What are the two broad types of disease agent transmission?

• A. Horizontal (direct and indirect) and vertical
• B. Horizontal transmission only
• C. Vertical transmission only
• D. Direct contact and vector-borne transmission

Answer: (A)

The main idea is that disease transmission falls into two broad categories: horizontal transmission, which occurs within a generation, and vertical transmission, from parent to offspring. Horizontal transmission can be direct (person-to-person contact) or indirect (through contaminated objects, droplets, aerosols, or vectors). Vertical transmission happens across generations—from mother to child during pregnancy, birth, or breastfeeding. This framing captures all common routes and makes sense of how infections spread over time. The other options only describe specific routes within horizontal or miss one broad type entirely, so they don’t cover the full concept.