Scientist in the United States on Sunday offered a molecular-level explanation for how a Chinese herbal medicine used for more than 2,000 years tackles fever and eases malaria.

The herb is an extract of the root of a flowering plant called blue evergreen hydrangea, known in Chinese as chang shan and in Latin as Dichroa febrifuga Lour.

Chang shan's use dates back to the Han dynasty of 206 BC to 220 AD, according to ancient documents recording Chinese oral traditions.

In 2009, researchers made insights into its active ingredient, febrifuginone, which can be pharmaceutically made as a molecule called halofuginone.

They found that halofuginone prevented production of rogue Th17 immune cells which attack healthy cells, causing inflammation that leads to fever.

A study published in the journal Nature on Sunday found halofuginone works by hampering production of proteins for making "bad" Th17 cells, but not the "good" ones.

Specifically, it blocks molecules called transfer RNA (tRNA), whose job is to assemble a protein bit by bit, in line with the DNA code written in the gene.

As for malaria, halofuginone appears to interfere with the same protein-assembly process that enables malaria parasites to live in the blood, the study said.

"Our new results solved a mystery that has puzzled people about the mechanism that has been used to treat fever from a malaria infection going back probably 2,000 years or more," said Paul Schimmel, who headed the team at the Scripps Research Institute in California.

Halofuginone has been tested in small-scale human trials to treat cancer and muscular dystrophy. Drug engineers also eye it as a potential tool for combatting inflammatory bowel disease and rheumatoid arthritis, which are also autoimmune diseases.