What primarily determines the effectiveness of a biological agent?

• A. Ability of the organism to overcome resistance of the target host.
• B. Method of application of the agent with regard to wind direction.
• C. Type of organism.
• D. Average temperature.

Answer: (A)

Effectiveness hinges on the agent’s ability to overcome the host’s defenses. If the target host has resistance, the biological agent must bypass or suppress those defenses to establish infection or cause its intended effect. When it can overcome this resistance, it can succeed despite host barriers, making the intervention work. While factors like how the agent is delivered, the organism’s inherent characteristics, or ambient temperature can influence outcomes, they modify the chances of success rather than determine it on their own.