Quiescence

How does a vampire avoid that which kills him? He plays dead.

Plasmodium falciparum, a deadly disease known as malaria, proves just as apt to play dead as a fictive vampire facing the sunlight. Humans had a secret weapon against malaria. "Artemisinin (ART), a substance extracted from a Chinese plant," was "the first-line drug for malaria," since other compounds lost their efficacy from overuse and parasite mutation. Artermisinin-based Combination Therapies (ACT) were "the most effective treatment for malaria, achieving a 95% cure rate."

Then, malaria played dead.

In July 2009, artemisinin-resistant malaria was identified in South East Asia. Scientists, desperate to determine how malaria avoided their once brutal weapon, ran laboratory studies.

Françoise Benoit-Vical and his team at Laboratoire de Chimie de Coordination (CNRS) "sought to isolate ART-resistant strains in an experimental manner. This feat was achieved at the end of 2009 when the scientists managed to obtain a strain of Plasmodium falciparum that was resistant to this compound and some of its derivatives, and the first to be adapted to in vitro culture." In the process, the "researchers also identified and characterized a new mode of parasite resistance. To evade the action of ART, Plasmodium falciparum arrested its development and entered a so-called state of quiescence [temporary inactivity]. It thus functioned at a slow metabolic rate until the drug was eliminated", at which time, it would reawaken and wreak havoc again.

"Malaria still continues to kill nearly a million people each year throughout the world. There is no vaccine against this infectious disease", which is caused by a blood parasite and transmitted by mosquitoes."

This study demonstrated "a novel resistance mechanism" and provides "important tool that will allow a clearer understanding of the mechanisms of resistance to antimalarial drugs". Scientists plan further studies in order to "identify the genes responsible for the acquisition of ART resistance."

Sources:
Physorg.com. "How the parasite responsible…" 5 May 2010. http://www.physorg.com/news192300284.html
Witkowski B, Leličvre J, López Barragán MJ, Laurent V, Su XZ, Berry A, Benoit-Vical F. "Increased tolerance to artemisinin in Plasmodium falciparum is mediated by a quiescence mechanism." Antimicrobial Agents and Chemotherapy. Mai 2010.