How changes in biodiversity affect disease, particularly in the face of large-scale land-use change, is a contentious topic in disease ecology that has implications for public health and conservation policy. The ‘dilution effect’ hypothesis argues that declines in biodiversity are associated with increased disease risk, but this can be challenging to demonstrate because many pathogens have complex life cycles such that changes to the species composition and abundance of hosts can influence the density and infection prevalence of vectors via multiple mechanisms. Key to addressing this debate is a quantification of interactions between hosts, vectors, and pathogens. In their recent study published in Molecular Ecology, Kocher et al. (2022) captured thousands of sandflies, some species of which are vectors for the Leishmania protozoan that causes Leishmaniasis, across a human footprint gradient in French Guiana (Fig. 1). By implementing DNA metabarcoding of vectors combined with an innovative modeling approach, they effectively quantified the nuanced relationships between changes in land-use, mammalian host diversity, vector abundance, and parasite prevalence. In support of the dilution effect hypothesis, Kocher et al. found that sites with higher mammal diversity were associated with lower relative abundance of reservoir hosts and higher Leishmania infection prevalence in sandflies. However, while infection prevalence was lower when mammal diversity was high, the density of sandfly vectors was higher, which resulted in a weak overall effect of mammal diversity on the density of infected vectors, the most important indicator of Leishmania transmission risk.