Leishmania (Viannia) spp. can harbor a double-stranded RNA virus known as Leishmania RNA virus 1 (LRV-1), whose presence has been reported in nine countries across the Americas and seven Leishmania species. Here, we studied 100 Leishmania (Viannia) isolates from patients with cutaneous leishmaniasis collected from different endemic areas in Panama from 2016 to 2022. We identified L. (V.) panamensis, L. (V.) guyanensis, L. (V.) braziliensis/guyanensis hybrid, and L. (V.) panamensis sp.1. (genetic variant). LRV-1 was detected by RT-PCR in 9% of L. (Viannia) isolates (eight cases in L. (V.) panamensis, and one in L. (V.) guyanensis). Phylogenetic analysis based on sequencing data classified all LRV-1 isolates within genotype A, suggesting that LRV phylogenetic proximity is closely aligned with geographical distribution or to the phylogenetic proximity of the Leishmania host in the case of the L. (V.) panamensis and L. (V.) guyanensis in Panama.

Leishmania RNA virus 1 (LRV-1) is a double-stranded RNA virus identified in several Leishmania spp. LRV-1 has been associated with increased disease severity and therapeutic failure in cutaneous leishmaniasis (CL). Although LRV-1 has been reported in the Americas, its influence on parasite infectivity and host immune responses remains poorly characterized in Panamanian isolates. In this study, we investigate the in vitro infectivity and immunomodulatory effects of LRV-1-positive (LRV-1⁺) versus LRV-1-negative (LRV-1⁻) isolates of Leishmania (Viannia), including clinical strains of L. (V.) panamensis and L. (V.) guyanensis. A total of 21 isolates (nine LRV-1⁺, nine LRV-1⁻, and three reference strains) were used to infect human U937 macrophages. The infectivity index (II) was measured at 24, 48, and 72 h post-infection. Cytokine levels of TNF-α, IFN-γ, IL-4, IL-6, IL-10, and IL-17 were quantified by flow cytometry, and IL-1β by ELISA at 24 and 48 h. LRV-1⁺ isolates exhibited significantly higher infectivity at 48 h (mean II = 1386.2) and 72 h (mean II = 1316.8) compared to LRV-1⁻ isolates (mean II = 714.4 and 571.0, respectively; p < 0.001). Two L. (V.) panamensis LRV-1⁺ isolates associated with complicated CL cases displayed the highest II values. Cytokine analysis revealed that LRV-1⁺ isolates induced elevated TNF-α (p < 0.01) and IL-1β (p < 0.001), along with reduced IFN-γ (p < 0.01), while no significant differences were observed for IL-4, IL-6, IL-10, or IL-17. These findings indicate that LRV-1 enhances parasite infectivity and promotes a pro-inflammatory cytokine profile, which may contribute to disease persistence and treatment failure.