An organism that spreads disease without directly causing it?

• A. A bacterium
• B. A virus
• C. A prion
• D. A vector

Answer: (D)

A vector is an organism that transmits pathogens from one host to another without being the disease-causing agent itself. The main idea here is that the organism facilitates spread, not the illness itself. For example, mosquitoes can carry malaria parasites or viruses like dengue between people, enabling infection while the mosquito isn’t causing the disease directly. In contrast, bacteria, viruses, and prions are pathogens that can cause disease themselves, rather than primarily serving as carriers between hosts. Some vectors are biological, with the pathogen multiplying inside the vector, while others are mechanical, simply carrying the pathogen on their bodies.