Hidden hematological, biochemical and immune costs of asymptomatic malaria infections in semi-wild chimpanzees

The health consequences of Plasmodium infections in wild great apes, particularly in asymptomatic animals, remain poorly understood. This study investigated the hematological and immune impacts of natural malaria infections in 27 semi-wild chimpanzees (Pan troglodytes troglodytes) from Gabon. Using MinION sequencing and species-specific PCR, results showed a 48.15% overall Plasmodium infection rate, with frequent multi-species co-infections involving Plasmodium gaboni, Plasmodium reichenowi, and Plasmodium vivax-like parasites. In addition, younger animals were significantly more infected and exhibited higher parasitemia levels, especially those with triple infections involving P. vivax-like. Profiling of 15 hematological markers and 8 cytokines/chemokines known to be associated with malarial infections in humans revealed significant alterations in infected chimpanzees, including elevated urea, reduced creatinine, and increased systemic concentrations of pro-inflammatory (TNF, IL-1{beta}, CCL3) and anti-inflammatory (IL-10) cytokines. Ex vivo PBMC stimulation yielded higher IL-10 in infected than non-infected individuals, indicating a regulatory-skewed cytokine response at the time of sampling. These results suggest that malaria in chimpanzees is associated with systemic immune modulation and accompanied by signs of physiological stress, including potential renal dysfunction. This study challenges the assumption that chronic Plasmodium infections are entirely benign in great apes and highlight the need to integrate immunological health indicators into conservation strategies. Broader immune profiling and longitudinal studies will be essential in the future to assess long-term health outcomes and resilience in these endangered populations.