: why almost all the diseases bring cold and fever with them?
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Disease dies at high temperatures. So it’s our body mechanism to protect from that disease.
The infecting virus has proteins that help them live and reproduce in our cell (by replication) high temperature denature that protein.
I’m not an expert in biology or have any advanced studies in it but from what I know a fever is the body’s way of trying to kill the disease since most of them die or stop spreading and growing at high temperatures. And you get cold because your brain tells your body it needs to raise the temperature to kill the disease, but until it does you’re under the right temperature for your sick body.
Because of two things.
Firstly, many molecules of pathogens are what we call pyrogens. Pyro meaning heat and gen meaning generate. There is a mechanism in our hypothalamus, which is a part of the brain, that acts like a thermostat and it determines what we call a normal body temperature. If your core body temperature falls below the temperature set by our internal thermostat, the body will try to conserve heat to raise the core temperature to match the one dictated by the hypothalamus. The opposite happens when the core temperature raises above the temperature our internal thermostat dictated.
Pyrogens work by basically hijacking that termostat and adjusting it to a higher temperature.
Now, as a sidenote, i want to take you through the cause and effect of that act just so you can get a bigger picture.
Let’s say internal thermostat is set at 37°C (98.6°F). A pathogen invades and one of it’s metabolic products acts like a pyrogen, therefore raising the thermostat in the hypothalamus. That means that, although the core body temperature is 37/98.6 the body thinks it is cold. That’s why you feel cold while having a fever, because your core body temperature, ehich would otherwise be considered normal, is lower that the temperwture set up by your internal thermostat so the body tries to to catch up by shiverring, not sweating, etc. The moment that you arrive at your new, higher temperature, you stop feeling cold, even though your temperature is well above what we call normal. After some time, your body stops the pathogen from dealing more damage and gets rid of the pyrogen, your internal thermometer returns to it’s normal setting, 37/98.6.
Now you’ve enered what we call a crisis. You see, your body is at the temperature that the thermometer dictated while pyrogens acted, but now that the internal thermometer returned back to normal, your body is at a much higher temperature than the thermometer is now set up. That means that you start lowering your temperature by sweating, and your skin becomes warm. After you lower your temperature to the same one that is dictated by the internal thermometer, you stop sweating and feeling sick. You just survived a whole fever cycle.
Now, the 2nd reason why body temperature rises is because it is beneficial to our immune system, and it hinders pathogens. You see, every enzyme in an cell, and therefore pathogens, is a protein, meaning that it has a range of temperatures where it works best, outside of which, it stops having its function. Not always, but pathogens often can’t survive, or rather can’t thrive, in warmer environments. That’s why systemic temperature elevation can be beneficial because we slow down the metabolism of bacteria and therefore lower their severity.
So, in general, raising body temperature helps our immune system fight off pathogens by lowering their metabolic activity. This can happen locally, at the infected site by the immune cells alone, but can happen in the whole body using the pyrogenic properties of the pathogen’s metabolic products.
To keep it at ELI5 level, the fever that we get during infections is not directly caused by the bacteria/virus/fungus. It is our own bodies response to the invader. Our bodies find an infection and one of its mechanisms to try to deal with and kill it is by increasing our body temperature. So it doesn’t matter what the infection is, one of the symptoms will be a fever
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