Which of the following is an example of a vehicle in disease transmission?

• A. A doorknob
• B. A tick
• C. A cigarette butt
• D. A water bottle cap

Answer: (A)

In disease transmission, a vehicle is an inanimate object or substance that carries infectious agents from one person to another. A doorknob fits this idea well because it is touched by many people; pathogens can be left on its surface and then picked up by the next person who handles it and touches their mouth, nose, or eyes, facilitating transmission. This makes it a classic example of a vehicle or fomite.

A tick, by contrast, is a vector—an living organism that transmits pathogens during its life cycle. A cigarette butt is not a common or reliable example of a vehicle in epidemiology, and while it could theoretically harbor microbes, it’s not the standard teaching example. A water bottle cap could be considered a vehicle in some contexts, but the doorknob is the prototypical everyday object that clearly demonstrates vehicle transmission through casual contact.