Swine "Flu" pandemic - mixed DNA means NOT JUST FLU

It turns out this virus is highly unusual, a quadruple reassortant. The genes of a flu virus are packaged in eight discrete segments. When two flu viruses infect the same host cell, the segments of each are copied and repackaged, 8 at a time, in new viral particles which then bud off from the infected cell. They then may infect a new host cell. In this repackaging process the segments of the two different viruses may mix and match, so that new virus particle will have segments from two different viruses. The new virus is, in a sense, not just a swine flu virus. It does have viral segments characteristic of two different families of swine flu, one typical of North America, where swine flu is endemic, and one typical of pig flu viruses from Europe and Asia. But we learned today that it also has viral segments seen in North American birds and in human seasonal influenza. Which of the segments is a bird segment and which is humans wasn't discussed in today's briefing, but the fact that the genetic sources comprise widely different geographies and species is highly unusual -- unusual at least as far as we know. We have little systematic information on swine viruses, so how common this really is we don't know for sure, nor do we know how recent. The virus is resistant to the older adamantane antivirals but sensitive to both oseltamivir (Tamilfu) and zanamivir (Relenza).

Whatever this is, it isn't seasonal influenza. The reported cases range from 9 years old to 54 years old, 3 females, 4 males. All have recovered and only one required hospitalization. The earliest case is from late March, the most recent just days ago. Symptoms are typical for influenza-like illness except that there seems to be a greater prominence of gastrointestinal symptoms (nausea, vomiting, diarrhea) along with the respiratory symptoms and fever. CDC emphasized they were in an active investigation mode and will keep sharing information as it develops. Clearly there is a lot more to learn about this.

Could this be the harbinger of an influenza pandemic? A pandemic is a global sized outbreak from a single strain of influenza. We believe that there are several necessary conditions for this to happen with influenza. One is the ability of the viral strain to infect humans (there are many influenza viruses but most don't infect humans). Another is the ability to be transmitted from person to person. While bird flu can infect humans, it still has not acquired the ability to spread easily from person to person. Yet another is an influenza virus which is sufficiently different that there is little natural immunity in the human population. As far as I can tell, this virus seems to have all of these characteristics.

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