It really depends on what the operational definition of "deadly" is to you. Carnivorous dinosaurs certainly could have been more than capable of tearing a person to shreds. Other animals can sting you with poison that can kill you quickly or cause you to have a slow agonizing death. An insect carrying a deadly virus could hypothetically cause a pandemic. It is speculated that historically rats helped to spread plagues throughout Europe around the 14th century which resulted in millions of deaths.