An infectious disease is caused by

An infectious disease is caused by

• A. Pathogens such as viruses, bacteria, parasites, and fungi.
• B. Environmental toxins.
• C. Genetic mutations only.
• D. Nutritional deficiencies.

Answer: (A)

Infectious diseases are caused by pathogens—biological agents that invade a host and can be transmitted to others. These pathogens include viruses, bacteria, parasites, and fungi, all of which can multiply within the body and spread between people or through the environment. This distinguishes infectious diseases from conditions caused by non-biological factors: environmental toxins cause disease through chemical injury, genetic mutations alter cellular function to produce disease, and nutritional deficiencies result from a lack of essential nutrients. So the presence and activity of a transmitting biological agent is what defines an infectious disease.

Infectious diseases are caused by pathogens—biological agents that invade a host and can be transmitted to others. These pathogens include viruses, bacteria, parasites, and fungi, all of which can multiply within the body and spread between people or through the environment. This distinguishes infectious diseases from conditions caused by non-biological factors: environmental toxins cause disease through chemical injury, genetic mutations alter cellular function to produce disease, and nutritional deficiencies result from a lack of essential nutrients. So the presence and activity of a transmitting biological agent is what defines an infectious disease.