Hendra virus Q and A

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Hendra virus

What is Hendra virus?

Hendra virus was first isolated in 1994 following an outbreak in a racing stable in the northern Brisbane suburb of Hendra.

It resulted in the death of horse trainer Vic Rail and 13 horses. A stable hand became seriously ill. Seven other horses with evidence of exposure were euthanized, in a policy which continues to this day.

It was originally classified as a Morbillivirus, but has been reclassified as Hendra Virus (HeV). It belongs to a new genus (Henipavirus) in the family Paramyxoviridae.

How common is it?

Infection is extremely rare in horses and even rarer in people, who can catch it from horses. Evidence suggests that Hendra virus is carried by Australian fruit bats. Screening has shown antibodies to Hendra virus in all four species of flying fox occurring on mainland Australia. Follow-up studies showed an antibody prevalence of between 20-50% in flying fox populations across their mainland distribution. These findings indicate that flying foxes are a natural host. Six of the 12 cases in 2008 involved just one horse catching the virus.

How do horses catch it?

The precise mechanism is still under investigation. It is possible that contact with or ingestion of bat droppings or urine may play a part, even saliva. There is a further suggestion that contact with birth byproducts may also play a part.

Restraint of an adult Flying Fox using a towel.
Restraint of an adult Flying Fox using a towel. © Andrew Breed/Aust DAFF

Evidence suggests the virus spreads easily between bats, but they show no clinical signs and appear to be unaffected by the virus. It is probably significant that the first cases in any horses have always been among those held in yards or paddocks, not stalls. Horses are able to pass the virus on to people. There is a possibility that horses can pass it to each other, but no evidence has emerged of human to human transmission, or bat to bat transmission.

How do humans catch it?

It appears to require close contact with the body fluids of infected horses. Recent evidence suggests horses can excrete the virus through nasal secretions up to two days before showing signs of infection. That said, evidence suggests that the sicker the horse, the more virus it is shedding. The virus does not appear to survive long outside its host, so a victim would need to be exposed to infected material when it is still fresh.

Can people catch the virus directly from fruit bats?

There is no indication of significant risk. Scientists tested 130 people, all of whom had close contact with flying foxes, and found no evidence of the virus. That said, members of the public are advised against handling fruit bats.

Can people catch the virus from fruit bats?

There is no indication of significant risk. Scientists tested 130 people, all of whom had close contact with flying foxes, and found no evidence of the virus. That said, members of the public are advised against handling fruit bats.

How dangerous is Hendra?

It kills more than 70 per cent of horses it infects. Of the six people who have been infected by Hendra, three have died.

What is the focus of Hendra research? Developing better outbreak prevention and control measures, and possible vaccines and treatments. Given that flying foxes are the natural host, research in the field is difficult. There remain unanswered questions over how and when the virus is transmitted from bats to horses, and even whether other animal vectors may be involved.

What are the symptoms?

It causes an influenza-like illness, with severe lung damage and accumulation of massive amounts of fluid. In even more severe cases, there is inflammation of the brain, called encephalitis.

What is the incubation period?

It is likely to be five to 15 days before symptoms appear. Horses die, on average, just two days after the the first symptoms appear.

Can animals other than bats, horses and humans catch the virus?

Scientists have tested a number of animals in a bid to identify other possible vectors. Mice, rats, rabbits, chickens, and dogs have been given the virus but did not develop disease. However, cats and guinea pigs are highly susceptible. This raises the possibility that even cats could play a role in transmitting the virus, but there has been no evidence of natural infection of cats.

What treatments are available?

There are no vaccines at this stage and any are likely to be some years away.

 

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