What is the term for a microorganism that can cause disease?

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

Answer: (A)

Pathogen is the term for a microorganism that can cause disease in a person. This includes bacteria, viruses, fungi, and parasites. Not every microbe causes illness; many are harmless or helpful. A pathogen can invade tissues, produce toxins, or disrupt normal body functions to create disease symptoms. An antigen is a substance that the immune system recognizes as foreign and mounts a response against; the antigen is not the disease-causing organism itself. A vector is an organism that transmits a pathogen to a new host, such as a mosquito carrying a parasite or virus, but the vector is not the disease-causing organism. A reservoir is a place or organism where a pathogen can live and multiply between transmissions, not necessarily the disease-causing agent itself. Thus, the best term for a microorganism that can cause disease is pathogen.