Researchers have discovered how the malaria parasite initiates the process of passing from human to human, unlocking a long-standing mystery.
They have discovered the "master switch" that triggers the development of specialised sexual cells in the parasite that are responsible for the infection of a mosquito and the initiation of transmission.
It is hoped the discovery will open up the way to the development of new drug treatments to prevent transmission of the potentially fatal disease.
The research was carried out by scientists from the University of Glasgow and the Wellcome Trust Sanger Institute in Britain.
Andy Waters, professor and director of the Wellcome Trust Centre for Molecular Parasitology at the University of Glasgow, said malaria was the biggest parasitic disease killer in the world.
"There are drugs, but they are losing their efficacy because the parasite is becoming resistant," he said. "There is currently no vaccine."
Malaria is transmitted to people through the bites of mosquitoes that have themselves been infected by the Plasmodium parasites that cause the disease through a previous blood meal taken from an infected person.
When a mosquito bites an infected person, a small amount of blood is taken in that contains microscopic malaria parasites.
About two weeks later, when the mosquito takes its next blood meal, the progeny of these parasites mix with the mosquito's saliva and are injected into the person being bitten.
The team of researchers have now identified the way the parasite flicks the switch that allows transmission to take place.
Both male and female sexual forms (termed gametocytes) of the malaria parasite are responsible for the infection of the mosquito and initiation of transmission.
The researchers have identified a single regulatory protein that acts as the "master switch" that triggers the development of the gametocytes.
If the malaria parasite is unable to develop gametocytes, then transmission of the disease from one host to another can no longer take place.
The researchers spent more than three years using genome sequencing techniques to identify mutants of the protein that prevent the development of gametocytes; they then effectively reversed the process by genetic engineering the mutant gene in the parasites to repair the protein switch.
The discovery of how the key regulatory protein works means this "transmission switch" could be disabled in future through the development of new drugs.
However, any drug treatment developed as a result of this research is likely to be what scientists describe as an "altruistic intervention", where the drug would be taken by adults who were already infected by malaria but had developed resistance to the disease.
The drug would block the "transmission switch", thus preventing infection to others.
The research is published in the February 23 edition of the journal Nature.
