This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: VBDs, Arboviral & Viral Infections, Surface Infections, Subject name: Social & Preventive Medicine
[{'content': 'Which of the following dengue sequential serotypes infection are associated with maximum risk of dengue hemmorhagic fever? \nSelect and explain. \nA. DENV-1/DENV-2, B. DENV3/DENV-2, C. DENV-4/DEN-V2, D. Similar risk with all', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Studies in Thailand have revealed that the DENV-1/ DENV-2 sequence of infection was associated with a 500 fold risk of DHF compared with primary infection. For the DENV-3/DENV-2 sequence the risk was 150-fold, and a DENV-4/DENV-2 sequence had a 50-fold risk of DHF. There is no time-limit to sensitization after a primary infection. The 1997 Santiago de Cuba epidemic clearly demonstrated that with the introduction of DENV-2, DHF had occurred 16-20 years after the primary infection with DENV-1.', 'role': 'assistant'}]