Which term describes a disease type that increases the likelihood of spread within a herd?

• A. Transmissible (or contagious).
• B. Non-transmissible.
• C. Environmental-only disease.
• D. Genetically resistant herd.

Answer: (A)

Transmissible disease describes a condition that readily passes from one animal to another, so it increases the likelihood of spread within a herd. Pathogens can move through direct contact, aerosols, shared water or feed, contaminated equipment, or vectors, enabling multiple herd members to become infected. The closer the contact and the more efficient the transmission route, the higher the spread, often reflected by a basic reproduction number above 1. Non-transmissible diseases don’t spread easily between animals, environmental-only diseases rely on environmental exposure rather than direct animal-to-animal transmission, and a genetically resistant herd reduces transmission by limiting susceptible hosts.