Swine influenza is flu virus usually found in pigs. The virus occasionally changes (mutates) and becomes infectious in humans. When this happens, the disease becomes a concern to humans, who have little or no immunity against it. This means the virus has the potential to spread quickly around the world. It also may be more difficult to treat than the usual, seasonal human flu viruses.

Symptoms of H1N1 flu infection in humans are similar to classic flu-like symptoms, which might include:

• Fever above 100.4 °F
• Cough
• Sore throat
• Headache
• Chills
• Muscle aches
• Diarrhea
• Vomiting