Where the new H1N1 came from

Mixing of flu viruses to produce a new strain. copyright Russell Kightley Media

In Nature 459, 1122-1125 (25 June 2009): Smith et al. on “Origins and evolutionary genomics of the 2009 swine-origin H1N1 influenza A epidemic“.

In March and early April 2009, a new swine-origin influenza A (H1N1) virus (S-OIV) emerged in Mexico and the United States1. During the first few weeks of surveillance, the virus spread worldwide to 30 countries (as of May 11) by human-to-human transmission, causing the World Health Organization to raise its pandemic alert to level 5 of 6. This virus has the potential to develop into the first influenza pandemic of the twenty-first century. [I thought a pandemic alert level of 6 meant it had already?? – Ed] Here we use evolutionary analysis to estimate the timescale of the origins and the early development of the S-OIV epidemic. We show that it was derived from several viruses circulating in swine, and that the initial transmission to humans occurred several months before recognition of the outbreak. A phylogenetic estimate of the gaps in genetic surveillance indicates a long period of unsampled ancestry before the S-OIV outbreak, suggesting that the reassortment of swine lineages may have occurred years before emergence in humans, and that the multiple genetic ancestry of S-OIV is not indicative of an artificial origin. Furthermore, the unsampled history of the epidemic means that the nature and location of the genetically closest swine viruses reveal little about the immediate origin of the epidemic, despite the fact that we included a panel of closely related and previously unpublished swine influenza isolates. Our results highlight the need for systematic surveillance of influenza in swine, and provide evidence that the mixing of new genetic elements in swine can result in the emergence of viruses with pandemic potential in humans.
[my bolded sections – Ed]

An important paper for a number of reasons – not the least of which is pigs have

Depiction of virus mixing in a pig

been pushed to the fore as a potential source of new and dangerous human flu viruses.

Through no fault of their own, I might add: the only pigs proven to have had the new virus were probably infected by a handler who had been to Mexico!

The most important observation to emerge from this is that pigs should be surveilled systematically and worldwide – to stop yet another possible avenue for zoonotic infection for us vulnerable humans.

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3 Responses to “Where the new H1N1 came from”

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  3. H1N1 – view on a pandemic « ViroBlogy Says:

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