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Published online: 24 June 2009 | doi:10.1038/nchina.2009.133

Infectious diseases: Swine flu origin unwrapped

Felix Cheung

Introduction

© (2009) istockphoto.com/Sean Locke

Since its first emergence in March/April 2009, the swine-origin influenza (H1N1) virus has infected 35,928 people in 76 countries (as of June 15¹) through human-to-human transmission. Some early speculation suggested that the H1N1 virus might have been a product of a laboratory accident. However, Yi Guan at the University of Hong Kong, Andrew Rambaut at the University of Edinburgh and co-workers² have findings to prove otherwise.

The researchers used evolutionary analyses to estimate the timescale of the origins and the early development of the epidemic. Their analyses showed a well-established swine influenza lineage in H1N1. This lineage is possible only if the virus had been circulating in swine for 10 years or more before the outbreak.

Their analyses also showed that the H1N1 virus contains genetic elements of avian, human and classical swine origins. The mixed genetic ancestry rules out the possibility of a laboratory accident as the virus origin.

The researchers believe that H1N1 originated from several viruses circulating in swine, and that the initial transmission to humans occurred months before recognition of the outbreak. The findings highlight the pandemic potential of H1N1 and the need for systematic surveillance of influenza in swine and swine workers.

The authors of this work are from:
State Key Laboratory of Emerging Infectious Diseases and Department of Microbiology, Li Ka Shing Faculty of Medicine, University of Hong Kong, Hong Kong, China; Institute of Evolutionary Biology, Ashworth Laboratories, University of Edinburgh, Edinburgh, UK; Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, Arizona, USA; Department of Zoology, University of Oxford, Oxford, UK.

References

1. http://www.who.int/csr/don/2009_06_15/en/index.html
2. Smith, G. J. D. et al. Origins and evolutionary genomics of the 2009 swine-origin H1N1 influenza A epidemic. Nature doi:10.1038/nature08182 (2009). | Article |