CH 105 - Chemistry and Society

1918 Pandemic and Avian Flu



The following are Moodle readings (under influenza) that discuss the 1918 virus and the recent avian influenza virus

What Happened in 1918?


1918 "Spanish" flu Distinguishing features:

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Credit:  Influenza 1918 - The American Experience

Credit:  Influenza 1918 - The American Experience

What Made the Virus So Deadly

Possible Reasons


Characteristics of Epidemic/Pandemic Viruses

Date Subtype Comments Molecular Changes
1918 H1N1 pandemic "Spanish" Flu  
1957 H2N2 pandemic "Asian" flu antigenic shift
1962 H2N2 epidemic antigenic drift
1964 H2N2 epidemic antigenic drif
1968 H3N2 pandemic "Hong Kong" flu antigenic shift
1976 H1N1 swine flu  
1999 H5N1 avian flu  


Avian Flu

Strain Location



H5N1 Hong Kong 1997 6/18
H9N2 Hong Kong 1999 0/2
H5N1 Vietnam 2004 20/27
H5N1 Thailand 2004 11/16

Proteins from 1918 Influenza Virus (Type A)  

1918 HA has:

1918 NA:

Using a process called reverse genetics, individual 1918 genes can be added to present strains to make hybrid virus.  These can be used in test animals such as mice or human cells in culture.

Structure Files:


Stevens, J. et al. Structure of the Uncleaved Human H1 Hemagglutinin from the Extinct 1918 Influenza Virus.  Science, 303, pg 1866 (2004)

Gamblin, S. The Structure and Receptor Binding Properties of the 1918 Influenza Hemagglutinin. Science, 303, pg 1838 (2004)

Genetic Changes in the Virus - What Caused the Pandemic

Antigenic Drift

Antigenic Shift


Evidences suggest that before 1918, the major strain of influenza was H3N8.   This was replaced in the 1918 pandemic when an H1N1 virus arose.   In the next pandemic (Asian,1957)  three genes from avian influenza (PB1, HA, and NA) replaced their counterparts in the H1N1 strain, presumably through reassortment as shown above, to give the pandemic strain H2N2.  Again through a similar process, the PB1 and HA genes from the prevalent strain where replaced by avian genes to produce the Hong Kong H3N2 pandemic strain.

In addition, the sequence of viruses can be compared and phylogenetic tree can be created, not unlike family trees of inheritance.  The 1918 virus appears most related to human and swine influenza virus, not avian, but it does clearly have avian features (such as the gene for HA described above).  It may have emerged from avian reservoir before 1918, for which no specimen has yet been found to compare.  That virus may have then acquired enough mutations to make it infective in mammals.  There is yet another possibility:  the 1918 virus came directly from a completely different avian source (somewhat like SARS which emerge from civets).

The 1957 and 1968 pandemic virus had new avian-like HA.  These Probably arose from reassortment, as described above.


Could it happen again?  The avian flu scare

The Avian Flu Links

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