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

Ana Carolina Stocco Lima^1,2*Thaise Yumie Tomokane¹Gabriela Fernandes Rodrigues¹Larissa dos Santos Alcântara¹Marliane Batista Campos²Maíra Pombo³Marcia Dalastra Laurenti¹Vania Lucia Ribeiro da Matta¹Lucile Maria Floeter-Winter⁴Carlos Eduardo Pereira Corbett¹Fernando Tobias Silveira^2,5Claudia Maria de Castro Gomes¹

• ¹Laboratório de Patologia de Moléstias Infecciosas (LIM50), Departamento de Patologia, Faculdade de Medicina, Universidade de Sao Paulo, São Paulo, Brazil
• ²Secretaria de Vigilância da Saúde, Ministério da Saúde, Instituto Evandro Chagas, Ananindeua, Brazil
• ³Universidade Federal do Amapa Departamento de Ciencias Biologicas e da Saude, Macapá, Brazil
• ⁴Instituto de Biociências, Universidade de Sao Paulo, São Paulo, Brazil
• ⁵Núcleo de Medicina Tropical, Universidade Federal do Para, Belém, Brazil

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. To this end, 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). Our results showed that 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. 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. 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.