How the 1918 strain of Swine Flu is related to all flu pandemics
The 1918 Pandemic began with both people and pigs coming down with the flu at the same time. Before then, flu-like illnesses in pigs had not been reported, making scientists think it was passed from human to animal and not the other way around. It lasted from march of 1918, to June of 1920, and killed over one billion people world wide. Over one third of the entire population was infected, with over 28% of the fatalities coming from North America. Few countries were able to prevent any deaths and only then by imposing severe restrictions on trade and travel for months, which hurt them economically.
How the 1918 Swine Flu is related to all Pandemics
Pigs are one of few animals capable of carrying multiple strains of influenza, making them a hatchery for new, more lethal forms. They can carry swine, human, and avian flu,(bird) and mix them, then transmit the new version to people through coughing, sneezing, mucus and other forms, including breathing. As a result, all forms of flu now carry markers from the 1918 pandemic, as current strains have been bred in pigs, which have carried and circulated the 1918 form continuously since then.
Another way to put this, is to think of crossbreeding plants. The DNA strains of the first ones can be found in the new versions. Even crossbreeds ten generations later will still bear the markers of the original and will not only be influenced by them, but keep passing the DNA down. Swine flu works the same way and as it mutates,(drifts) it keeps the 1918 strain from dying out. As long as there are pigs, the 1918 Swine Flu will continue to be a part of new swine strains and will always be the 'Mother' of all Swine Flu, since it did not exist before then in pigs.
Therefore, all current and future Pandemics of Swine Flu are related to the 1918 strain, due to human interaction with pigs, who make perfect hosts for not only human and swine flu but also for avian. 2009-10 H1N1, is a mix of all three and a proven descendant of the 1918 Pandemic. Scientists are still studying exhumed tissue to discover the exact causes and first cases of the 1918 Pandemic.
Sources:
news/statements/2009/h1n1_pandemic_phase6_20090611/e n/index.html
http://en.wikipedia.org/wiki/Swine_influenza
http://www.sciencedaily.com/releases/2009/04/0904301 11640.htm