THE key to unlocking the mysteries of the Hendra virus lies in the protected flying foxes which host the deadly disease.
It is not known exactly how these seemingly harmless mammals transmit the virus to horses but scientists are fairly sure the native bats are the source. The mortality rate in horses is more than 70 per cent yet bats appear to be unaffected.
The latest victim of the virus, Rockhampton veterinarian Alister Rodgers, whose funeral was held on Thursday, was exposed to the bodily fluids of a horse at a Cawarral stud near Rockhampton on July 28 where three other horses also contracted the virus. This week a Bowen hobby farm in north Queensland and three neighbouring properties were quarantined after a horse tested positive to the virus. That horse and two others were destroyed and 18 horses on the neighbouring properties are being tested for the virus, along with 10 people.
Stephen Prowse, chief executive of the Australian Biosecurity Co-operative Research Centre for Emerging Infectious Disease, said while horses probably contracted the virus from bat secretions in their troughs, “the exact process is still a bit unclear”.
“There does appear to be a correlation between outbreaks and bat breeding season in late winter (and) spring,” Dr Prowse said. One hypothesis was that bats, like other mammals, could be more susceptible to diseases during pregnancy due to low immunity. Loss of natural habitat and drought have brought the native fruit bats into urban areas, closer to horses and humans. Dr Prowse said while there was no reported bat-to-human transmission, it could not be ruled out.
But he labelled calls to cull the protected native bats “misguided and alarmist”. The likelihood of people coming in contact with a bat secreting the virus was minuscule. “Of the hundreds of bats tested for the virus in the bat trapping studies, only two or three . . . have been found to be shedding the virus,” Dr Prowse said.
“People shouldn’t be alarmed – this is an extremely rare disease.”
Biosecurity Queensland deputy chief veterinary officer Rick Symons said Dr Rodgers’s death, the fourth from the disease, was a tragic reminder to people who worked with horses that they needed to protect themselves. Dr Symons said before Hendra virus emerged, there were very few diseases that humans could catch from horses.”People are very fond of having horses – they are their companions and their pets (and) people want to get close to them,” he said.”But they need to change how they look at horses now, and sick horses are a potential source of Hendra virus and people need to take precautions for it.”
Dr Prowse predicted a vaccine for horses was at least five years away and one for humans would take even longer.”It will cost in the tens of millions, if not hundreds of millions, to get a vaccine on the market,” he said.”But (the research) needs to be underwritten by government agencies because companies aren’t going to spend the money on a vaccine for such a relatively small market.”
Hendra virus – the facts – Its effects
* The virus predominantly infects the cells which form the inside layer of blood vessels.
* The infection can cause small blood vessels, which supply oxygen to the body, to become obstructed.
* In the lungs, this can cause respiratory problems, and the brain can become inflamed, resulting in headaches, drowsiness, convulsions and coma.
* Current medical treatment includes intravenous therapy and mechanical ventilation.
* Humans contract the disease after being exposed to an infected horse’s bodily fluids.
* Symptoms in humans have included an flu-like illness which can progress to pneumonia; or encephalitis, an inflammation of the brain which can cause headaches, high fever and drowsiness.
* Symptoms in horses have included raised temperature and heart rate, flu-like respiratory symtoms and unsteadiness on their feet.
* There is currently no vaccine against Hendra virus and no proven anti-viral treatments.
What we don’t know
* How or even if the virus is transmitted from bats to horses. Most likely horses ingest bat secretions in their food or water.
* Why most horse infections occur during bat breeding season.
* The exact incubation period, particularly in humans. Estimates are five to 22 days.
* All the symptoms in horses or humans – they can be very mild to severe.
* Why some horses and humans recover and others die.
* Why the virus spilled over from bats to horses and humans, despite the bats carrying the disease for tens of thousands of years.
* Why rodents and cats can be given the virus in the laboratory but not catch it in the wild.
What we know
* Four of the seven people who have contracted the virus have died.
* All human infections have occurred after direct exposure to the secretions or tissues of infected or dead horses.
* Flying foxes infected with Hendra virus appear to be unaffected.
* The disease was discovered in Queensland in 1994. this
* There have been 13 reported outbreaks of Hendra virus infection in horses.
* The reported mortality rate in affected horses is more than 70 per cent.
* No other animal is known to be infected naturally.
* There is no evidence of human-to-human spread or human-to-horse spread of Hendra virus.
* Although Hendra virus does not appear to be highly contagious, humans and horses are susceptible to the disease.
* Hendra virus was isolated in 1994 from specimens obtained during an outbreak of respiratory and nervous system disease in horses and humans in the Brisbane suburb of Hendra. Trainer Vic Rail died, along with up to 20 of his thorouoghbred racehorses.
* Hendra is closely related to Nipah virus which emerged in pigs and humans in Malaysia in the late 1990s and has killed more than 240 people in Malaysia, Singapore, Bangladesh and India.
Under Queensland legislation if you suspect a horse has Hendra virus you must report it to Biosecurity Queensland.