Fever - Febrile, Sub-febrile, Hyperpyrexia, intermittent fever, continuous fever

Fever Explained under 5 minutes. Fever Causes and Treatment,
Human average Temperature is 36.7 degree Celsius.
Normal Range is from 36 to 37.4 degree Celsius. it means, for some people normal temperature is lower, such as 36 and for some, it is much higher.
Rectal or vaginal temperature is slightly higher by 0.5, compared to axillary temperature.
Most sensitive temperature measurement is rectal temperature, because other type of measurement are not precise enough and can falsely exclude fever.
There is not a single agreed-upon upper limit for normal temperature, but for most cases:
Less then 35 is Hypothermia; up to 37.5 is normal temperature.
More then 37.5 is a fever.
Temperature between 37.5 to 38 is called sub-febrile temperature. Generally high temperature then normal is called Febrile.
More then 40 is Hyperpyrexia.
There are different types of fever exist.
Continuous fever is a type or pattern of fever in which temperature does not touch the baseline and remains above normal throughout the day. Such fever is mostly caused by infections like: bacterial pneumonia, infective endocarditis and tuberculosis.
Intermittent fever, where the temperature elevation is present only for a certain period, then normal for several hours. Intermittent fever is caused by malaria, leishmaniasis, pyemia and sepsis.
Pel–Ebstein fever is a rarely seen condition noted in patients with Hodgkin's lymphoma, in which the patient experiences fevers which cyclically increase, then decrease over an average period of one or two weeks.
Fever is regulated by brain, hypothalamus specifically. It senses pyrogenic cytokines and increases body temperature.
There are two main way to increase body temperature: elevation of body temperature by shivering.
And decrease heat loss by peripheral vasoconstriction.
The high limit for body temperature is 41.1 degree Celsius. The higher temperature is rare if there is no structural damage of hypothalamus.
Fever, Generally is an infection predictor.
Common causes of Fever are infections: viral infections: influenza, the common cold, COVID-19, meningitis, urinary tract infections, appendicitis, Lassa, and malaria.
Fever in elderly more commonly indicates bacterial infection in the body.
Fever can be characteristic of cancer also, Especially Hodgkin lymphoma.

Fever plus Rash and Eosinophilia defines the drug reactions.
High body temperature in the first trimester of pregnancy may cause birth defects.
Hyperthermia is, when body temperature increases not because of cytokines, but other factors. Like thyroid storm and heat stroke.
This cases are important because, during hyperthermia body’s temperature can exceeded more than 41 degree Celsius and resulted irreversible denaturation of proteins in the brain.
Malignant catatonia is a disorder in which, hyperthermia is accompanied with autonomic instability, and altered mental status.

Serotonin syndrome is a serious drug reaction. It is caused by medications that increases level of serotonin in the body. Such medications are: antidepressants and psychostimulants.
symptoms that can range from mild (shivering and diarrhea) to severe (muscle rigidity, fever and seizures). Severe serotonin syndrome can cause death if not treated.
Management is based primarily on stopping the usage of the precipitating drugs, the administration of serotonin antagonists such as cyproheptadine.
Most Fever is well tolerated. When temperature is less then 40 c antipyretics are effective.
If temperature is more then 41 degree Celsius it is hyperthermia, rather then cytokine induced fever.
This condition is medically emergency.

Regardless of the cause of the fever, alcohol sponges, ice bags and ice-water enemas also ice baths will lower the temperature. It is more effective during the hyperthermia.
Aspirin or acetaminophen in every 4 hours is effective to control fever in most cases.