How many pathogens are there?

The exact number of pathogens is not known as new ones are constantly being discovered. There are millions of different types of microorganisms that occur naturally including bacteria, viruses, fungi, and parasites, and many of these cause disease in humans, animals and plants. The number of recognized pathogenic species is large and includes over 1,400 human pathogens including 217 viruses, 527 types of bacteria, 302 species of fungi and 397 types of parasites.