Oil palm expansion reshapes Culicoides assemblages and avian haemosporidian infections

Land-use change can influence parasite transmission by reshaping ecological interactions among parasites, vectors, and hosts. In particular, deforestation and agricultural expansion modify habitat structure and resource availability, potentially altering the prevalence and distribution of vector-borne diseases.

Fieldwork was conducted on São Tomé Island (Gulf of Guinea, Central Africa) across a land-use gradient from the core of an oil palm plantation to adjacent native forest. Culicoides biting midges and birds were sampled across four habitat types (village, oil palm plantation, at the border between the plantation and the forest, and forested areas) using Centers for Disease Control (CDC) traps and mist nets, respectively. DNA extracted from Culicoides and bird blood was used to screen for Plasmodium, Haemoproteus, and Leucocytozoon using nested polymerase chain reaction (PCR). Blood-fed Culicoides collected in the traps were analyzed by PCR to identify the host species. Linear models were used to assess differences in vector diversity, abundance, host-feeding preferences, and haemosporidian prevalence among habitats.

Culicoides species richness did not differ significantly between habitats, but species abundances did vary. Overall abundance was lower in the oil palm plantation than in border and forest areas. Mammophilic Culicoides were more abundant in the village, whereas ornithophilic species were predominated in the forest. We screened 432 bird blood samples and 452 parous Culicoides for haemosporidian infections. Haemosporidian parasites were most frequently detected in Culicoides pools from the border area. Among birds, Plasmodium prevalence was significantly higher in the oil palm plantation than in border and forest habitats, while Leucocytozoon infections were completely absent in plantation birds.

Anthropogenic habitat disturbance modifies vector communities and host-parasite associations, influencing the transmission dynamics of Haemoproteus parasites. These findings highlight the ecological consequences of agricultural expansion and the importance of preserving natural habitats to mitigate disease emergence under land-use change scenarios.