A little known virus is causing a bit of a media panic in Australia at the moment. It’s one that we have only known for 17 years, after its first description in 1994 during an outbreak among 21 horses, and I guess the main reason that Australians took notice in the first place was that at the time the infections threatened to get the Melbourne Cup cancelled. It looks like this :
Hendra belongs to a family of viruses called the paramyxoviridae, these are viruses with a single strand of RNA enclosed by a capsule. The natural hosts (they carry Hendra and it doesn’t make them sick) for these things are fruit bats (flying foxes), and we think that horses occasionally get infected through contact with bolidy fluids or birth products from those bats. Hendra initially causes a flu-like picture after an incubation period of 5-14 days, sore throat, muscle pains, fever, that kind of thing, and then often progresses to death in horses (ca 75% mortality) through either respiratory (a severe lung infection) or neurological disease (meningoencephalitis).
There have been 7 documented cases in humans so far, with 4 deaths. These were all people who had been in contact with infected horses. Curiously, Hendra seems to have the ability to become dormant for a while and then get reactivated, one person died from encephalitis 13 months after the initial infection was diagnosed. The mortality in humans seems to be around 50%. There isn’t a specific treatment or vaccination for Hendra, treatment is purely supportive at this stage.
Today I read in the media that Hendra has been found in a dog that lives on a property with a recent case of Hendra in a horse, and that “crisis talks” are being held in Brisbane.
First of all, there is no documented case of fruit bats infecting anything other than horses directly, not humans, not dogs, not cats. All we know is that humans (and now dogs I guess) can get infected via blood or droplets from horses. There is also no indication of human-to-human or dog-to-dog transmission, something we would really be worried about.
But, this is evolution we are talking about here, and the fact that Hendra initially caused death mainly through lung infections, while we are now apparently seeing more and more brain infections, could suggest that there is genetic diversity in the strain, and that we might see a change in infectiosity and transmittability in the future.
So watch this space, but for now, don’t panic !
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