(17.5%) Eurasian swine (17.5%) – Pig origin Quadruple genetic re-assortment – coinfection with influenza viruses from diverse animal species. Due to coinfection, the viruses are able to interact, mutate, and form a new strain to which host has variable immunity. New events of reassortment were not reported until 1968, when the avian strain H1N1 infected humans again; this time the virus met the strain H2N2, and the reassortment originated the strain H3N2. This strain has remained as a stable flu strain until now. The mid-1970s were important for the evolution of flu strains. First, the re-emergence of the human H1N1 strain became a seasonal strain. Then, a small outbreak of swine H1N1 occurred in humans, and finally, the human H2N2 strain apparently became extinct. Around 1979, the avian H1N1 strain infected pigs and gave rise to Euroasiatic swine flu and H1N1 Euroasiatic swine virus, which is still being transmitted in swine populations. The critical moment for the 2009 outbreak was between 1990 and 1993. A triple reassortment event in a pig host of North American H1N1 swine virus, the human H3N2 virus and avian H1N1 virus generated the swine H1N2 strain. In 2009, when the virus H1N2 co-infected a human host at the same time as the Euroasiatic H1N1 swine strain a new human H1N1 strain emerged, which caused the 2009 pandemic. The swine flu spreads very rapidly worldwide due to its high human-to-human transmission rate and due to the frequency of air travel. See also COVID-19 pandemic Notes Further reading External links Official swine flu advice and latest information from the UK National Health Service 8 minute video answering common questions about the subject on fora.tv Swine flu charts and maps Numeric analysis and approximation of current active cases "Swine Influenza" disease card on World Organisation for Animal Health Worried about swine flu? Then you should be terrified about the regular flu. Centers for Disease Control and Prevention (CDC) – Swine Flu Center for Infectious Disease Research and Policy – Novel H1N1 influenza resource list Pandemic Flu US Government Site World Health Organization (WHO): Swine influenza Medical Encyclopedia Medline Plus: Swine Flu Health-EU portal EU response to influenza European Commission – Public Health EU coordination on Pandemic (H1N1) 2009 Animal viral diseases Health disasters Swine diseases Influenza Pandemics Articles containing video clips