Part II: Yet another primer on influenza
I know everyone is inundated with information about influenza these days. Still, a little about the basics makes sense in the context of my post, so here goes.
I've seen quite a few gaps in the explanation offered on the evening news, and I'm going to make an effort to fill some of those in. In the process, I hope to perhaps debunk a few of the myths that are circulating about what flu is and what it isn't. Bear with me, or skip ahead to part three, if you like. You may, with good reason, question my medical background and authority to write these definitions. No, I am not a doctor. But I am a great researcher, and what I have compiled here is based on that:
What influenza is:
A super-simple way to think of influenza is as a virus with an outer "shell." The shell is studded with two distinct glycoproteins, one which is sort of long and spiky, and one which is sort of squat and mushroom-shaped. Long and spiky is called hemagglutinin, or "H" for short. Shorty mushroom-shape is an enzyme (also a protein) called neuraminidase, or "N."
When a specific influenza is categorized, it is typed according to the proteins present on its shell. As of this writing, there are at least 16 variations of the "H" protein, and nine of the "N" enzyme. When you see "H1N1," you are seeing a name that refers to the types of surface structures on that specific strain of influenza.
Influenza is also categorized into types A, B, and C. These classifications, which dates back to the 1930s, offer a basic means of determining a variety of influenza, but they are quite general. The H1N1 circulating in 2009 is Influenza A.
When a type of flu is called "novel," as this year's H1N1 happens to be, it refers to a "new" strain of flu, essentially a combination of genetic material that hasn't been circulated before in a human population. The bits of genetic code in the novel flu aren't immediately recognized by most human immune systems. And all of this translates to more people becoming infected. People who study pandemics are especially interested in novel influenza.
How it is transmitted:
You know the basics about this: Tiny airborne particles from those already infected will expose you to the virus. You get these from breathing them in (from someone's cough or sneeze--ick!), or from touching a surface on which these little guys have been camping out. (By the way, they can wait patiently for a host for anything from a minute up to 48 hours, depending on the surface and the environment.) Once it gets into you (through your mucus membranes like eyes, mouth, nose), it basically turns you into a flu factory. The mechanism of how flu infects its hosts and replicates itself (humans and animals) is fascinating and frighteningly efficient. For a great example of a video that depicts it, check out this piece by Harvard's Medical school.
How it changes:
Influenza is a constant invader to humans because it's highly adaptive. First, the proteins on the surface change pretty frequently. Each change makes a slightly new virus, one that is newly unrecognizable to the human immune system. This is why the seasonal flu from last year is always different from the seasonal flu the year before, and so on. In an attempt to help create a wide range of antibodies for those vaccinated, each year's vaccine actually includes bits from several strains circulating the year before.
Influenza has yet another trick: when it replicates its RNA, the virus can exchange bits of genetic material with other influenza variants, even variants that infect primarily animals. This is why some strains of influenza have genetic material from avian or swine flu, or both. This year's version of H1N1 actually has all three.
What actually happens when a person gets infected with seasonal flu:
You know how this one goes, too. The symptoms of flu are generally related to the human immune system trying to expel the virus. Generally, after a 1-4 day incubation period, influenza has an extremely quick onset, that hits a person like a ton of bricks. Common symptoms are the headache, body aches, fever, chills, shaking, cough, sore throat, and weakness. If it's flu, you are flat-out sick in bed for at least 2 or 3 days, and more likely 5-7. Basically, it sucks. It's not uncommon for a cough to hang around after flu for up to 5 weeks, and post viral weakness can linger, too, for several weeks, especially in adults.
And for novel H1N1? What happens?
Well, keep in mind first that H1N1 is an influenza. The symptoms are similar. But because it is an influenza, it also has a range of symptoms and severity. I think it's worth noting that the Centers for Disease Control (CDC) has stated that a fever is not always present with this flu. The cough seems to be universal, as do the aches, fatigue, and sore throat. The incubation time is similar to a seasonal flu (1-4 days), and the recovery time is similar as well, but a person is contagious for at least one day after the symptoms disappear and--more problematic--a full day before the symptoms begin. Additionally, there is some speculation that the virus continues to be contagious several days after symptoms have abated, especially in children. The symptoms that can linger for weeks include a generalized weakness and a cough.
That is the very basic outline of what flu is. But my concern about influenza, and this particular strain, has more to do with what flu is not, than what it is. And that is the subject of Part III.
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