H1N1 swine flu caused the 1918 flu pandemic: the same type (A) and strain (H1N1) behind the current crisis, but a different branch or "clade." Classical H1N1 viruses were "virtually the exclusive cause" of swine flu in the U.S. and Canada from 1930 (when they were first isolated) to 1998. Then things changed.

A new H5N1 bird flu mutation with a 91% fatality rate in humans appeared this month: between March 1 and March 24 of 2006, the WHO reported 12 new H5N1 cases with 11 deaths. By comparison, H5N1’s fatality rate was 50% in 2004 and 2005 with a total of 131 new cases and 66 deaths. The new virulently fatal Asian H5N1 mutation creates a second genetic track for H5N1 to spread easily from human-to-human. It is spreading through Asia, Europe and Africa and is expected to enter North America with migratory birds, if not on consumer goods or with travellers. The mainstream media is focusing on studies that show humans are resistant to airborne H5N1. Few acknowledge that the H5N1 virus is shed in bodily fluids and spreads mainly via wastewater into waterways, and on physical contact. The virus can live for months on cold surfaces and up to 200 days in water; it infects fish, and animals that drink contaminated water. Unlike most flus, H5N1 can enter the human body through the gut as well as the respiratory system - via contaminated water and infected meat.