Epidemics in a Changing World - Department of Innovation, Industry ...

Text Box 1: The new H1N1 influenza, April 2009
EpidemICs in a Changing World
Report of the Expert Working Group
2
The emergence of “swine-lineage” A(H1N1) influenza virus infections in humans and
their transfer to swine occurred during the compilation of this report. New strains of
seasonal human influenza viruses arise almost annually, requiring the regular updating
of seasonal influenza vaccines. However, the emergence and spread of a distinctly
new influenza virus, like the 2009 H1N1 virus, has occurred only a few times in the last
century. Neither the timing nor the location of such events can be predicted. Such is the
nature of most emerging infectious diseases.
The new H1N1 virus is believed to have developed when one human or animal was
co-infected with two different influenza viruses previously identified in swine in North
America and Eurasia. 1 Because the genetic material of influenza viruses is divided into
eight separate segments, co-infection allows “reassortment” to create new combinations
of the eight segments. Occasionally reassorted viruses are infectious and spread
successfully. Whereas the 1918 pandemic influenza virus appeared to arise by mutation
of an avian influenza virus, the 1957 and 1968 pandemics were both caused by reassorted
viruses with new combinations of human and avian influenza genes. 2
(Anne Kelso, pers.comm.)
Figure 1: Quarantine camp, South Australia, in the 1918–19 influenza pandemic
Source: State Library of South Australia. Reproduced with permission of the copyright owner.