What with headlines reading “U.S. prepares for possible swine flu epidemic as global cases rise” and “Swine Flu Confirmed in New York Students,” it’s time to talk about the disease a little more.
We’ve addressed flu before:
Why is “How To Wash Your Hands” a flu post? Because hand washing is the #1 public health measure you can take. Here’s the full list:
The #1 public health measure the authorities can take is close the schools.
The CDC have put up a page about Taking Care of Yourself: What to Do if You Get Sick with Flu; another page about Taking Care of a Sick Person in Your Home; and a What’s New on the Swine Flu updates page.
If you want a crystal ball, I recommend The Great Influenza: The Story of the Deadliest Pandemic in History by John M. Barry. It also has a great deal of fascinating history of nineteenth and early-twentieth century medicine, and the men and women who pretty much created medicine as we know it.
Now let’s talk a little more about influenza.
The flu is a funny bug. As you know, Bob, it’s a virus, and a virus isn’t really alive. A virus is just a strand of nucleic material in a capsule or shell. It needs to find a living cell. It injects its nucleic material into the cell, and the cell (taken over by pirates, as it were) gets to work making lots more viruses.
I discussed the immune system in Why We Immunize, but I’m going to go over it a bit more here.
You must know that proteins have shapes, and those shapes are how you can tell one protein from another. Your cells are covered with protein, viruses have protein capsules, it’s all protein on the molecular level.
Your immune system (when it’s working right) recognizes self and non-self. It protects the self and attacks the non-self. It does this in a couple of ways. First, you have generalized reaction. When cells are distressed, they release cytokines, and those switch on a kind of white cell called the NK-cell. NK stands for Natural Killer (no, I’m not making this up). The NK cells find anything they don’t recognize, and, using specialized proteins, destroy it. When you’ve got an infection, those are the first things that come on line.
The next thing to arrive are the antibodies. These are specialized cells that are keyed to find one specific protein—the foreign invader protein—and destroy it. Before your body can produce antibodies, it has to have been exposed to the antigens (which is what you call non-self proteins), and be sensitized.
Meanwhile, your body is releasing enzymes, hormones, peptides, and other chemicals that act as messengers to produce various effects. Fevers, swelling, sweating, headache … all enzymes. The aching in your bones that you feel is the marrow pumping out white cells to fight the infection.
Once your body has successfully fought off an invader, the antibodies remain. If they ever again encounter proteins of the same shape, they’ll be on ‘em fast. The infection won’t have a chance to start.
Now, your influenza virus is a simple one. It doesn’t even have DNA in it. It has strands of RNA in its center. RNA mutates pretty fast. But here’s the really tricky part about the flu: it has a sneaky way of getting past the immune system, even if you’ve had the flu before. The shell or capsule that surrounds that RNA is made of two proteins, hemagglutinin and neuramidinase. Hemagglutinin and neuramidinase can move like the tiles in a sliding-block puzzle, presenting different protein shapes to your antibodies. Hemagglutinin and neuramidinase are the H and N that you see when people talk about Influenza H5N1 or H1N1 or H3N2 or what-may-have-you. There are fifteen known types of hemagglutinin and nine known types of neuramidinase, and they have subtypes below that. Those two substances keep moving around, so that antibodies don’t recognize them. This is called “antigen drift.”
It only gets better after this.
Viruses have the ability to pick up useful traits not just by means of mutation, but by grabbing them from other microbes directly—even across species lines. Flu, moreover, doesn’t have a single strand of RNA inside it—it has unconnected strands. So if two viruses infect the same cell at the same time, the RNA can play mix-n-match, take virulence from one virus and infectivity from another, and come up with something both infective and virulent. (That’s what happens when a swine flu or an avian flu gets loose: Someone has both human influenza and swine or bird influenza at the same time, the two viruses enter the same cell at the same time, and what comes out shares the worst features of both.)
As I keep saying, flu is as simple as drool. It only has eight genes in its genome. Those genes insert themselves into the living cell’s genes, and start producing viruses. In about ten hours, the infected cell explodes and releases somewhere between 100,000 and one million brand-new viruses into the body; and, through coughing and sneezing, into the world. RNA doesn’t have a checksum. And when you have unconnected strands of RNA, you have a high probability of mutation. So all of those million new viruses won’t be exact copies of the original. We’re seeing mutation on steroids, figuratively speaking. Pretty much every possible combination will be present. That means that influenza strains can adapt rapidly to different drugs, to different environments, to different species.
Other RNA viruses include measles and HIV. They’re both nasty. But HIV is very hard to catch, and measles never changes its protein shape so having once had it (or vaccination) lends permanent immunity.
Once influenza starts cooking, you have a lot of virus in your body. And this is where the swine flu gets not just miserable but rapidly lethal. Remember those cytokines, the chemicals released by cells-in-trouble that cry havoc and let loose the Natural Killer cells? Get enough cytokines going, and you’ve got two kinds of trouble. First, those NK white cells they activate are fairly large. In order for them to get to the scene of the infection, the capillaries have to be weakened so that the NK cells can pass through their walls. This also allows fluids to pass through. Your body starts dumping fluids through the capillaries and into your lungs. The ultimate effect is viral pneumonia. If it’s bad enough, you drown.
Second, NKs are very nonspecific. Their basic programming consists of “Something’s not right. Kill it.” That capillary process I just described reads a “damage” to Natural Killer cells, so they start attacking those tissues. Then they call for more help, and cells that weren’t even attacked by the virus get devastated. This feedback loop is called a “cytokine storm.” Effectively, it’s the body necrotizing itself. Once that process starts, stopping it is very tough indeed. That’s what killed so many people in 1919, particularly young, strong people with well-developed immune systems: that influenza attack was so strong that their own immune responses killed them. In some cases, the process could be measured in hours from first symptom to last. Far more, better, actual information in this post in the comment section from Nix.
You don’t need to have everyone sick in order to have a pandemic. Just having 15-40% infected will do nicely. The only question is what the mortality rate among those 15-40% is going to look like.
The next couple of weeks could get interesting. And it ain’t over ‘til it’s over.
Flu Redux by James D. Macdonald is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License.
(Attribution URL: http://nielsenhayden.com/makinglight/archives/011241.html)