In 1918 –19 the whole world experienced the first known flu pandemic of H1N1 Influenza (Bird Flu). There may have been many influenza outbreaks before that time, but medical science was not advanced enough to have kept track of them.
The 1918 Pandemic was called “Spanish Flu” because the world first became aware that it existed when it swept through Spain. It has been estimated that 40- 70 million (Or more people died (There are some estimates of 100 Million) worldwide from Spanish Flu (Nobody has valid numbers of dead for China, IndoChina, India, Africa and most of Latin America.).
It is commonly believed that American soldiers in World War One actually brought it over to Europe after an initial outbreak in Fort Riley, Kansas. It then also spread to the East Coast of the US where troops were staged prior to being shipped overseas. All we know for certain was that it became a horrible pandemic in Europe towards the end of Word War One and from there it spread all over the world. It may have assisted in bringing the end to the war.
Flu is very infectious, as everybody who ever had it knows, and most of us have had it. With most recent flu infections, the morbidity is not high. Your immune system fights it and eventually you get healthy again. Yet, some strains are stronger than others. The death rate rises, particularly among the elderly and the very young.
When a new strain of virus shows up on the world scene it usually takes a higher toll of victims, simply because your body defenses do not recognize the new virus. The Bird Flu viruses are numbered according to protein molecules (glycoproteins ) on the surface of the virus.
In 1957-58 a new virus with variances in the surface protein structure evolved in Asia and it was called H2N2 “Asian Flu” (The Spanish didn’t get blamed this time!).
In 1968-69 we experienced the last major pandemic from a new strain of bird flu virus that was first reported in the British Hong Kong Colony area. We called it “Hong Kong Flu” to give it some specificity and to differentiate it from “Asian Flu.” This was the H3N2 Strain. Again, the body immunological capacity did not recognize this new strain and many people died. By the way, the “H” comes from hemagglutinin which is the major surface glycoprotein on the virus. The N stands for neuraminidase, another protein on the surface of the virus.
Note, ALL INFLUENZA A VIRUSES ARE BIRD FLU!
All the human flu viruses of recent history have been Hong Kong Flu or a reemergent but far weaker H1(Russian flu) Bird Flu strains. All of the influenza viruses have been carried by birds. Most are carried in other animals, like pigs. It was long thought that the bird viruses passed to pigs where they picked up characteristics from other viruses that were common to both man and pig and were thus able to transfer to man.
When H1N1 first broke out in Fort Riley Kansas, the army base was next to a pig farm. In fact the first person believed to have become ill from “Spanish Flu” was an Army cook who purchased pork from that farm to prepare for the troops at the fort.
H4 never crossed over from bird to man, but a new strain of bird virus has and it has been numbered H5 because it has the fifth variance found on the hemagglutinin. H5N1 has the potential to be as bad or even worse than H1N1 in 1918. To date it has only been seen to jump from a non human source to a human and then to jump three or four times to other humans. It is not a pandemic virus yet, but it only needs a few modifications on its surface proteins to do so.