Australian scientists have taken a key step towards developing a vaccine against malaria, after solving a mystery about how parasites carrying the life-threatening disease infect the human body.
Researchers have spent decades trying to come up with a vaccine to fight malaria, which is spread to millions of people each year by mosquitoes carrying infected parasites that get injected into the human bloodstream via mozzie bites.
Now a major international study led by a group of Melbourne-based scientists has discovered how to stop one of the most deadly malaria parasites - Plasmodium vivax (P.vivax) - in its tracks.
A research team led by scientists from the Walter and Eliza Hall Institute of Medical Research found that P.vivax infects humans by latching on to a type of protein that carries iron to young red blood cells, according to the study published in the prestigious journal Science on Friday.
Once the scientists made that breakthrough in understanding how the parasite enters blood cells, they developed antibodies to stop the whole process.
Lead researcher Associate Professor Wai-Hong Tham described the findings from the three-year study as "quite significant" because working out how to stop the parasite entering blood cells may help pave the way for a vaccine to alleviate P.vivax, the most common malaria parasite in countries outside Africa.
"One of the biggest mysteries has been that P.vivax only invades your young red blood cells," she told AAP.
"People observed this in the 1930s but no one actually understood how it could do it molecularly. What this study does is uncover that mystery."
The next step for the scientists is to carry out more tests on the effectiveness of the antibodies, but clinical trials could be another decade away.
"We are building a case for the next vaccine candidate against P.vivax infection," Assoc Prof Tham said.
Prof Tham's study also involved scientists from the University of Melbourne and La Trobe University as well as others from the US, Britain, New Zealand, Thailand, Brazil and Germany.
Their breakthrough comes after scientists at Queensland's Griffith University successfully tested a vaccine targeting multiple strains and species of malaria among a small group of volunteers in 2017.
Further trials are planned for the PlasProtecT vaccine, which consists of inactivated human malaria parasites which have been prevented from growing and causing a malaria infection.
The World Health Organization is also trialling in Africa another vaccine, Mosquirix, which has shown to provide partial protection against Plasmodium falciparum, the most deadly malaria parasite.
There were 216 million cases of malaria and 445,000 deaths from the disease worldwide in 2016, according to the WHO.
About 16 million cases were caused by the P.vivax parasite.
ALL ABOUT MALARIA
* A potentially fatal infection spread by certain types of mosquitoes in tropical parts of Asia, Africa, Central and South America, the Pacific Islands and Middle East
* It's spread by five types of microscopic parasites, the most common being P.vivax
* The parasites live inside the gut and salivary glands of infected mosquitoes
* When an infected mosquito bites a person, the parasites are injected into their blood
* The parasites infect the person's liver and blood cells
* Symptoms include fever, chills, headache, nausea, vomiting, joint and muscle pain
* About 500 cases of malaria are diagnosed in Australia each year, usually in people who have travelled to malaria-affected countries but didn't take anti-malarial medication
(Source: NSW Health)