Forgotten reservoirs: an attempt to revive field research on rodent malaria parasites in their main natural host, the thicket rat Grammomys poensis (formerly Thamnomys rutilans)

Abstract

<title>Abstract</title> Rodent malaria parasites have long served as essential experimental models for understanding human malaria, yet little is known about their ecology and evolution in the wild. The thicket rat <italic>Grammomys poensis</italic> (formerly <italic>Thamnomys rutilans</italic> ) is considered the main natural host of murine <italic>Plasmodium</italic> species in Central Africa. This study aimed to establish a long-term field site to investigate <italic>Plasmodium-Grammomys</italic> interactions under natural conditions in southeastern Gabon. Over a period of 18 months, trapping was conducted across twelve forest fragments in the Batéké Plateau region using both Tomahauk traps and direct collection at nest. Despite an intensive effort (12,150 trap-nights and 1380 nests inspected), only 20 adult <italic>Grammomys</italic> were captured, all by collection directly at nest, and none were infected with <italic>Plasmodium</italic> as determined by two sensitive nested-PCR assays targeting the <italic>cytb</italic> gene, suggesting extremely low transmission or absence of parasite circulation in the study system. These results contrast with earlier studies reporting high infection prevalence in <italic>Grammomys</italic> from other Central African regions. The absence of infection may reflect local extinction of <italic>Plasmodium</italic> lineages, limited vector exposure due to the absence of species feeding on arboreal rodents, or host resistance. Because the rodent malaria lines currently used as experimental models in laboratories worldwide were isolated decades ago and have since been maintained through serial passage, access to recent field isolates would be highly valuable for capturing contemporary natural diversity and for enhancing the ecological, evolutionary, and biomedical relevance of these model systems. This study highlights both the challenges of studying this host-parasite system in the wild and the possibility that rodent <italic>Plasmodium</italic> transmission in this system may be more spatially and ecologically constrained than previously assumed.