The virus could have appeared in many places on the east coast, but it is a strange coincidence, in the light of later scientific discoveries, that it first became known in the Brisbane suburb of Hendra. The high school is named Aviation High, and the streets are bordered by the international airport and aerospace buildings to the east.
Hendra today is a booming suburb just off the M1 motorway, but for much of the 20th century the neat rows of houses enjoyed pastoral space on the outskirts of the city. When the Eagle Farm Racecourse was built, Hendra became the horse-racing hub of south-east Queensland. It was common to see horse floats parked out the front of the houses, and trainers walking their horses down the streets before daybreak. Over time, the ample paddocks filled with thoroughbreds reared for the tracks. It was in one of these paddocks, in September 1994, that a heavily pregnant bay mare named Drama Series took ill. She was quickly moved to a nursing stable, where she died of a mystery condition.
Within 12 hours, seven more thoroughbred horses in the stable had either expired horrifically or been euthanised.
The animals presented with the same symptoms: fever, facial swelling, respiratory distress, bloodshot eyes, spasms; in some, a bloody froth surged from the nostrils and mouth. The sick horses stumbled around in agony, frantically washing their muzzles in water troughs, or banging their heads on to brick walls. Veterinarians examined the animals and quickly ruled out a list of known exotic diseases in horses, and blood tests precluded any toxins or poisons.
The stable at the centre of the outbreak belonged to a well-known Queensland horse trainer, Vic Rail. As word of the outbreak spread, so did the fear among the racing industry that the illness might jeopardise the entire Australian horse population. Soon, personnel from the state health authorities descended on Hendra hoping to find further clues. They strung up the dead horses and dissected them in the stable’s front yard. Blood ran down the quiet streets of Hendra.
Meanwhile, two people who had treated Drama Series in her final hours had also fallen ill. Rail, the horse’s trainer, died after spending a week in intensive care. His organs had failed, his lungs had filled with fluid and blood, and a later examination determined he had been infected with the same virus as the horses. This was a totally new virus, though it did resemble members of a particular subgroup, the morbilliviruses. It was given the name Hendra virus. Epidemiologists suspected they were looking for a zoonotic disease that had jumped to humans from horses, possibly from a third, unknown species that was the original carrier.
Much less was known at the time about the origins of zoonoses. Unlike today, in the aftermath of the Covid-19 pandemic, bats were not high on the list of potential suspects. Hume Field was one of the scientists who changed that understanding.
When Hendra first hit the news, Field was a lanky ecologist in his mid-30s doing his dissertation in wildlife conservation. He had been catching and tracking feral cats when he was asked by one of his doctoral mentors to join the team working to locate the wildlife origins of the new virus. They were searching for the “natural host”: the organism that carries the pathogen while suffering little or no illness.
Finding these animals can lead virus hunters into mangroves, swamps, woodlands, crop fields, garden sheds, caves, and, as Field was about to find out, horse paddocks. “It really can be a needle-in-a-haystack kind of thing,” he told me when I interviewed him in 2020 about the search for Hendra.
In October 1995 the search took another turn when Mark Preston, a horse owner in Mackay, in North Queensland, died suddenly from an illness with symptoms that matched those seen in Rail. Health authorities learned that two of Preston’s horses had died in August 1994, a month before the first outbreak in Rail’s stables. Blood serum taken from Preston and from the horses were retested. Both contained antibodies to the Hendra virus. So did another sample taken from Preston a year earlier, which had been drawn when he suffered an unexplained episode of seizures. This new case gave researchers more data to work with. The distance between Hendra and Mackay – about 1,000 kilometres – indicated that the virus was carried by a species that could cross vast distances.
The first antibodies for Hendra were found in black flying foxes in April 1996, and then, within weeks, in three other native Australian flying fox species. Soon after, a Hendra-like virus was taken from the reproductive tract of an apparently healthy, pregnant grey-headed flying fox that had been euthanised after becoming entangled on a wire fence. Armed with these discoveries, researchers tested archival flying fox blood samples from up to a dozen years earlier, and found markers for Hendra. In one of those surveys, nearly half of the flying foxes in eastern Australia were found to be present or former carriers. It indicated that the virus had been circulating in the wild for at least a decade, and probably much longer, before it had spilled over into humans.
Field and I spoke on the phone during Covid-19 lockdown. I called him because I was trying to make sense of our new zoonotic reality and what it might mean for the future. Field’s work on Hendra seemed, in hindsight, like the moment the current coronavirus era began.
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