What are the two major modes of transmission?

• A. Horizontal (direct, indirect, airborne) and vertical (in utero and colostrum).
• B. Direct and indirect.
• C. Airborne and droplet.
• D. In utero and colostrum.

Answer: (A)

Two major modes of transmission define how infections spread in a population: horizontal transmission and vertical transmission. Horizontal transmission refers to the spread of pathogens between individuals in the same generation and includes direct person-to-person contact, indirect contact via contaminated objects or environments, and spread through the air (airborne) or by droplets. Vertical transmission, on the other hand, occurs from mother to child, including pathways before birth (in utero) and during early life through breastfeeding (colostrum). The combination described—horizontal with its subtypes (direct, indirect, airborne) and vertical (in utero and colostrum)—covers the broad, widely used framework for classifying transmission routes. The other options isolate only subtypes within a single mode or mix forms that belong to horizontal or vertical, but do not address the two overarching categories together.