BACKGROUND: Trypanosomatids are parasitic flagellates best known for human pathogens causing sleeping sickness, Chagas disease, and leishmaniasis. RNA viruses infecting these protists have recently gained attention for their role in disease severity. While numerous such viruses have been described in Leishmania and several other trypanosomatid genera, none has previously been documented in the iconic genus Trypanosoma. RESULTS: We report the first discovery and molecular characterization of RNA viruses in trypanosomes, identifying a leishmaniavirus and two narnaviruses in a single strain of Trypanosoma platydactyli, a parasite of the common wall gecko. The leishmaniavirus genome revealed a conserved organization, including a putative ribosomal frameshift site and a hairpin-like secondary structure typical of the genus. Phylogenetic inference indicates that it is closely related to leishmaniaviruses from Old World Leishmania spp., consistent with shared vector ecology. The two narnaviruses have distinct origins, although both cluster with viruses of other trypanosomatids, suggesting historical exchanges among co-infecting parasites. CONCLUSIONS: Our study expands both the known diversity of RNA viruses in trypanosomatids and the range of trypanosomatid genera that host these viruses, providing guidance for future screening. We suggest that vector ecology-particularly feeding behavior-may influence viral acquisition by trypanosomes, explaining the previous absence of viral reports from intensively studied trypanosomes of medical relevance vectored by tsetse flies or kissing bugs. Therefore, overlooked species transmitted by Nematocera represent promising candidates for future viral discovery. This concept extends beyond trypanosomatids, providing a general framework for understanding the conditions that permit viral host switching by viruses among microeukaryotes.

Central European Institute of Technology Masaryk University Brno 60177 Czechia

Department of Parasitology Faculty of Science Charles University Prague 12800 Czechia

Department of Veterinary Medicine University of Bari Valenzano Bari 70010 Italy

Faculty of Science University of South Bohemia České Budějovice 37005 Czechia

Institute of Parasitology Biology Centre Czech Academy of Sciences České Budějovice 37005 Czechia

Life Science Research Centre Faculty of Science University of Ostrava Ostrava 71000 Czechia

Zoological Institute Russian Academy of Sciences St Petersburg 199034 Russia

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