Packer, Holt, Hudson, Lafferty, Dobson Craig, Robert D., Peter J., Kevin D., Andrew P. Keeping the herds healthy and alert: implications of predator control for infectious disease. 2003 Ecology Letters 6:797-802. Excerpts from the Abstract:
...predator removal could prove harmful to prey populations that are regulated primarily by parasitic infections rather than by predation.
In general, predator removal is more likely to be harmful when the parasite is highly virulent, macroparasites are highly aggregated in their prey, hosts are long-lived and the predators select infected prey.