  Many emerging pathogens infect multiple host species, and multi-host
pathogens may have very different dynamics in different host species. This
research addresses how pathogen replication rates and Immune System (IS)
response times are constrained by host body size. An Ordinary Differential
Equation (ODE) model is used to show that pathogen replication rates decline
with host body size but IS response rates remain invariant with body size. An
Agent-Based Model (ABM) is used to investigate two models of IS architecture
that could explain scale invariance of IS response rates. A stage structured
hybrid model is proposed that strikes a balance between the detailed
representation of an ABM and computational tractability of an ODE, by using
them in the initial and latter stages of an infection, respectively.
