Swine H1N1 Sequences in Human Seasonal Flu
Recombinomics Commentary
October 25, 2007
But now pig farmers are specifically being encouraged to get the shot to protect themselves and those around them since they could spread the flu to their livestock.
According to the Centers for Disease Control and Prevention Web site, pigs can be infected with both human and avian influenza viruses in addition to swine influenza viruses.
The above comments reflect recently released human and swine sequences which demonstrate exchanges of influenza genetic information. Human seasonal flu sequences from patients infected with H1N1 earlier this year have a number of swine polymorphisms in multiple gene segments. These acquisitions signal dual infections involving human and swine influenza.
The acquisitions were supported by recently released swine sequences collected between 2005 and 2007 throughout the United States. These H1 isolates had human HA genes, which were most closely related to seasonal flu isolates from 2003. One series was closely related to H1 from H1N1 isolates, while the other set was most closely related to H1 from H1N2 human isolates in 2003.
These isolates were in addition to earlier swine isolates from the United States and Canada which had human H1 most closely related to human H1N1 from the mid 90’s. The human sequences in the swine evolved more slowly than the sequences in humans, which led to the relatedness in earlier isolates.
However, one of the recent swine isolates, A/Swine/Iowa/01532/2007, had H1 closely related to the 2007 human H1N1 isolates. The swine sequence was from a sample collected March 21, 2007, so additional examples may be present in sequences that have not yet been released.
The recent CDC weekly (week 40) report on influenza in the United States also noted three human cases in Ohio and Illinois which had been infected with swine influenza.
The movement of human influenza into swine, as well as swine influenza into humans is cause for concern. The human sequences in swine evolve more slowly and acquire swine polymorphisms. These infections can act as a reservoir of early human as well as swine polymorphisms which can move into seasonal flu via recombination. Similarly, the acquisition of human polymorphisms in swine increases regions of identity, which can facilitate additional recombination.
The 1918 pandemic H1N1 was a recombinant with human H1N1 and swine H1N1 sequences, which raises concerns about the increased movement of swine and human sequences between the two species.
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