Final answer:
The most virulent subtype of the influenza virus is Influenza A.
Step-by-step explanation:
The most virulent subtype of the influenza virus is Influenza A. Influenza A viruses are known to cause the seasonal pandemics of influenza each year and are associated with more severe disease symptoms. Influenza A can also infect a variety of animals, including pigs, horses, and whales.