Iowan has swine flu

When people think of Iowa, many of them think of our agriculture (for good reasons). Obviously, it's big business here. We ranked first in the nation in production of corn, soybeans, eggs, and pork in 2005. Indeed, population-wise, hogs here outnumber humans by more than 5 to 1. This is one reason research at our center focuses on zoonotic disease (diseases which can be transferred between animal species), and specifically, diseases of domesticated animals. A story in the news today shows one reason why we study what we do:

Iowa State health officials say someone in eastern Iowa has tested positive for swine flu, a pig disease which rarely jumps to humans.

Doctor Patricia Quinlisk, the state's epidemiologist, says there is no cause for alarm.

The patient was diagnosed with swine flu after a throat swab was taken. The person had developed flu symptoms and went to a doctor.

The U-S Centers for Disease Control and Prevention has confirmed the swine flu diagnosis. The agency has blood tests pending on people in contact with the Iowan to determine exposure.

Quinlisk says there was no evidence the virus has spread person to person. She says the patient was not hospitalized and has since recovered.

It was unknown how the individual contracted the virus.

Quinlisk says swine flu is hard for humans to catch from pigs.

More after the jump...

First, a bit about swine influenza. I've written a bit about it previously here for those who want more background, but essentially, the main swine viruses circulating are of serotypes H1N1, H3N2, and H1N2. (The news report doesn't identify the serotype this person was infected with). Some of these viruses are combinations of human, swine, and avian influenza viruses, and swine have previously been implicated in the generation of pandemic influenza viruses due to their ability to serve as a "mixing vessel" for avian and human-type influenza viruses. And since they're so closely related to humans (well, much more closely related than, say, birds, anyway), there is concern that a swine virus (or an avian virus that becomes adapted to mammals by infecting a pig) could enter the human population and wreak havoc. So, in a nutshell, that's one reason why we're so interested in swine influenza, even though "bird flu" has recently been so dominant in the news. And though this news report shows a fairly simple scenario so far, it raises a lot of unanswered questions.

I'll assume for now that (though not directly stated in the article) the patient is a farmer or other individual who works around hogs, and has been in direct contact with infected swine. I'm assuming this because it's not mentioned in the article that s/he *wasn't* in contact with swine, which would seem an important enough detail to include (to me, anyway). However, I think some of the other statements in the article are less supported.

First, it says, repeatedly, that the virus is difficult for humans to catch from pigs. Likely this is true, but as I've pointed out previously (see here), we don't really know the extent of human infection with swine viruses. When someone comes down with "the flu," 1) it's rare that they even go to the doctor unless the case is serious; and 2) even if they *do* go, the viral isolates are rarely typed. So what we have are a very small subset of isolates that extrapolations are made from, and we know very little about the isolates out there that may cause very mild or asymptomatic infections in humans. Therefore, we really don't know the denominator in this case--the number of swine influenza infections that routinely occur in humans.

Second, it's stated that "there is no evidence that the virus has spread person to person." However, elsewhere in the article it mentions that the blood tests on contacts are still pending. So while the "no evidence" part is likely stated because (I'm guessing) none of the patient's contacts developed symptoms consistent with influenza virus infection, only these tests can confim that they weren't infected sub-clinically. (In other words, that the virus didn't actually spread to them, but not cause symptoms).

Either way, it's an interesting report. I wonder if the patient had any of the risk factors that have previously been identified for swine flu infections....