Researchers said Wednesday they had discovered a unique microscopic channel through which malaria parasites must pass to infect red blood cells, a finding that opens up a highly promising target for a vaccine.

The doorway mechanism is common to all known strains of the deadliest mosquito-borne pathogen, Plasmodium falciparum, which means that a future vaccine could in theory work against all of them, according to the study published in the journal Nature.

The death toll from malaria has declined by a fifth over the last decade, but the disease still claims some 800,000 lives every year, mostly children under five in sub-Saharan Africa.

"Our findings were unexpected and have completely changed the way in which we view the invasion process," said Gavin Wright of the Wellcome Trust Sanger Institute and the study's senior co-author.

The breakthrough "seems to have revealed an Achilles' heel in the way the parasite invades our red blood cells."

Up to now, scientists assumed that P. falciparum had several options for piercing the defences of blood cells.

But in experiments, Wright and colleagues showed that intrusion depends on the interaction between a specific molecule on the parasite, called a ligand, and a specific receptor on the blood cell.

Blocking this interaction repels the pathogen's attempt to breach the cell's protective wall, they found.

"By identifying a single receptor that appears to be essential for parasites to invade human red blood cells, we have also identified an obvious and very exciting focus for vaccine development," said co-author Julian Rayner, also from the Sanger Institute.

Early results from clinical trials in Africa showed that the world's first malaria vaccine, reported in a study last month, cut infection rates by roughly half. The vaccine, made by the British pharmaceutical giant GlaxoSmithKline, works by triggering the immune system.

"These reports are encouraging," said Adrian Hill, a researcher at Oxford's Jenner Institute. "But in the future more effective vaccines will be needed if malaria is ever to be eradicated."

Hill added: "The discovery of a single receptor that can be targeted to stop the parasite infecting red blood cells offers the hope of a far more effective solution."