Why do we get fevers?

One of the symptoms of coronavirus is a high fever - but why do we get them and can they be dangerous


One of the most prominent symptoms of COVID-19 is fever. So, if you are running a temperature, you should stay at home and self-isolate. When we get a fever, we usually respond by trying to bring our temperature down - usually by taking paracetamol.

But evidence suggests that a fever may be part of your body's strategy for fighting an infection rather than just a by-product of the infection.


What is a fever?

It is normal for your body's temperature to fluctuate throughout the day, and it is often highest in the evenings and lowest in the mornings.


A fever is usually defined as a temperature above 37.5 degrees Celcius (99.5 degrees Fahrenheit), but the temperature you read can vary depending on where you take it from.


When taken in the mouth, the average body temperature is usually between 36.5C (97.7F) and 37.2C (98.96F) but, taken in the armpit, it can be 0.2C to 0.3C (0.36F-0.54F) lower.


During the pandemic, there has been a shortage of thermometers, and without one, it can be difficult to determine whether you have a fever.


To assess whether you might have a fever without the use of a thermometer you can use the back of your hand to feel your forehead, check in the mirror for a flushed face, observe for chills, muscular aches and weakness and assess for dehydration from a fever by checking for darker, more concentrated urine.


How do fevers occur?

Fevers are caused by chemicals called pyrogens which occur when proteins and other toxins are released from the cell walls of bacteria and viruses, or by our own bodies when they come into contact with certain bacteria and viruses.


The pyrogens are released into the bloodstream and then reach the hypothalamus in the brain, our temperature regulation centre. When the pyrogens bind to the receptors in the hypothalamus, this causes shivering and the constriction of blood vessels to help the body temperature reach the new setpoint, resulting in a fever which is part of the body's attempt to kill the pathogen - in this case, the virus.


What are the benefits of a fever?

Fevers are usually self-limiting and are rarely serious in nature. Studies have shown that when your core body temperature increases by between 1C (1.8F) and 4C (7.2F), infections clear up quicker.


It was previously thought that a fever simply created a less hospitable environment for pathogens to survive and replicate, but mounting evidence also shows that a fever optimizes our immune system.


It has been found that certain immune cells (known as T-cells) which are capable of destroying infected cells are enhanced by fevers. In a 2011 laboratory study involving mice, half the mice were warmed by 2C (3.6F) and the other half remained at normal body temperature. It was found that the warmed mice had an increased number of T-cells.


It has also been suggested that excess body heat triggers our T-cells to produce heat-shock proteins (HSPs), which bind to another set of proteins called integrins.


These immune complexes all pull together and stick to blood vessel walls, allowing the immune cells to crawl along the blood vessel walls and migrate to the site of the invading pathogen to attack it.

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