What causes infectious diseases?

• A. Hormones
• B. Diet
• C. Genetics
• D. Microorganisms

Answer: (D)

Infectious diseases are caused by microorganisms such as bacteria, viruses, fungi, and parasites that invade the body and multiply, producing illness. These agents are the direct culprits behind infection, which is why the disease occurs when a pathogen enters and replicates in our tissues, triggering symptoms and an immune response. For example, a virus like influenza causes illness because it infects respiratory cells, a bacterium like Streptococcus can cause strep throat, a fungus like Candida can lead to candidiasis, and a malaria parasite infects red blood cells.

Hormones, diet, and genetics can influence how we respond to infections or how severe they are, or how easily we become infected, but they are not the actual cause of infectious diseases. Hormonal changes can alter immune function, nutritional status can affect immune resilience, and genetic factors can shape susceptibility, yet the root cause remains the presence and activity of microorganisms.