What is the term for an organism capable of causing a disease?

The term for an organism capable of causing a disease is "pathogen." Pathogens include a wide variety of microorganisms such as bacteria, viruses, fungi, and parasites that can invade a host organism and provoke an immune response, often resulting in illness or disease. The capability of a pathogen to cause disease depends on various factors, including its virulence, the host's immune response, and the environment in which the interaction occurs. Understanding pathogens is crucial in fields such as medicine, ecology, and environmental science as it helps in disease prevention and management strategies.

The other terms relate to biological interactions but have different meanings. For instance, symbionts are organisms that live in close association with another organism, which may be mutualistic, commensalistic, or parasitic in nature, but not all symbionts cause disease. Parasites are a type of pathogen that specifically lives on or in a host and draws nutrients at the host's expense; however, not all parasites cause diseases in the way pathogens do. Vectors are organisms that transmit pathogens from one host to another, such as mosquitoes transmitting malaria, but they do not directly cause the disease themselves. Thus, "pathogen" specifically refers to those organisms that can initiate disease processes