Pyrogen (fever)

Fever, also known as pyrexia and febrile response, is defined as having a temperature above the normal range due to an increase in the body's temperature set-point. There is not a single agreed-upon upper limit for normal temperature with sources using values between 37.5 and 38.3 °C (99.5 and 100.9 °F). The increase in set-point triggers increased muscle contraction and causes a feeling of cold. This results in greater heat production and efforts to conserve heat. When the set-point temperature returns to normal a person feels hot, becomes flushed, and may begin to sweat. Rarely a fever may trigger a febrile seizure. This is more common in young children. Fevers do not typically go higher than 41 to 42 °C (105.8 to 107.6 °F).
A fever can be caused by many medical conditions ranging from the not serious to potentially viral, bacterial and parasitic infections such as the common cold, urinary tract infections, meningitis, malaria and appendicitis among others. Non-infectious causes include vasculitis, deep vein thrombosis, side effects of medication, and cancer among others. It differs from hyperthermia, in that hyperthermia is an increase in body temperature over the temperature set-point, due to either too much heat production or not enough heat loss.

serious. This includes Treatment to reduce fever is generally not required. Treatment of associated pain and inflammation, however, may be useful and help a person rest. Medications such as ibuprofen or paracetamol may help with this as well as lower temperature. Measures such as putting a cool damp cloth on the forehead and having a slightly warm bath are not useful and may simply make a person more uncomfortable. Children younger than three months, people with serious medical problems such as a compromised immune system, and people with other symptoms may require medical attention. Hyperthermia does require treatment.
Fever is one of the most common medical signs. It is part of about 30% of healthcare visits by children and occurs in up to 75% of adults who are seriously sick. While fever is a useful defense mechanism, treating fever does not appear to worsen outcomes. Fever is viewed with greater concern by parents and healthcare professionals than it usually deserves, a phenomenon known as fever phobia.

Pyrogens
A pyrogen is a substance that induces fever. These can be either internal (endogenous) or external (exogenous) to the body. The bacterial substance lipopolysaccharide (LPS), present in the cell wall of some bacteria, is an example of an exogenous pyrogen. Pyrogenicity can vary: In extreme examples, some bacterial pyrogens known as superantigens can cause rapid and dangerous fevers. Depyrogenation may be achieved through filtration, distillation, chromatography, or inactivation.

Hypothalamus
The brain ultimately orchestrates heat effector mechanisms via the autonomic nervous system. These may be:

• Increased heat production by increased muscle tone, shivering and hormones like epinephrine (adrenaline)
• Prevention of heat loss, such as vasoconstriction.

In infants, the autonomic nervous system may also activate brown adipose tissue to produce heat (non-exercise-associated thermogenesis, also known as non-shivering thermogenesis). Increased heart rate and vasoconstriction contribute to increased blood pressure in fever.

Usefulness
There are arguments for and against the usefulness of fever, and the issue is controversial. There are studies using warm-blooded vertebrates and humans in vivo, with some suggesting that they recover more rapidly from infections or critical illness due to fever. Studies suggest reduced mortality in bacterial infections when fever was present.
In theory, fever can aid in host defence. There are certainly some important immunological reactions that are sped up by temperature, and some pathogens with strict temperature preferences could be hindered.
Research has demonstrated that fever assists the healing process in several important ways:

• Increased mobility of leukocytes
• Enhanced leukocyte phagocytosis
• Endotoxin effects decreased
• Increased proliferation of T cells

Management
Fever should not necessarily be treated. Most people recover without specific medical attention. Although it is unpleasant, fever rarely rises to a dangerous level even if untreated. Damage to the brain generally does not occur until temperatures reach 42 °C (107.6 °F), and it is rare for an untreated fever to exceed 40.6 °C (105 °F).


Conservative measures

Some limited evidence supports sponging or bathing feverish children with tepid water. The use of a fan or air conditioning may somewhat reduce the temperature and increase comfort. If the temperature reaches the extremely high level of hyperpyrexia, aggressive cooling is required. In general, people are advised to keep adequately hydrated. Whether increased fluid intake improves symptoms or shortens respiratory illnesses such as the common cold is not known

Medications
Medications that lower fevers are called antipyretics. The antipyretic ibuprofen is effective in reducing fevers in children. It is more effective than acetaminophen (paracetamol) in children.

Ibuprofen and acetaminophen may be safely used together in children with fevers. The efficacy of acetaminophen by itself in children with fevers has been questioned. Ibuprofen is also superior to aspirin in children with fevers. Additionally, aspirin is not recommended in children and young adults (those under the age of 16 or 19 depending on the country) due to the risk of Reye's syndrome.
Using both paracetamol and ibuprofen at the same time or alternating between the two is more effective at decreasing fever than using only paracetamol or ibuprofen. It is not clear if it increases child comfort. Response or nonresponse to medications does not predict whether or not a child has a serious illness