In a continuing quest for more effective weapons against malaria, international researchers said on Thursday they are exploring a path that has so far been poorly studied – killing parasites in the liver, before the disease appears.
"It's very difficult to work on the liver stage," said Elizabeth Winzeler, a professor of pharmacology and drug discovery at the University of California, San Diego School of Medicine.
"Traditionally, we are looking for medicines that cure malaria," she told AFP.
For the latest research, published in the journal Science, scientists have dissected hundreds of thousands of mosquitoes to remove parasites inside them.
Each parasite was then isolated in a tube and treated with a different chemical compound – 500,000 experiments altogether.
The researchers found that certain molecules were able to kill the parasites.
After about six years of work, 631 molecules candidates for a "chemical vaccine" were identified – a normal vaccine that would allow the body to produce antibodies.
"If you could find a drug you administer on a day at a time, it will kill all the malaria parasites in the person, both in the liver and in the bloodstream, and it will last three to six months.Yes, that would be super, but there is no such drug right now, "said Larry Slutsker, leader of PATH's Malaria and Neglected Tropical Diseases (NTDs) programs.
Reducing the number of doses is crucial.
That's because many medications available today should be taken over three days, said David Reddy, CEO of Medicines for Malaria Ventures.
But often, after the first dose, the child begins to feel better and the fever subsides. The parents keep the other two doses if another of the children gets sick.
"This has two impacts: First, the child is not properly cured, and second, it builds resistance to the drugs," Reddy said.
The disease develops
Malaria is caused by a tiny parasite called Plasmodium.
Female mosquitoes transmit the parasite when they bite people for a meal of blood (males do not bite).
Then the parasite lodges in the liver and multiplies. After a few weeks, the population explodes and the parasites run free in the blood.
At this stage, fever, headache and muscle aches begin, followed by cold sweats and tremors. Without treatment, anemia, breathing difficulties and even death can occur in the case of Plasmodium falciparum, which is dominant in Africa.
The research published on Thursday offers a "promising path for as long as several months," said Jean Gaudart, a professor of public health at the University of Aix-Marseille.
Gaudart said new approaches are needed because resistance is increasing in Asia against the most effective treatment using artemisinin, derived from a Chinese plant.
"We really need new compounds," he said.
It is now up to the researchers to confirm which of the 631 molecules identified have a real chance of annihilating this global scourge.
The World Health Organization (WHO) said last month that global efforts to fight malaria reached a plateau, with two million more cases of fatal disease in 2017 – 219 million – than in the previous year.
Malaria killed 435,000 people last year, most of them children under five in Africa.
The first malaria vaccine for children – called RTS, S – will be distributed in African countries in 2019, although it will reduce the risk of malaria by 40% after four doses.
Despite the billions of dollars spent, the world has not yet found an effective solution to malaria.