samples from a dog tested positive for HeV.
How Is The Hendra Virus Transmitted?
Horses are grazing animals that generally live in pastures, and trees afford them shade in the outdoors. Scientists have theorized that horses are infected by the Hendra virus when they ingest fruit bat body fluids (such as fluids containing saliva, urine, feces or birthing materials) on partially eaten fruits and flowers.
These half-consumed fruits and flowers drop from bats that are either flying overhead or feeding in trees in pastures where horses graze and drink water. The spread to humans occurs through direct contact with the body fluids of infected horses, such as nasal secretions, saliva, urine or blood products.
Symptoms Of The Hendra Virus For Horses And Humans
In horses infected with the Hendra virus, the onset of the illness is rapid. The Queensland Government in Australia notes that the “early signs can include fever, increased heart rate and restlessness. Other common features may include difficulty breathing and/or weakness and neurological signs such as uncoordinated gait and muscle twitching, quickly leading to death in most cases.”
In humans, the initial symptoms typically develop between five and 21 days after contact with an infected horse. Those symptoms include:
- Sore throat
Over time, meningitis or encephalitis can develop. The human patient may experience convulsions or enter a coma.
Cross-Species Hendra Virus Transmission: How Does It Happen?
The Australian Department of Agriculture and Fisheries believes that the virus can be transmitted from:
- Fruit bat to horse
- Horse to horse
- Horse to human
- Horse to dog
However, there is currently no evidence the virus can be transmitted from:
- Fruit bat to human
- Human to horse
- Human to human
Prevention Of A Hendra Virus Infection
Prevention measures against a Hendra virus infection include keeping horses away from contamination from fruit bat body fluids and quarantining sick horses. A vaccine is available for horses; a vaccine is NOT currently available for humans, so using good hygiene practices when around horses is your best defense.
Infected horses can shed HeV a few days before they show any sign of illness. Recent research has shown there is no evidence recovered horses shed the virus, and euthanasia of recovered horses is no longer mandatory.
To understand and mitigate the threat of the Hendra virus, keep in mind and appreciate the associations between fruit bat, horse and human. The fruit bats may be under stress due to a loss of their traditional habitat (deforestation and other ecological processes), which triggers an alteration in their foraging patterns.
As a result, these disruptions could create more opportunities for spillover events to occur. But meeting this challenge requires an understanding of human behaviors that increase the risk of exposure. For many bat-borne zoonoses, the Hendra virus may typify the spillover process.
About The Author
Deborah Barkin Fromer received a B.S. in biology at the Sage Colleges in Albany, New York and was certified with the American Society of Clinical Pathologists as a medical technologist in 1976. She worked in the clinical laboratory as a medical technologist specializing in microbiology. In the 1990s, Ms. Fromer became interested in public health, returned to graduate school and completed a Master of Public Health (MPH) degree at Wichita State University in Wichita, Kansas.
Ms. Fromer spent several years at the University of Kansas School of Medicine as a researcher in obstetrics and gynecology, and several years as a researcher and teaching associate in preventive medicine and public health. She has taught online epidemiology and public health courses since 2001.
From 2007-2015, Ms. Fromer was an epidemiologist at the Sedgwick County Health Department in Wichita, Kansas. Her work involved electronic surveillance of reportable disease and medical conditions, investigating outbreaks and illness, solving mysteries, and keeping people in the community educated and healthy.