Daily Archives: 04/07/2011

Pushing back the Hendra virus

It’s worrying.  There has been another outbreak of the Hendra virus in horses in southeast Queensland.  The farms are quarantined, and people who were in close contact with those horses are being tested.

As I understand it as a complete layman in the matter, the Hendra virus infects flying foxes, and kills them.  The virus also infects horses if they eat grass or fodder that has been tainted by an infected bat, and kills them.  Humans can catch the virus from an infected horse, but not, apparently, from a fruit bat, though we are constantly urged not to touch sick bats – ‘just in case’.  It kills humans too.

I live just a few kilometres from Hendra, which gave the virus its name.  There is a racecourse and training stables in my neighbouring suburb of Deagon.  And there is a flying fox colony in Sandgate just behind the railway station – I can see them hanging from the branches as I sit on the platform waiting for trains, and if I come home just on dusk, I see them pour out of the colony, fanning out across the suburb in search of fruit and nectar – and in summer making a beeline for my mango trees.

Grey-headed flying fox

Grey-headed flying fox, Pteropus poliocephalus, photo by Justin Welbergen, courtesy of Wikimedia Commons

Now I know that viruses are constantly evolving and mutating, so it’s quite possible that when the Hendra virus turned up at Hendra in 1994, killing a number of horses, together with their trainer Vic Rail, it was a completely new pathogen.  But as a historian, my instinct is always to look back at the documentary records, to see if there’s any possibility that it was there earlier.

Flying foxes have been in Australia for millions of years – I hesitate to be more specific, because there’s some debate about the origin of these mega-bats.  Some scientists see them as closer to primates than true bats, and I’m simply not qualified to enter the discussion.  But they were certainly the oldest placental mammals to reach the continent, since they were able to do so under their own steam.  The others – humans and, much later, dingoes – had to wait for the invention of the boat.

But there were no horses in Australia before 1788, and none in the Moreton Bay region, the focus of most outbreaks, before the 1820s.  So if a virus deadly to man requires the conjunction of flying foxes and horses – then that date represents the base line.

Flying foxes were an important food source for Aborigines.  Nocturnal animals living in very large colonies, they were relatively easy to catch.  They are eaten throughout the Pacific and South East Asia, and are a delicacy in many societies.

I hadn’t realised until I started looking, though, how closely the early settlers lived with flying foxes.  Watkin Tench, in A Complete Account of the Settlement at Port Jackson (1793), reports that

Governor Phillip saw one which measured upwards of four feet from the tip of each wing. Some were taken alive, and would eat boiled rice, or other food readily out of the hand, and in a few days were as domestic as if they had been bred in the house: the governor had one, a female, that would hang by one leg a whole day without changing its position; and in that pendant situation, with its breast neatly covered with one of its wings, it ate whatever was offered it, lapping out of the hand like a cat.

I haven’t been able to trace a similarly close relationship with flying foxes in the Moreton Bay settlement in the 1820s – by then there were more conventional pets available, and perhaps the habit of scientific enquiry was less developed amongst the convicts and soldiers of Moreton Bay, than amongst the enlightenment officers of Botany Bay, all busily scribbling their memoirs for future publication.

But flying foxes were still an important food source.  In his Journal of an Overland Expedition in Australia in 1845, Ludwig Leichhardt and his companions ate a lot of them as they northern Australia, from the Darling Downs to Port Essington.  On 30 October, for instance,

Charley shot three, and we made a late but welcome supper of them.  They were not so fat as those we had eaten before, and tasted a little strong; but, in messes made at night, it was always difficult to find out the cause of any particular taste, as Master Brown wished to get a quickly as possible over his work, and was not over particular in cleaning them…

Yuck.  The following day they had better luck by daylight – less so for the bats:

Charley and Brown went to shoot flying-foxes, and returned at luncheon with twelve; during the afternoon, they went again and brought in thirty more; having left about fifty hanging, wounded, on the trees.

What about the horses? That day, Leichhardt called a rest day after finding

Brown’s old horse…lying at the opposite side of the creek, with its back down the slope, and unable to move.  We succeeded in turning him, and helping him to rise, but he was so weak, as to be scarcely able to stand…

Clearly the horses were grazing near a flying fox camp – but after weeks of travel, the ‘poor brutes’ were exhausted, so there is no need to look for disease to explain their deaths.

George Catlin, Horses

George Catlin, Horses. In Yale Digital Commons

In fact, when I went looking for references to sick or dying horses in the literature, I was overwhelmed.  There were so many horses in 19th century Australia, and they often lived wretched lives, so that it’s impossible to trace all the many causes of their death.  It defeats me, anyway.

The Americans had a saying that the frontier was ‘Good for men and dogs, but hell on women and horses.’  And so it seems.

Perhaps I’m wasting my time.  Perhaps it’s possible to trace back the origin of a virus from internal evidence alone, without recourse to the historical records.  But I remember in the 1980s, when AIDS was newly discovered and described, having a conversation with Barrie Smith, who worked in medical history.  He mentioned that he had come across a case history in a late 19th century volume of the Lancet, of a Belgian sailor who came home from spending time in the Congo with a mysterious ailment – that seemed remarkably similar to Kaposi’s sarcoma.  It was a cluster of this unusual skin cancer that first led to the identification of AIDS in California.  Only later did it become clear that the virus first emerged from what was then the Belgian Congo.

History can occasionally yield useful information for scientists – if we, and they, have the foresight to talk to each other.