  Despite the enormous relevance of zoonotic infections to world- wide public
health, and despite much effort in modeling individual zoonoses, a fundamental
understanding of the disease dynamics and the nature of outbreaks arising in
such systems is still lacking. We introduce a simple stochastic model of
susceptible-infected- recovered dynamics in a coupled animal-human
metapopulation, and solve analytically for several important properties of the
cou- pled outbreaks. At early timescales, we solve for the probability and time
of spillover, and the disease prevalence in the animal population at spillover
as a function of model parameters. At long times, we characterize the
distribution of outbreak sizes and the critical threshold for a large human
outbreak, both of which show a strong dependence on the basic reproduction
number in the animal population. The coupling of animal and human infection
dynamics has several crucial implications, most importantly al- lowing for the
possibility of large human outbreaks even when human-to-human transmission is
subcritical.
