In this paper we consider a three level food web subject to a disease
affecting the bottom prey. The resulting dynamics is much richer with respect
to the purely demographic model, in that it contains more transcritical
bifurcations, gluing together the various equilibria, as well as persistent
limit cycles, which are shown to be absent in the classical case. Finally,
bistability is discovered among some equilibria, leading to situations in which
the computation of their basins of attraction is relevant for the system
outcome in terms of its biological implications
