What is a main factor for determining the number animals used as sentinels?

• A. The space available in the animal room
• B. The cost involved in maintaining the animals
• C. The number of pathogens being tested
• D. The expected morbidity of the agents being monitored

Answer: (D)

The key idea is how easily an infection would be detected in sentinels. If the agents being monitored are expected to cause illness (high morbidity) or produce clear, observable effects, you can detect their presence with fewer sentinel animals because infections are more readily marked by signs or mortality. If the agents have low morbidity or are subclinical, infections may go unnoticed unless you have more sentinels or use highly sensitive testing, so more animals are needed to achieve reliable detection. Therefore, the expected morbidity of the agents being monitored mostly determines how many sentinels you should use. Operational factors like space, cost, or how many pathogens are tested influence feasibility but don’t directly set the detectability in the same way as morbidity does.