Researchers in the United States believe they have gained an important insight as to why malaria causes only mild, flu-like symptoms in some individuals but in others causes coma and death.
The explanation could lie in the molecular genetics of Plasmodium falciparum, the parasite that causes the disease, they report on Wednesday in Nature, the British science journal.
Aviv Regev of the Massachusetts Institute of Technology's Broad Institute and colleagues took blood from malaria-infected Senegalese children.
They analysed the proteins expressed by parasites in these samples and compared them with a well-known resource for lab study, the yeast Saccharomyces cervisiae.
The parasite, say the scientists, can be in one of three states as it circulates in the host's blood.
One is that it actively grows, metabolising carbohydrates as a source of energy; the second is a "starvation response" as it seeks other carbon sources for metabolism; and thirdly, a state of stress in the host environment.
"The results reveal a physiological diversity in the in vivo [in-host] biology of the malaria parasite," they write.
This differing response could influence the severity of the disease and the response to drugs, they suggest.
Malaria claims more than a million lives a year -- 800,000 of them African children aged under five -- and sickens hundreds of millions more, according to the World Health Organisation (WHO).