The Peculiar Evolution of Malaria Parasites
In 2018, there were an estimated 228 million cases of malaria, and over 405,000 deaths globally [1]. My research is on drug delivery for the radical cure of Plasmodium vivax malaria. Radical cure just means that the treatment can eliminate all of the parasites that reside in the liver! P. vivax is 1 of 5 species of Plasmodium known to cause malaria in humans, but different species of Plasmodium can infect other animals, from lizards to antelopes to birds [2, 3, 4]. I’ve learned a lot about malaria over the past 20 months, but one of the stranger things I’ve read about is about the evolution of the malaria parasite. There is evidence that this parasite which has haunted humankind for tens of thousands of years might have evolved from algae! Or at least, they may share an early algae-like ancestor with algae. In the 90s, scientists discovered that many parasites of the apicomplexa phylum (the phylum that malaria parasites fall under) have a plastid-like organelle. Plastids are typically associated with plants- they are green little compartments where photosynthesis can occur. These vestigial plastids in apicomplexans are called apicoplasts, and they have lost the ability to photosynthesize, but they retained enough ancestral DNA to be linked back to photosynthetic plastids. This article from Nature Education does a great job of hashing out the decades of work that led to this discovery [5].
So how did this apicoplast come to be? Scientists hypothesize that it is the product of secondary endosymbiosis. Endosymbiosis is when an organism lives inside another organism’s body or cells. A well-known example of this is the presence of nitrogen-fixing bacteria in the root nodules of legumes. With apicoplasts, it is believed that at some point long ago, a cyanobacterium (a photosynthetic bacterium) was engulfed by a eukaryotic cell, but instead of being digested, it formed a symbiotic relationship with the cell. This was the primary endosymbiotic event and this new organism would become a photosynthetic alga. At some point, that organism was consumed by another eukaryotic organism, and again it would have formed a symbiotic relationship that preserved the alga as a plastid. This was the secondary endosymbiotic event. This organism would beget a number of taxa, including the Plasmodium parasites.
Over the years, the apicoplast has lost the ability to photosynthesize, but it remains important for the propagation of malaria parasites; without this organelle, the parasite dies. This makes the apicoplast a noteworthy target of potential antimalarial drugs! Two of the most worrisome species of Plasmodium, P. vivax and P. Falciparum, have shown resistance to current antimalarials, so the discovery of novel treatments is necessary. Some research has been done to target the apicoplasts, which would ideally not harm human cells [6,7].
My research doesn’t involve targeting the apicoplast, but it is important for scientists to learn all about their topic, regardless of how relevant we may think the information is to our research.
Citations:
World Malaria Report 2019. Geneva: World Health Organization 2019.
Schall JJ. Lizards infected with malaria: physiological and behavioral consequences. Science. 1982 Sep 10;217(4564):1057-9. doi: 10.1126/science.7112113.
Templeton TJ, Martinsen E, Kaewthamasorn M, Kaneko O. The rediscovery of malaria parasites of ungulates. Parasitology. 2016 Oct;143(12):1501-8. doi: 10.1017/S0031182016001141. Epub 2016 Jul 22. PMID: 27444556.
Valkiūnas G, Iezhova TA. Keys to the avian malaria parasites. Malar J. 2018;17(1):212. Published 2018 May 29. doi:10.1186/s12936-018-2359-5
Laura Vargas Parada, Ph.D. (Biology Dept., School of Sciences, National University of Mexico) © 2010 Nature Education
Saremy S, Boroujeni ME, Bhattacharjee B, Mittal V, Chatterjee J. Identification of potential apicoplast associated therapeutic targets in human and animal pathogen Toxoplasma gondii ME49. Bioinformation. 2011;7(8):379-83. doi: 10.6026/97320630007379. Epub 2011 Dec 21. PMID: 22347778; PMCID: PMC3280436.
Fichera ME, Roos DS. A plastid organelle as a drug target in apicomplexan parasites. Nature. 1997 Nov 27;390(6658):407-9. doi: 10.1038/37132. PMID: 9389481.