Progression of Leishmania Amazonensis Infection in the Skin and Liver of C57bl/6 Mice

Leishmaniases are vector-borne infections caused by parasites of the genus Leishmania , with cutaneous or visceral manifestations depending on host immunogenetic profile and species involved. In Brazil, Leishmania amazonensis is prevalent, with cutaneous tropism but potential to affect visceral organs and worsen clinical outcomes. Evaluating infection progression to visceral organs over time is essential for diagnosis, monitoring, control, and therapeutic intervention. To analyze L. amazonensis infection in the skin and liver of C57BL/6 mice over time to better understand disease progression and visceral dissemination. Skin and liver tissues from C57BL/6 mice were collected at 15- and 90-days post-infection with Leishmania amazonensis . Parasite load was quantified by RT-qPCR targeting the 18S ribosomal gene region, allowing detection of all Leishmania species, and complemented by histological analysis with hematoxylin and eosin staining. Differences in parasite loads among groups (control, 15- and 90-days post-infection) were statistically analyzed and considered significant when p<0.05. Skin parasite loads were 7,342.34 and 40,886.90 parasites/biopsy at 15 and 90 days, respectively, while liver loads were 8.62 and 18.01. Due to lack of normality and independence among groups, the Kruskal-Wallis test was applied, indicating significant differences in both skin (H=8.649, p=0.0019) and liver (H=8.29, p=0.0035), with n=4/group. Dunn’s post hoc test showed a significant increase in parasite load at 90 days compared with controls in both skin (p=0.0114) and liver (p=0.0156). Histology confirmed cutaneous infection but revealed no significant hepatic alterations. Parasite load increased significantly in skin and liver over time. However, absence of hepatic infection on histology suggests that high values detected may partly reflect circulating parasites within biopsy blood vessels. This highlights the importance of combining histological and molecular methods for more accurate infection assessment.