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Researchers have provided the first evidence that malaria parasite development in the always-changing environment of a human host is strikingly different to how it develops in the more consistent surroundings of a laboratory.

The results of their study, published online in Nature today (29 November), may help explain why some patients suffer more extreme symptoms than others.

Researchers from Senegal and the United States screened a number of patients at Velingara Hospital in east Senegal, where malaria is particularly endemic, collecting blood samples from 43 children of varying ages and symptoms.

Subsequent genetic analysis of the malaria parasite Plasmodium falciparum, found in their blood, revealed that each human host had influenced the parasite's physiology and may have had an impact on its virulence, said co-author Daouda Ndiaye, from the Le Dantec teaching hospital in Dakar, Senegal.

The researchers write that there is a "previously unknown physiological diversity" in the biology of malaria in a living organism.

"This is a real advance," Ndiaye said. "Although only 43 patient samples were studied, we identified two new biological states of the parasite." They found that parasites can be actively growing, starving or stressed — with only the first of these apparent when studied in culture.

Co-author Elizabeth Winzeler, from the Genomics Institute of the Novartis Research Foundation in California, United States, said scientists had been making assumptions about the malaria parasite's metabolism based on laboratory observations, which do not correspond to fluctuating circumstances inside a human host.

"This study shows that we should probably not make such assumptions and that the physiology of parasites inside of people may be different than their physiology inside of laboratory flasks. The work may point to why some drugs do not work as expected in curing disease," she told SciDev.Net.

The study will aid malaria drug development and improves the chance of developing a malaria vaccine, Winzeler added. "This could result in more effective drug combinations, which target both physiological states [in human hosts and laboratory conditions] simultaneously. Better drug combinations would reduce the threat of drug resistance emerging."

Link to full paper in Nature

Reference: Nature doi 10.1038/nature06311 (2007)