A tritrophic "prey-intermediate predator-top predator" population system with disease in the intermediate predator is considered. For this 4D-model, the bifurcation analysis is performed. In this analysis, the rate of the disease transmission is used as a bifurcation parameter. A variety of mono-, bi- and tri-stable behaviors with regular and chaotic attractors are analyzed. It is shown how random disturbances of the bifurcation parameter cause multistage stochastic transformations, noise-induced excitement, and stochastic transitions from order to chaos and reversely. These noise-induced effects are studied in terms of stochastic P- and D-bifurcations.