Re-examining the drivers of variation in parasite loads across hosts in the Tallis-Leyton model.

The Tallis-Leyton model is a simple model of parasite acquisition where parasites accumulate in the host without affecting the host's mortality, or eliciting any immune reaction from the host. Furthermore, the parasites do not reproduce in the host. We examine how the variability in parasite loads among hosts is affected by the rate of infectious contacts, the distribution of parasite entering the host during infectious contacts, the host's age, and the distribution of parasite lifetimes. Motivated by empirical studies in parasitology, variability is examined in the sense of the Lorenz order and related metrics. Perhaps counterintuitively, increased variability in the distribution of parasite lifetimes is seen to decrease variability in the parasite loads among hosts.