Animal viruses can be more deadly than their human
A lot of people have been commenting about the apparent overreaction of governments to the swine flu. Why go to such extreme measures to deal with simple influenza? The reason has to do with the flu pandemic of 1918-1919.
Over those two years, at least three waves of flu struck killing over 600,000 people in the U.S. and a staggering 30-50 million people worldwide. People died at such a high rate that cities ran out of caskets and dead bodies were stacked on porches and in the streets.
Governments have been concerned that history might repeat itself because the two flues share one thing in common--they both started out as animal viruses. And our bodies are not particularly good at fighting off viruses new to humans.
Each year a new flock of flu strains kicks off the flu season. Almost always these strains are variations of human flues from previous years. What this means is that we have seen cousins of these viruses in the past and so have a leg up on mounting an attack and defeating them.
We do not have this same leg up on animal viruses. Our immune systems haven't seen anything like them and so can't mount a quick attack. The end result is that the percentage of people who die from animal flues tends to be much higher than from run of the mill human flues.