Swine Flu Worries Top CDC Virologist

Many of us non-scientists are asking the question: just how scared should we be of swine flu?

Maybe we should just take our cue from an expert. And if the expert is Ruben Donis, head of molecular virology and vaccines branch at the U.S. Centers for Disease Control and Prevention, then we should be afraid, maybe very afraid.

Donis was recently interviewed with Jon Cohen who blogs for the American Association for the Advancement of Science ScienceInsider blog. Donis said he's concerned because of just how easy it appears this particular virus gets transmitted between humans.

An excerpt:

R.D.: We all pray this remains sensitive to antivirals. We all hope that vaccines will be developed. The virus doesn't grow very well in eggs. We hope the virus will improve [the] ability to grow in eggs so we can produce [a] vaccine very quickly so these secondary and tertiary cases can be controlled. In some countries there's good surveillance, but in others, who knows.

Q: What do you think of this outbreak?

R.D.: This is the first one I've seen firsthand as a virologist. The avian influenza outbreak is not comparable because this is unfolding so quickly. This reminds me of SARS. With avian there's very little transmission. And even with SARS, transmission was far less.

Q: Does this one scare you?

R.D.: I saw figures that do scare you. We've received 300 samples from Mexico, and these cover the span of February, March, and April. And you look at flu A, traditionally it's A/H1 or A/H3 or it's B up until the end of March. There are two or three cases up to [the] last days of March that are swine. Then in April they skyrocket. So all the cases in the D.F. areas, where most samples came from, it really transmits very efficiently.

 

What's striking about about this H1N1 swine flu, Donis says, is how it has learned some new tricks. It's not news that a swine flu virus would jump from pigs to humans. Such cases aren't unknown.

But it's still a rather rare thing for the virus to rearrange genetic material in a way that gives it the ability be transmitted easily between humans. But that is what seems to have happened.

Another excerpt:

Q: What do you know about this swine flu virus?

R.D.: We know it's quite similar to viruses that were circulating in the United States and are still circulating in the United States and that are self-limiting, and they usually only are found in Midwestern states where there is swine farming. There's only one well-documented case where the infection spread from one human to another. What we know is that it is not common that there is sustained transmission in people.

Q: Christopher Olsen published a paper that looked at the literature back to 1958 and only found 50 cases of humans infected with a swine influenza.

R.D.: If we have two documented cases a year, maybe that's just the tip of iceberg. Maybe there are 10 times more or 50 times more. But still, it's only swine to human, and it stops there.

Based on this interview, it seems perfectly reasonable to call this virus swine flu, despite the Obama Administration's desire to get everyone calling the notorious virus by its scientific subtype name, H1N1. This is a virus associated with pigs, plain and simple, according to Donis. Actually, it's not so simple. Donis gets into the weeds, so to speak, of molecular genetics in his explanation:

Q: Is it of swine origin?

R.D.: Definitely. It's almost equidistant to swine viruses from the United States and Eurasia. And it's a lonely branch there. It doesn't have any close relatives.

Q: How about the neuraminidase gene?

R.D.: It has close relatives in Asia. It's also swine.

Q: The matrix gene?

R.D.: The same as neuraminidase.

Q: So where are avian and human sequences?

R.D.: We have to step back [to] 10 years ago. In 1998, actually, Chris Olsen is one of the first that saw it, and we saw the same in a virus from Nebraska and Richard Webby and Robert Webster in Memphis saw it, too. There were unprecedented outbreaks of influenza in the swine population. It was an H3.

Q: They were dying from it?

R.D.: No. It was not very severe in healthy pigs. Everyone was very curious about these H3 viruses. Since 1918, normally it's only H1N1 in swine. Then all of a sudden there's H3N2 in swine in the Midwestern U.S. When people analyzed what was inside those viruses, they realized there were three different things.

The PB1 gene, that was human. H3 and N2 also were human. The PA and PB2, the two polymerase genes, were of avian flu. The rest were typical North American swine viruses.

So swine viruses that swept across hog farms in the U.S. in the late 1990s were seen to have some genetic material from viruses that afflicted birds and humans.

Donis suggests that the current swine flu could have started in the U.S., maybe the Midwest, and then bounced around the world a bit, picking up a little genetic material here, some more over there, before the virus finally got the world's attention in Mexico.

A last excerpt:

Q: It suggests a mixing of pigs from North America and Asia.

R.D.: One little detail we haven't discussed is [that] these Midwestern viruses were exported to Asia. Korea and many countries import from the U.S. Swine flu is economically not such a big deal that many countries don't check for it.

Q: How do you get Europe in there?

R.D.: There are some parts of the puzzle I don't have the answer to. The genetic lineages of Asia and Europe mix quite a bit.

Q: How does the pig get back here?

R.D.: Who said it was a pig that came from Asia? Did I say that? It could be a person.

Fascinating. And scary.