A Generalized Model of Parasitoid, Venereal, and Vector-Based Transmission Processes

TLDR

General models that incorporate search behaviors demonstrate that attack rates in host‑parasitoid systems parallel transmission processes in sexually and vector‑transmitted diseases, with density‑dependent transmission depending on infective density and frequency‑dependent transmission depending on the proportion of infectives. The study aims to develop unified, general transmission models to enable comparison across systems and to investigate the evolution of transmission dynamics. The authors show that transmission processes span the extremes of a Type II functional response, with vector‑based transmission probabilities ranging from density‑dependent to proportional to I/N², and that limited host visits per vector can cause transmission to decline as host density rises, as observed in pollinator‑transmitted disease data.

Abstract

General models incorporating search behaviors are used to demonstrate the parallels between attack rates in host-parasitoid systems and transmission processes in sexually and vector-transmitted diseases. Density-dependent transmission, in which the probability of an individual's becoming infected is a function of the density of infectives, I, is the usual assumption in disease models. Frequency-dependent transmission, in which the probability of an individual's becoming infected is a function of the proportion of infectives, I/N, is often considered characteristic of venereal and vector-based systems. These two characterizations of the transmission process are shown to represent extremes of the Type II functional response curve. When there is vector-based transmission, and depending on the details of vector behavior, the probability of an uninfected host's becoming infected may range from being predominantly a function of I to being proportional to I/N2. With a limited number of hosts visited per vector, transmission may decline with increasing overall density of the host population; this was observed in empirical data for a pollinator-transmitted disease. Unified, general models of the transmission process are essential for comparison of dynamic processes in different systems and for studies of the evolution of the transmission process itself.