Swine flu, bird flu, Spanish flu, Asian flu, and most other named flu epidemics are caused by the influenza A virus. Both influenza A and influenza B cause seasonal epidemics, but the A type has additional potential to cause global pandemics.
Dr. Conall McCaughey of Royal Hospitals, Belfast, UK, provided a review. The names H1N1, H3N2, etc. refer to subtypes characterized by their surface proteins hemagglutinin (H) and neuraminidase (N).
McCaughey listed eight recorded major outbreaks caused by influenza A:
1. In 1889, H2N2 pandemic, estimated deaths of 1 million.
2. In 1900, H3N2 pandemic, estimated deaths of < 1 million.
3. In 1918, H1N1 “Spanish” flu pandemic, estimated deaths 20 to 100 million.
4. In 1957, H2N2 “Asian” flu pandemic, estimated deaths 1 to 1.5 million.
5. In 1968, H3N2 “Hong Kong” flu pandemic, estimated deaths 0.75 to 1 million...
6. In 1977, H1N1 “Russian” flu, not a true pandemic, estimated deaths < 100,000.
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