Exacerbated Hepatic, Splenic, and Neuropathology in BALB/c Mice Co-Infected with <i>Leishmania </i><i>m</i><i>ajor</i> and <i>Plasmodium </i><i>b</i><i>erghei</i>

Co-infection with multiple protozoan parasites is a frequent yet understudied phenomenon. Leishmania major and Plasmodium berghei evoke distinct immune responses that may interact during co-infection to alter disease progression. This study aimed to evaluate the histopathological implications in BALB/c mice concurrently infected with L. major and P. berghei. One hundred sixty BALB/c mice were assigned to four groups: naïve, L. major-only, P. berghei-only, and co-infected. Body weight, parasitemia, parasite burden, and complete blood count (CBC) were monitored. Spleen and brain tissues were harvested, fixed, and examined histologically. Comparative assessments were made against naïve controls. Histopathological evaluation of BALB/c mice revealed that co-infection with Leishmania major and Plasmodium berghei induced more severe and widespread organ damage than single infections with either parasite. In the liver, co-infected mice exhibited extensive granuloma formation, diffuse infiltration of immune cells, hepatocyte degeneration, and vascular congestion. Splenic sections showed complete loss of red/white pulp boundaries, massive lymphoid follicle hypertrophy, dense leukocytic infiltration, abundant megakaryocytes, fibrosis, and pronounced hemozoin deposition. Brain tissue analysis demonstrated severe blood-brain barrier disruption, widespread hemorrhage, intense microgliosis, granuloma formation, and marked neuronal degeneration. Notably, certain neuroinflammatory and systemic pathological features—particularly extensive CNS involvement in L. major infection—have not been previously reported. These findings highlight the synergistic exacerbation of tissue injury in co-infection and underscore the need for integrated control strategies in regions where leishmaniasis and malaria are co-endemic. The findings demonstrate that co-infection with L. major and P. berghei leads to exacerbated disease manifestations and altered immune homeostasis.