Pathogen

A pathogen is any organism or agent capable of causing disease in its host. Pathogens are highly diverse and include bacteria, viruses, fungi, protozoa, parasites (such as worms), and even infectious proteins known as prions. While the human body contains a vast array of microbes—most of which are harmless or beneficial—pathogens specifically possess mechanisms that allow them to invade hosts, evade immune responses, and cause infection or disease. Pathogenicity refers to an organism’s ability to cause disease. Virulence describes how severe that disease is. These properties depend on factors such as infectivity, transmission mode, and production of virulence factors.

Other names

Infectious agentMicrobeDisease-causing organism

Varies depending on the pathogen and drug; examples include inhibition of cell wall synthesis, disruption of viral replication, and interference with metabolic pathways.