An organism that transmits pathogens is called a

Step 1: Analyze the question The question asks for the term used for an organism that carries and passes on disease-causing agents (pathogens) from one host to another.

Step 2: Explain the concept A vector is an organism, usually an animal or insect, that carries a pathogen from one host to another. The vector often does not get sick itself, or it may be only a carrier. Some common examples:

• Female Anopheles mosquito → transmits Plasmodium (malaria)
• Tsetse fly → transmits Trypanosoma (sleeping sickness)
• Aedes mosquito → yellow fever and dengue
• Housefly → typhoid, cholera and dysentery (mechanical vector)
• Rat flea → plague

Step 3: Check each option

• A. Prey: an animal that is hunted and eaten by a predator. This has nothing to do with disease transmission.
• B. Commensal: an organism that benefits from a relationship while the other partner is neither helped nor harmed.
• C. Parasite: an organism that lives on or in a host and harms it. A parasite can be the pathogen itself, but the term does not mean the carrier that transmits it. This is the most tempting wrong option.
• D. Symbiont: an organism living in a close association with another, usually to mutual benefit.
• E. Vector: an organism that transmits pathogens. This matches the definition.

Step 4: Answer The correct option is **E.

Exam tip: Think "Vector = Vehicle." A vector is the vehicle that carries the germ from one host to another. Don't confuse it with the parasite, which is the germ or organism doing the harm. For example, in malaria the Plasmodium is the parasite and the female Anopheles mosquito is the vector.