Australian Teams Unlock Malaria’s Deadly Secrets
For more than 70 years, scientists have been puzzled by the strange behaviour of a lethal strain of malaria rampant in the Asia-Pacific region and in particular Papua New Guinea.
Why does it remain dormant and undetected for years, before finally springing into action? Why, unlike other strains, does it select only the youngest red blood cells to infect?
Now, with the aid of a particle accelerator the size of a football field, two Australian research teams believe they have cracked the parasite’s code – and developed a potential vaccine to stop it in its tracks.
“Fundamentally, from a basic science point of view, I think we’ve answered one of the big mysteries,” says Wai-Hong Tham, of the Walter and Eliza Hall Institute, who led one team.
Malaria is a blood-borne parasite spread by mosquitoes, and it comes in several different strains. Plasmodium vivax is considered the second most dangerous, with about 8.5 million cases and about 3100 deaths in 2015, according to the World Health Organisation.
But it operates very differently to its cousin Plasmodium falciparum. It is capable of hiding, inactive, in the liver for several years before exploding into a full-blown infection. And it infects only the youngest red-blood cells.
It is this preference that may ultimately be P. vivax’s undoing.
Associate Professor Tham’s team enlisted the help of the Australian Synchrotron, a huge particle accelerator based in a huge building in Clayton in Melbourne’s south-east.
The synchrotron accelerates particles to close to the speed of light, forcing them to emit extremely powerful light, which can be used for imaging unimaginably small things.
Associate Professor Tham wanted to look not at the parasite – already very hard to see under a microscope – but at the individual atoms that make up the proteins it uses to infect cells.
“An optical microscope is not high-resolution enough; we needed atomic resolution,” she says.
Under the synchrotron’s bright light, P. vivax’s trick became clear. The parasite looks for a “hook” on red blood cells that they use to catch iron in the blood.
Only the youngest red blood cells have these protein hooks. The parasite has its own hook, specially shaped for just this job. It can cling onto the edge of the cell’s hook without disrupting the iron.
When the cell pulls the iron inside itself, the parasite gets pulled in too, Associate Professor Tham theorises.
The parasite’s selection of protein is crafty.
“It’s a very cunning parasite,” says Associate Professor Tham. “Transferrin-receptor is really crucial for human biology. It has cunningly chosen this protein that humans cannot get rid of. We cannot evolve away from it.”
When the team discovered how the parasite operated, they started working on how to kill it.
The protein P. vivax uses to hook onto the red blood cells was extracted and given to mice, which generated antibodies – a similar process to human vaccination.
Those mouse antibodies were then extracted and tested on samples of infected human blood. And, in research published in Science on Friday, the scientists showed they worked, effectively blocking the parasite’s ability to hook onto red blood cells.
By coincidence, just down the road at the Burnet Institute in Melbourne, a second team led by James Beeson was working on the same problem.
Its research turned up a second protein hook that P. vivax uses, and its antibodies also blocked the parasite – suggesting, says Professor Beeson, that more than one hook is required.
“It needs to unlock several locks before it gets into the red blood cell,” he says.
“We think it needs to first grab the cell, then get itself into position, then finally haul itself into the cell.”
For years P. vivax research was “neglected”, says Professor Beeson. But now, thanks to the two breakthroughs, “we have three or four really promising vaccine candidates to work with”, he says.