Extracellular vesicles in parasitic protozoa: Impact of Leishmania exosomes containing Leishmania RNA virus 1 (LRV1) on Leishmania infectivity and disease progression.

This chapter focuses on the interplay between Leishmania parasites and their host, particularly on Leishmania RNA virus (LRVs) and extracellular vesicles (EVs) in modulating host-pathogen interactions. Leishmania EVs have been shown to facilitate gene transfer, including drug-resistance genes, enhancing the parasites' survival and resistance to antileishmanial therapeutics. These EVs also play a significant role in host immune modulation by altering cytokine production in macrophages and promoting an anti-inflammatory environment that favours parasitic persistence. The presence of virulence factors such as GP63 within these EVs further underscores their role in the parasite's immunopathogenesis. Over the last few decades, LRVs have been established as drivers of the severity and persistence of leishmaniasis by exacerbating inflammatory responses and potentially influencing treatment outcomes. This chapter discusses the evolutionary origins and classification of these viruses, and explores their role in parasitic pathogenicity, highlighting their ubiquity across protozoan parasites and their impact on disease progression.