Final answer:
The primary reservoir species for influenza A are birds, with wild waterfowl being the most significant carriers. Avian species can carry and spread influenza A viruses without falling ill, and certain subtypes, such as H1N1 and H5N1, have caused serious human outbreaks.
Step-by-step explanation:
Influenza A Reservoir Species
The reservoir species for influenza A virus are birds, particularly wild waterfowl. These avian species frequently harbor the virus without showing symptoms, acting as a natural reservoir from which periodic influenza outbreaks in humans can occur. Influenza A viruses are capable of infecting a variety of animals, including not only birds but also pigs, horses, and marine mammals like whales and dolphins.
Different subtypes of influenza A, defined by their hemagglutinin (H) and neuraminidase (N) proteins, have potential to cause human illness, yet only a few, such as the H1N1 and H5N1, have led to significant human pandemics.
The highly pathogenic avian influenza (HPAI) strain, H5N1, is an example of a deadly strain that has raised concerns over its potential to cause a human pandemic, due to its high mortality rates in humans, though it primarily spreads from infected birds to humans and has not yet evolved to transmit easily between humans.