feuervogel | Swine flu and you! (PSA) (Reply)

luckykitty asked me in comments why this swine flu's got the health types freaked out. (Concerned, really. We're not panicking. Yet.) Isn't it just another flu? While answering, I thought I might as well make it a real post, since others of you might be wondering the same thing. (Note: I'm simplifying a LOT.)

Swine flu is worrisome because it's new. This one, influenza A(H1N1), appears to be a mixture of avian, human, and pig flu viruses. How does that work? Well, influenzaviridae are RNA viruses, so they've just got a bunch of genetic material hanging out. RNA viruses are really lossy, to borrow a CS term. When they copy themselves, it's easy to make a mistake. Also, the flu viruses have a tendency to recombine with other flu viruses. The flu genome is in 8 pieces, floating loose. So if you've got two different flu viruses in a cell, they can mix and match, and you'll get different viruses.

What do those H and N things mean? Well, the flu has two different surface antigens: hemagglutinin and neuraminidase. There are 16 known types of HA and 9 of NA. Not all subtypes can infect all species, but some can infect multiple species. H1N1 is one of them. (I once saw a nice graphic of which subtypes could infect which species, but my google-fu is failing me.)

It's a big deal because the antigens are completely unlike any in human flu strains -- which means we don't have proper antibodies or antibodies similar to the strain. Which means it's harder for our immune systems to fight off. I'm not sure, but that may be part of the reason that young, healthy people are disproportionately affected by it and the cytokine storm hypothesis for 1918 Spanish flu. (Basically, the immune system's first response is cytokines, which are the natural killer cells. They're not very smart, so they come in and say "Us? OK. Not us? KILL IT WITH FIRE!" That gives the body time to mount the antibody response, and when the antibodies come on the scene, the cytokines chill out a bit. But if there's no antibodies, the cytokines keep killing with fire.)

The body remembers everything it's been exposed to that caused it to make antibodies. B cells are the ones that make antibodies, and memory B cells remember them.

So, the flu has antigenic shift and antigenic drift. Drift is a small change in the proteins that the body recognizes as NOT US. Depending on how far it drifted, the memory B cells might be able to help out while new antibodies are being made. Kind of like taking a key that kind of works to open the door while you get a locksmith to make a new one.

Antigenic shift, however, is a lot harder for the body to compensate for. It's something your body's never seen, so there aren't any similar keys to try, and it has to wait for the locksmith to do anything (except the NK cells killing everything with fire.)

What's worrisome is that in Mexico, the fatality rate is pretty high (though we obviously don't know the true number of cases, only the 100 or so potential deaths from swine flu and the 20 confirmed.) In the US, it's true that the cases have been non-fatal and largely mild. (I hesitate to call anything requiring hospitalization "mild.")

US case count today is up to 64. These are laboratory-confirmed cases only. What we don't know, as I mentioned above, is how many people got mild infections earlier and passed it off as a regular flu. Many of the cases have been identified since the news broke from Mexico, and many of them are from the NYC school (45!) where 100 kids were sick. Case-finding efforts are underway, which means that hospitals are searching their records of recent admissions for upper respiratory illnesses to see if any fit the clinical criteria list and testing for influenza if possible (and sending samples to the CDC if they find any suspicious ones.) There's a rapid test that can show if someone has influenza and whether it's influenza A or B; further subtyping requires molecular-level testing. (Influenza B does not have subtypes like A. It's also less common.)

Don't panic. Be concerned, be aware, and be prepared, but don't panic. Add Effect Measure to your daily reading list or RSS aggregator.