An organism that carries a disease-producing organism or parasite is known as a what?

• A. Parasite
• B. Pathogen
• C. Reservoir
• D. Vector

Answer: (D)

In disease transmission, the organism that carries a disease-producing agent and passes it to others is a vector. A vector acts as a bridge, often spreading the pathogen when it bites or contacts a new host, enabling the disease to move through a population. For example, mosquitoes are vectors for malaria because they carry the Plasmodium parasite and transmit it to people when they bite.

A parasite, by contrast, is the organism that lives on or in another organism and benefits at its expense, not specifically the carrier that spreads disease. A pathogen is the disease-causing agent itself (the bacterium, virus, or protozoan), not the carrier that transmits it. A reservoir is an organism or environment that harbors the pathogen over time, maintaining it, but isn’t necessarily the direct vehicle that transmits it to new hosts.