Among other things in their lode, they've found ticks, nematodes, biting flies and all sorts of other nasties, including intestinal parasites, dating back to the Cretaceous period. From some of the insects, the Poinars have extracted microbes that cause leishmania and malaria — evidently new pathogens back then, against which dinosaurs wouldn't have had much resistance.
The authors aren't arguing that the dinos all died in a massive epidemic; rather, the constant wear and tear of illness weakened the dinosaurs so that other catastrophes, like comets and volcanoes, could have finished them off. Still, the Poinars couldn't resist a bit of made-for-Hollywood drama. One great quote from the book: "The largest of the land animals, the dinosaurs, would have been locked in a life-or-death struggle with [insects] for survival."
