BALB/c mice infection with hybrid Leishmania (V.) guyanensis/L. (V.) shawi showed an intermediate virulence profile compared to parental species infections.

Abstract

Introduction: Hybridization events within the genus Leishmania have been documented; however, their impact on the infection dynamics of hybrids remains poorly understood. In this study, we compared the infection dynamics caused by a hybrid parasite, Leishmania (Viannia) guyanensis/Leishmania (Viannia) shawi, with those caused by its parental species, Leishmania (Viannia) guyanensis and Leishmania (Viannia) shawi, in BALB/c mice.

Methods: Balb/c mice were inoculated with stationary-phase promastigote forms of each parasite. Lesion development and parasite load were monitored longitudinally, and cytokine production was assessed at 35 days post-infection (PI).

Results: The infection with the hybrid parasite induced a more rapid and evident progression, attaining its largest dimension between days 14 and 28 days PI, followed by regression. In contrast, infection with L. (V.) guyanensis resulted in a continuous increase in swelling, whereas L. (V.) shawi caused only mild swelling. Parasite loads in skin and lymph nodes were comparable across groups, though the hybrid parasite exhibited a significant increase in parasite burden from day 35 PI onwards.

Discussion: The immunologic response of hybrid parasite infection was associated with reduced gamma interferon (IFN-γ) and elevated interleukin 4 (IL-4) production compared to parental species and controls (P < 0.05), with no significant differences observed in interleukin 12 (IL-12p40) or interleukin 10 (IL-10). Infection with L. (V.) guyanensis led to decreased IFN-γ in lymph nodes and increased IL-4 production in both skin and lymph nodes, whereas L. (V.) shawi infection did not significantly alter cytokine profiles.

Conclusion: Together, these findings provide important insights into the distinct biological behavior of the Leishmania hybrid parasite and its parental species, underscoring the relevance of hybridization in shaping host-parasite interactions and advancing our understanding of leishmaniasis within complex eco-epidemiological settings.