types of microorganisms that cause infection include
Credit: Dr. Libero Ajello/CDC. In addition to viruses and bacteria, there are three other major types of microbes that can cause infectious diseaseâand one newly discovered type. As with viruses and bacteria, not all of the species in each of these categories are infectious to humans. But many of the worldâs most prevalent infectious diseases are caused by microbes that are included in the groupings below. Fungi cause a wide variety of diseases in humans, ranging from Athleteâs foot to ringworm to deadly histoplasmosis.