Which of the following are determinants of the agent that causes disease?

• A. Host age and breed
• B. Environmental temperature only
• C. Vaccination status of the host
• D. Pathogenicity, virulence, strains, genetic variability

Answer: (D)

Determinants of the agent are the inherent properties of the infectious organism that influence whether exposure leads to disease and how severe it might be. Pathogenicity describes the organism’s overall ability to cause disease. Virulence refers to how severe the disease can be once infection occurs. Differences among strains can mean some are more capable of causing disease or more aggressive than others. Genetic variability can alter these traits, affecting how the agent interacts with the host, its range, and its evasion of defenses. These factors are intrinsic to the agent itself, not to the host or the environment. In contrast, host age and breed influence susceptibility, vaccination status shapes host immunity, and environmental temperature affects survival or exposure opportunities but does not change the agent’s own disease-causing properties. Hence, the determinants of the agent include pathogenicity, virulence, strains, and genetic variability.