This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Epidemiology, Subject name: Social & Preventive Medicine
[{'content': 'Virulence of a biological agent is defind as - \nSelect and explain. \nA. Ability of the agent to invade and multiply in host, B. Propoion of clinical cases resulting in severe clinical manifestation, C. Ability of the agent to induce a clinically apparent illness, D. Propoion of clinical cases in a virgin population', 'role': 'user'}, {'content': "Answer: B \nExplanation: For an infectious agent, infectivity refers to the propoion of exposed persons who become infected. Pathogenicity refers to the propoion of infected individuals who develop clinically apparent disease. Virulence refers to the propoion of clinically apparent cases that are severe or fatal. Ref: 25th edition, Park's Textbook of Preventive and Social Medicine, Page no. 43", 'role': 'assistant'}]