ALLOMETRY AND SIMPLE EPIDEMIC MODELS FOR MICROPARASITES

SIMPLE mathematical models for microparasites offer a useful way to ex amine the population dynamics of different viral and bacterial pathoge ns, One constraint in applying these models in free-living host popula tions is the paucity of data with which to estimate transmission rates . Here we recast a standard epidemiological model by setting the birth and death rates of the host population and its density as simple allo metric functions of host body weight. We then use standard threshold t heorems for the model in order to estimate the minimum rate of transmi ssion for the parasite to establish itself in a mammalian host populat ion, Transmission rates that produce different comparable values of th e parasites' basic reproductive number, R(o), are themselves allometri c functions of host body size. We have extended the model to show that hosts having different body sizes suffer epidemic outbreaks whose fre quency scales,vith body size. The expected epidemic periods for pathog ens in different mammalian populations correspond to cycles observed i n free-living populations.