Skip to main content
Dryad

Variation in pathogen load and the pathogen load–infectiousness relationship broaden avian malaria’s distribution

Seidl, Christa M.1; Parise, Katy L.2; Ipsaro, Isaiah J.1; Leach, Sarah1; Hays, Delson1; Morimoto, Ranger1; Banister, Kelsey2; Ferreria, Francisco C.3; Abraham, Elizabeth4; Foster, Jeffrey T.2; Paxton, Eben H.4; Kilpatrick, A. Marm1

Published Jan 08, 2026 on Dryad. https://doi.org/10.5061/dryad.g1jwstr24

Data files

Abstract

The infectiousness of host species and the feeding patterns of vectors influence pathogen distribution and transmission intensity. Two aspects of host infectiousness shape transmission but are underappreciated: the relationship between pathogen load and infectiousness and variability in pathogen load within species. We quantified the relationship between host parasitemia for avian malaria (Plasmodium relictum) and infectiousness for biting Culex quinquefasciatus mosquitoes using experimentally infected birds. We used this relationship and 4,218 samples from wild birds to estimate the relative importance of hosts’ acute and chronic stages of infection, the infectiousness of 17 bird species in Hawaiʻi, and mosquito feeding preferences. Infectiousness to mosquitoes increased with host parasitemia (and temperature and time since feeding), but the relationship’s gradual slope led to a wide range of parasitemias being partly infectious to mosquitoes. Chronic stage infections create far more infectious mosquitoes than the acute stage, and high within-species variability in parasitemia led to broad overlap in the infectiousness of most bird species. Disproportionate feeding patterns (inferred from relative infection prevalence) elevated the importance of a few bird species in transmission, but broad overlap in species infectiousness resulted in most host communities having similar total infectiousness. Similar community infectiousness helped explain the widespread distribution of avian malaria throughout Hawaiʻi despite highly variable species communities - it was detected at 63/64 moderately well-sampled sites. These results demonstrate the importance of the shape of the pathogen load-infectiousness relationship and within-species variability in pathogen load in influencing a pathogen’s host range, transmission intensity, and spatial distribution.