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 PCR and qPCR to identify infected individuals, and MinION sequencing to determine the Plasmodium species involved, 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, infected chimpanzees were younger than non-infected individuals, although no significant association was detected between age and parasitemia levels, and this interpretation should be considered cautiously given the limited number of juvenile animals included in the study. Multi-species infections, particularly triple infections involving P. vivax-like parasites, were associated with higher parasitemia levels. 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-1β, 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 highlights 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.