When there's something wrong with our health, fever is very frequently the first symptom. Most of us feel it's necessary fight it, but is it really? In the article below, Dr hab. Andrzej Bugajski from the JU MC Chair in Pathophysiology answers that question.
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Headaches, muscle pains, shivers, rapid increased respiratory and heart rate – to most of us, these symptoms are very familiar. They tend to be related to fever, i.e. the increase of body temperature above 38 degrees centigrade. Fever is an indicator of the mobilisation of the organism's adaptive and defensive factors. Increased temperature is just one out of many of the symptoms observable during inflammation (our body's biological response to harmful stimuli). Some of the substances produced by our immune system to control the infection are capable of affecting the thermoregulation centre located in the hypothalamus, which in turn causes an increase in temperature.
The importance of endothermy
It's worth to remember that fever is not a disease, or a detrimental side effect of an infection. Fever is an important part of the healing process.
The body temperature of an average human is approximately 37 ºC (ranging from 36.5 to 37.3, based on various factors such as individual characteristics, time of day, menstrual cycle phase etc.). Homeothermy (Greek: homoios – similar, thermē – heat) makes mammals and birds independent from ambient temperature, an evolutionary success which allowed them to colonise all climatic and geographical zone, including those unavailable for ectothermic animals. The average human body temperature is probably the result of an evolutionary compromise between the metabolic rate (the higher the temperature, the higher the rate – which means an increased demand for food) and reaching a temperature high enough to provide protection from infections, mainly mycotic ones. Body temperature also influences other biological processes. For instance, enzymatic reactions slow down as it decreases, and accelerate as it increases. In humans, their maximum activity can be observed at about 38–39 ºC.
Fever – the ability to temporarily increase body temperature – is present in both warm- and cold-blooded animals. It has been present for at least 600 million years (as evidenced by the oldest currently living species able to internally increase their body temperature). The process of evolution did not eliminate it, as it is beneficial for survival, mostly because it protects the organism from infections.
The heat is rising
It costs an organism a lot to increase its temperature. It is estimated that an increase of 1 degree centigrade increases the basal metabolic rate by 15–20% (in some cases, during shivers, it may reach 600%!) and oxygen consumption by 15%. Therefore, fever may only occur in conditions of both sufficient nutrition and oxygenation.
The main advantage of fever is mobilisation of the immune system and stimulation of many of its functions.
According to some researchers, lack of oxygen and energy causes another defensive reaction: hypothermia, a decrease in body temperature. It slows metabolism and lowers the demand for oxygen, increasing the chances of survival. Another interesting fact is that the severity of the fever is not related to the severity of the disease itself. Minor viral infections may cause high fever, while severe illnesses may cause little to no increase in temperature.
The main advantage of fever is the mobilisation of the immune system and stimulation of many of its functions. During fever, white blood cells, or leukocytes, exhibit increased antibody synthesis, migration and phagocytosis (a process in which the cell engulfs another entity, e.g. a bacterium). The organism uses "emergency supplies", created by accelerated biochemical processes in an increased temperature. Production of collagen used to repair potential wounds is also increased, along with several substances which perform defensive functions: acute-phase proteins (they allow doctors to determine the severity of the inflammation), interferon (a protein responsible for fighting harmful microorganisms), T lymphocytes and specialised NK cells (Natural Killers). Because of this, deliberate increases of temperature (hyperthermia) is often employed in cancer treatment, as it reinforces the effects of medication.
At war with microbes
Fever causes a decrease in the development and multiplication of many bacteria and viruses. Some pathogenic agents develop faster in normal temperature, and increasing it makes them vulnerable. Rhinoviruses, which live on the mucous membrane of our noses and are responsible for most infections in humans, are the best example of that. The optimal temperature for them is about 33 degrees (e.g. when they're cooled by cold air), but their growth is halted when fever causes the mucous membrane to reach the temperature of 37 ºC.
Another way of fighting bacteria is lowering the levels of iron, zinc and copper necessary for them to thrive. During fever, these metals are "hidden" and become unavailable for the bacteria.
It's worth to remember that fever is not a disease, or a detrimental side effect of an infection. Fever is an important part of the healing process. Research shows that allowing fever to run its course may reduce the length and severity of the common cold and flu. Children with chickenpox are sick for a longer period of time if they are treated with antipyretics. 90% of parents try to reduce fever immediately after they learn about it. We shouldn't do that! Fever is a sign that the organism is fighting. We should only act if the fever is long and severe.
Original text: www.nauka.uj.edu.pl
