WASHINGTON – In the hunt for more effective weapons against malaria, international researchers are exploring a little-studied pathway: killing parasites in the liver, before the illness emerges.
“It’s very difficult to work on the liver stage,” said Elizabeth Winzeler, professor of pharmacology and drug discovery at the University of California, San Diego.
For the latest research, published in the journal Science, scientists dissected hundreds of thousands of mosquitoes to remove parasites inside them.
Each parasite was isolated in a tube and treated with a different chemical compound — 500,000 experiments in all.
Researchers found that certain molecules were able to kill the parasites.
After around six years of work, 631 candidate molecules for a “chemical vaccine” have been identified — a normal vaccine that would allow the body to make antibodies.
“If you could find a drug that you give on one day at one time that will kill all the malaria parasites in the person, both in the liver and in the bloodstream, and last for three to six months … that would be super, but there is no drug like that right now,” said Larry Slutsker, the leader of PATH’s Malaria and Neglected Tropical Diseases programs.
Reducing the number of doses is crucial because many medications available today must be taken over three days, said David Reddy, CEO of Medicines for Malaria Ventures. Often, after the first dose, a child begins to feel better. Parents then keep the other two doses in case another of their children falls ill.
“That has two impacts. First, the child does not get cured properly, and secondly it builds drug resistance,” Reddy said.
Malaria is caused by one-celled protozoa in the Plasmodium genus. Female mosquitoes transmit the parasites when they bite people for a meal of blood (males do not bite).
Then the parasite lodges in the liver and multiplies. After a couple of weeks, the population explodes and parasites run rampant in the blood.
At this stage, fever, headache and muscle pain begin, followed by cold sweats and shivering. Without treatment, anemia and breathing difficulties can follow — and even death, in the case of Plasmodium falciparum, which is dominant in Africa.
The new research offers a “promising path, as long as it last several months,” said Jean Gaudart, professor of public health at the University of Aix-Marseille.
Gaudart said new approaches are necessary because resistance is on the rise in Asia against the most effective treatment using artemisinin, derived from a Chinese plant.
“We really need new compounds,” he said.
Now it is up to researchers to confirm which of the 631 molecules identified have a real shot at wiping out this global scourge.
The World Health Organization said last month that global efforts to fight malaria have hit a plateau, with 2 million more cases of the killer disease in 2017 — 219 million — than the previous year.
Malaria killed 435,000 people last year, the majority of them children under age 5 in Africa.
The first malaria vaccine for children — called RTS,S — will be distributed in thee African countries in 2019, though it only reduces the risk of malaria by 40 percent after four doses.
Despite billions of dollars spent, the world still has not found a real effective solution to malaria.