Viruses are everywhere. These relatively simple yet extremely efficient obligated parasites found ways of infecting pretty much any life form. But did you know that they can also infect other parasites? In a recent study1 led by a team at the University of Sidney, a novel RNA virus has been described living inside malaria parasites.

Using total RNA sequencing of human blood from patients with malaria, the researchers found a virus in Plasmodium vivax, the species causing benign tertian malaria. It has been named Matryoshka RNA virus 1 (MaRNAV-1) for a very good reason: a parasite inside another parasite which lives inside an animal, like a set of three russian dolls. Further analysis revealed that this virus is seemingly very specific to P. vivax (it was not found in samples containing other human malaria species) and belongs to the group of narnaviruses, which are considered by many the simplest viruses described so far.

Despite this being the first description of a virus infecting Plasmodium parasites, the presence of viruses in protozoa has been observed as early as the 60s through electron microscopy. Some have been found inside amoebas2 in a variety of environments: one in particular, called Medusavirus, has been recently described from hot springs. Other viruses infect parasites causing important diseases such as giardiasis, cryptosporidiosis and leishmaniasis. Furthermore, in some instances the virus seems to affect the parasite-host interactions with important consequences for disease severity3.  

It is not yet known whether MaRNAV-1 can affect Plasmodium biology and malaria, but exciting times are ahead with potentially many more viruses of this kind awaiting to be discovered.

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[1] Charon J, Grigg MJ, Eden J-S, Piera KA, Rana H, William T, et al. (2019) Novel RNA viruses associated with Plasmodium vivax in human malaria and Leucocytozoon parasites in avian disease. PLoS Pathogens 15(12): e1008216. DOI: 10.1371/journal.ppat.1008216

[2] Aherfi S, Colson P, La Scola B and Raoult D (2016) Giant Viruses of Amoebas: An Update. Frontiers in Microbiology 7: 349. DOI: 10.3389/fmicb.2016.00349

[3] Ives A, Ronet C, Prevel F, Ruzzante G, Fuertes-Marraco S, Schutz F, et al. (2011) Leishmania RNA virus controls the severity of mucocutaneous leishmaniasis. Science 331: 775–778. DOI: 10.1126/science.1199326