For those interested in influenza, the January issue of Emerging Infectious Disease is full or articles about the virus, avian influenza, the chances of a pandemic and much more all written by experts in the field. If you want to learn more about the virus and its disease, this is a must read.
The article by Taubenberger and Morens gives good background and the latest thinking about the 1918 pandemic flu. Some interesting tidbits....
- The H1N1 virus may have had preliminary waves in 1915 and 1917 before the major wave of illness in 1918.
- The H1N1 virus infected pigs and humans simultaneously and both were immnugenetically naive to the virus.
- Viruses that much of the population has not built up an immunity to can strike at any time of year and do not follow the typical pattern of illness in the winter months.
- During 1918 the virus occurred in three waves, spring, summer winter and spring 1919. This rapid reoccurrence was very unusual and is still a puzzle. most influenza viruses take years to antigenicly drift enough to again cause disease, how did the H1N1 virus change so rapidly?
- It is unclear what the source of H1N1 originally was. While the amino acid sequence of the 1918 virus is similar to that of avian strains, its nucleotide sequence is quite divergent. Contemporary avian strains circulating in 1918 are not that much different from today, but are different at the nucleotide from the 1918 H1N1 virus. Did it come from some as yet unknown source?
- The unusual occurrence of high death rates in young people, but not in those over 65 may be explained by those over 65 being exposed to a similar virus in an 1889 outbreak.
I found this comment especially important.
The evolutionary path that led to pandemic emergence in 1918 is entirely unknown, but it appears to be different in many respects from the current situation with H5N1. There are no historical data, either in 1918 or in any other pandemic, for establishing that a pandemic "precursor" virus caused a highly pathogenic outbreak in domestic poultry, and no highly pathogenic avian influenza (HPAI) virus, including H5N1 and a number of others, has ever been known to cause a major human epidemic, let alone a pandemic.
It appears H5N1 may not behave as the 1918 virus. However, that does not mean that it will not infect humans eventually. We still do not understand influenza virus evolution well enough to predict when it will jump to humans, what mutations are necessary or how virulent it will be when it does jump.
Reenforcing my last paragraph, the authors end with this cheery thought
Even with modern antiviral and antibacterial drugs, vaccines, and prevention knowledge, the return of a pandemic virus equivalent in pathogenicity to the virus of 1918 would likely kill >100 million people worldwide. A pandemic virus with the (alleged) pathogenic potential of some recent H5N1 outbreaks could cause substantially more deaths.
I will talk more about other articles from this issue in my next installment. This is cross posted at my science blog