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Pyrexia is the medical term for fever. If your body temperature increases to beyond 37.2° C, and you begin to sweat, breathe deeper and feel warmer, that's when I tell you that you are running a fever. The commonest cause of fever is the simple cold. This condition is well known to all of us, with the scratchy throat and runny nose. The body thermostat is found in the hypothalamus within the brain. Pyrogens are a group of substances released from inflammatory cells, which have the capability of resetting the hypothalamic thermostat to increase body temperature. Inflammatory cells spring into action when the body is invaded by foreign viruses or bacteria. If I increase your central thermostat by a few degrees, your body will think that it is too cold, and you get that "chilled" feeling. This explains one of the great myths of colds. Many mothers tell their children that the reason they got a cold is because they went outside poorly dressed and got chilled. In reality, the cold virus is highly contagious and there is a time delay between the virus invading through your nose and developing symptoms. Being out in the cold has nothing to do with contagiousness, it simply exaggerates the chilled feeling.
Pyrogens can be produced by viruses and bacteria or by many cells in our immune system. In this way, fever is a beneficial state in which our immune system seems to function better. Increased body temperature increases our body enzymatic processes and facilitates the quick mobilization of our immune system. Technically, fever is not due to infection but tells you that your body is fighting back. We also see fever with other entities such as cancer. A group of glycoproteins produced by immune cells is called the Tumor Necrosis Factor (TNF), which turns up the thermostat in the hopes of having immune cells mobilize towards cancer cells. It is high fever of over 40° C that we express concern because it may signal an overwhelming of our system. This could result in malfunctioning of cellular machinery leading to febrile seizures in children. This is why we advocate the use of anti-pyrogens such as acetaminophen to control the amount of fever and discomfort.
The common cold is actually caused by hundreds of different and related viruses. Your body will respond to over a hundred different cold causing viruses during an average lifespan. A great many of these cold illnesses will occur in the first part of life. Immunity is thought to be permanent after each bout. Colds are not caused by a "weakened" immune system. This is a myth. If I take 100 people, put them in a room and spray in a new cold virus, about 90 people will become infected. But 25 of those infected will have their immune system quietly deal with it and show no symptoms at all. Cold viruses are spread not only in the air, but settle on objects when you cough. They can survive there from minutes to hours. Washing our hands and covering our mouths are still the best defense. Colds rarely keep healthy people from school, work or lending a hand when your team needs to put a few buffalo chips in the net on the frozen pond! So, try and stay healthy this season. And get those skates sharpened!
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