Fevers and Aches: What a Cold Actually Does

Adeno-Associated virus
The rhinovirus pictured above is just one of the many viruses capable of causing what we call the common cold (Image source: virology.wisc.edu)

So this past week I managed to catch whatever bug has been going around and ended up couch-ridden for a few days. As I lay there in my achy, feverish, continually half-asleep stupor watching old Batman cartoons on the internet, I couldn’t help but get a little curious about the biology of a cold. So in honor of my recent illness, I now present to you a few tidbits on what the common cold is and does.

The common cold is a viral infection of the upper respiratory tract, which basically amounts to your nose and throat. You may have heard that there’s no cure for the common cold and there’s a reason for that: according to the Mayo Clinic, it can be caused by over 100 different viruses. Since the cause is so variable, symptoms tend to vary too. That’s why some colds give you watery eyes and a runny nose, while others give you a cough and heavy congestion, and still others set you back with a fever and sore throat. For simplicity’s sake, I’ll just take a look at two of the symptoms that kept me in last week: a fever and aches.

We all know what a fever is, and a lot of people know it’s a part of the body’s immune response to whatever microbe is wreaking havoc throughout your innards. But why get hot? What does that accomplish? And how does your body even manage that? Well, let’s start with the basics. As defined by Medilexicon’s medical dictiornary, a fever is:

A complex physiologic response to disease mediated by pyrogenic cytokines and characterized by a rise in core temperature, generation of acute phase reactants, and activation of immune systems.

Which is not all that helpful really. So let’s walk through it: Pyrogenic cytokines are basically just signaling molecules that trigger a fever. Cytokines are produced by white blood cells when they come into contact with some indicator of an infection and kick off a wide variety of inflammatory responses. Pyrogenic just means it creates a fever (hence the pyro), so these particular cytokines work their way across the blood-brain barrier and into the central nervous system where they tell your body to increase your core temperature, which it promptly does, thus turning you into a boiling hot wreck on the couch.

images
Cytokines act as intercellular signals that can trigger a number of biological processes within the body (Image source: http://www.qiagen.com)

So what does this accomplish? Well a fever state helps to inhibit bacterial growth, increase the activity of immune cells like neutrophils and monocytes, increase iron sequestration (which is vital for a number of immune processes), and relegate you to bed so you can’t get any sicker. Fevers can get problematic if they get to high, but for your average cold, they’re mostly just mildly inconvenient.

Now what about those aches? What about being sick makes your every joint feel like its stuffed full of cotton balls made only of dull misery? When antibodies or an immune cell attach to a microbe from outside the body, they form what immunologists call an immune complex. As it would happen, immune complexes often get deposited in your joints where they trigger an inflammatory response, which is what actually causes the joint pain associated with a cold. This particular symptom is basically a mild and temporary form of arthritis. So, in other words, to get rid of your cold, your body gives you arthritis. Such a beautiful machine, the human body.

If you want to avoid getting a cold, do what everyone has always told you to do. Wash your hands regularly, avoid close contact (especially with people who are clearly sick), and disinfect everything in sight. That should probably keep you healthy. I certainly didn’t do any of that and I got sick, so it seems like a safe plan.

For more information on how the fever works, here’s where I got my information (beware, it’s scholarly):

http://cid.oxfordjournals.org/content/31/Supplement_5/S178.full

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