Lack of relationship on in vitro susceptibility of Leishmania (Viannia) braziliensis promastigotes and Leishmania RNA virus 1 to the trivalent antimonial

Objective: To evaluate the relationship between the presence/viral load of Leishmania RNA virus 1 (LRV1) and the in vitro susceptibility of Leishmania (Viannia) braziliensis promastigotes to trivalent antimony (SbIII). Methods: An experimental study analyzing 20 strains of L. (V.) braziliensis, 12 of which were positive for LRV1. Susceptibility to SbIII was assessed using smoothing curves and the activity index (AI). LRV1 was quantified by real-time PCR (qPCR). Statistical tests were applied to evaluate associations and correlations between the analyzed parameters. Results: The strains were classified as susceptible (N=8) and less susceptible (N=12) based on smoothing curves compared to the reference strain. According to the AI, all strains showed lower susceptibility compared to the reference strain. Among the 12 LRV1-positive strains, 75% had quantifiable viral loads, while 25% were below the quantification limit. LRV1-positive strains exhibited higher parasite density compared to LRV1-negative strains. Conclusion: Although LRV1-positive strains presented higher parasite density, no significant correlation was observed between the presence/viral load of LRV1 and in vitro susceptibility to SbIII.