This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Communicable diseases, Subject name: Social & Preventive Medicine
Swine flu is caused most commonly by- 
Select and explain. 
A. H1N1, B. H5N1, C. H3N2, D. B virus
A: H1N1
Answer: A: H1N1 
Explanation: (ref: park's text book 23rd edition) Swine flu is caused by the pandemic influenza virus( H1N1) Its incubation period varies from 2-3 days It differs in its pathogenicity from seasonal influenza in 2 ways: - majority of human population has little or no immunity against it,the impact of infection has been in a wider range. -virus can infect lower respiratory tract and cause rapidly progressive pneumonia,especially in children and young to middle aged adults. .