This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Measles, Subject name: Social & Preventive Medicine
[{'content': 'In all of the following diseases chronic carriers are found except: \nSelect and explain. \nA. Measles, B. Typhoid, C. Hepatitis B, D. Gonorrhoea', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' i.e. Measles In measles the only source of infection is a case of measles. Carriers are not known to occur.For more see Q no. 31 of Dec 1998.", 'role': 'assistant'}]