Swine flu is sweeping—if not the nation, then at least the nation's media. But what is special about this virus and what, if anything, should ordinary citizens do about it?

The new flu, which has elements of pig, bird and human flu viruses in it, has been circulating for at least a month in Mexico. In the past week, it has popped up north of the border (with 45 cases confirmed in New York City, 10 in California, six in Texas, two in Kansas and one in Ohio), according to the U.S. Centers for Disease Control and Prevention (CDC), as well as in at least five other countries, The New York Times reported yesterday.

As the number of deaths likely caused by the virus in Mexico reaches beyond 150, researchers and public health officials are investigating intensively and anxious to see what the virus does next.

The respiratory virus, influenza A H1N1, is common among pigs (humans actually first passed it to them after the 1918 influenza pandemic), and the porcine version has been known to infect humans before. But rarely does it make its way from person to person, the way this strain is behaving. The fact that this virus has a sustained ability to pass between people has led the World Health Organization (WHO) to elevate its pandemic alert level to 4 (out of 6, the latter being a full-blown pandemic).

One has only to look back a few years to the 2003 scare over SARS (severe acute respiratory syndrome), which ended up causing about 774 deaths worldwide, for a recent measure of the potential for global pandemic panic. But how does this flu measure up to SARS and to other threatening influenza strains like the H5N1 avian flu virus?

To take the pulse of pig flu, we spoke with Chris Olsen, a professor of public health and head of the Olsen Laboratory, which studies influenza A viruses, at the University of Wisconsin–Madison School of Veterinary Medicine.

[An edited transcript of the interview follows.]


We know that this is an H1N1 strain, so what can that tell us about the virus?
There is not anything inherent about the behavior of the H1N1 virus. What it is important to understand is the H1 and H3 are the only subtypes that have ever circulated widely in the swine populations. Certainly there would be more concern if this were a subtype that had never been seen before…. This is not the same thing as H5 [which is] bird flu.

Do we know what's happening at the cellular level? Is anyone testing it yet?
We don't know that yet. Once we get through the public health crisis phase of things, that's going to be one of the important research questions: to look at differences in infectivity in one species and another. This virus might become quite an important tool in teasing apart the phases of the infection cycle. Right now, the key is to get through the initial public health phase. That comes first in terms of protecting human health and human lives, then we can address the research side.

How does this compare with other flu outbreaks?
There are a relatively limited number of documented cases of zoonotic [human-communicable] swine influenza in the literature. Usually they're limited events where a person was in contact with a sick pig…. This is by far the most extensive person-to-person spread that we've seen from a swine-origin virus.