Which term describes the ability of an agent to cause disease?

The term that best describes the ability of an agent to cause disease is pathogenicity. Pathogenicity specifically refers to the capacity of an organism, such as a virus or bacteria, to produce disease in a host organism by overcoming its defenses and producing a clinical effect. This includes the mechanisms the agent employs to invade the host, multiply, and ultimately result in disease symptoms.

Understanding pathogenicity is crucial in epidemiology as it helps in determining how different agents affect human health and contribute to disease outbreaks. It encompasses the overall impact of the pathogen on the host, which can vary widely among different organisms and strains.

While other terms like infectivity and virulence are related concepts, they address different aspects. Infectivity refers to the ability of a pathogen to enter, survive, and multiply in a host, while virulence indicates the severity of disease that a pathogen can cause once infection occurs. Immunogenicity, on the other hand, is about the ability of an agent to provoke an immune response, which doesn't directly measure the capacity to cause disease. Thus, pathogenicity is the most appropriate choice for defining the ability of an agent to cause disease.