Effects of Vector Density on Blood Parasite Spread and Health Consequences for Avian Hosts: An Experimental Epidemiology Blueprint

Vector density plays a critical role in the transmission dynamics of vector-borne diseases and thus in their health and evolutionary effects. Despite extensive research on pathogens, controlled experimental studies on vector density effects remain limited. This study investigates the relationship between vector density and transmission using the model system of feral pigeon Columba livia, hippoboscid fly Pseudolynchia canariensis, and the haemosporidian blood parasite Haemoproteus columbae. Five experimental groups of pigeons were exposed to increasing numbers of infected louse flies (0-4 per bird) to quantify the resulting infection prevalence, transmission speed, and effects on host health and behavior. Over 50 days, infection prevalence correlated positively with vector density. Higher vector exposure linearly accelerated infection onset and increased prevalence. By day 80, all groups had reached 100% infection. With increasing vector densities, breathing rate decreased. Body temperature slightly increased in infected birds over time. These findings demonstrate the importance of vector density in shaping disease transmission and show how low vector densities limit parasite spread. The transmission power laws in similar systems may strongly depend on the morphology and life-history peculiarities of vector taxa. The pigeon-louse fly system offers a comfortable model system for experimental research on vector-borne disease ecology. The current study presents an experimental epidemiology template for quantifying the role of vector numbers and behavior in shaping transmission dynamics, parasite population structure, host-parasite co-evolution, and its health consequences.