This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
[{'content': 'A four-fold increase in the titre obtained in Weil Felix reaction is diagnostic of - \nSelect and explain. \nA. Rickettsial infection, B. Fungal infection, C. Spirochetal infection, D. Viral infection', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]