Sequential Leishmania major and Plasmodium berghei Co-Infection Exacerbates Disease Severity, Parasite Burden and Hematological Alterations in BALB/c Mice

In tropical and subtropical countries, malaria and leishmaniasis are significant vector-borne parasitic infections that can often be present at the same time, posing a risk of concurrent infections. However, their roles in disease progression and host responses are not well understood. In the present study, we investigated the effects of consecutive infection with L. major and P. berghei in BALB/c mice. BALB/c mice were randomly allocated to naïve, L. major mono-infected, P. berghei mono-infected and co-infected groups. We observed body weight, Leishmania parasite burden in the footpad, and hematological parameters over a 13-day follow-up after malaria infection. Co-infected mice developed more severe disease than either mono-infected group, exhibiting greater body weight reduction, with mean body weight declining to 24.8 ± 2.4 g by Day 13, compared with 28.1 ± 1.5 g in L. major-infected mice and 26.9 ± 1.9 g in P. berghei-infected mice. The co-infected mice also had higher parasitemia than P. berghei mono-infected mice (23.73 ± 3.02% vs. 19.63 ± 3.39%; p = 0.008), and higher Leishmania parasite burden than L. major mono-infected mice (34.00 ± 1.38 vs. 28.92 ± 6.16; p = 0.041). Co-infection induced anemia, thrombocytopenia, leukocytosis, neutrophilia, lymphopenia and monocytosis. These findings show that co-infection with L. major–P. berghei exacerbates disease severity, boosts the burden of malaria, and worsens hematological dysfunctions; thus, highlighting the need for an integrated approach to malaria–leishmaniasis co-infections in endemic areas.