Fever, also known as pyrexia, is a disorder in which the body's temperature increases above its normal range caused by an increase in the temperature setpoint value. There is no universally accepted upper limit for normal body temperature, with reports citing temperatures in humans ranging between 37.2 and 38.3 °C (99.0 and 100.9 °F).

Increased muscle contractions and a sensation of cold or chills are caused by a rise in setpoint value. As a consequence, more heat is generated and more heat conservation attempts are made. Whenever the set point temperature gets back to normal, an individual might feel hot, flushed, and possibly sweat.

A fever will sometimes induce a febrile seizure, which is more common among children. Fever temperature rarely exceeds 41 to 42 degrees Celsius (105.8 to 107.6 degrees Fahrenheit).

Fever could be caused by a number of medical conditions, from mild to life-threatening. The common cold, meningitis, Influenza, urinary tract infections, COVID-19, appendicitis, and malaria are examples of bacterial, viral, and parasitic infections. Vasculitis, connective tissue disease, deep vein thrombosis, drug side effects, and cancer are also non-infectious causes. Hyperthermia, on the other hand, is a rise in temperature of the body above the temperature set point caused by either very less or very high heat output.

Hyperthermia

Hyperthermia is a condition in which the body temperature rises above its fixed point due to either excessive heat output or insufficient heat loss. Heatstroke, malignant hyperthermia, neuroleptic malignant syndrome, stimulants like substituted amphetamines and cocaine, idiosyncratic drug reactions, and serotonin syndrome are examples of high temperature phenomena that are not fevers.

Types

Different trends of recorded patient temperatures were found, some of which could be predictive of a specific medical diagnosis:

Continuous fever (– for example, lobar pneumonia, urinary tract infection, meningitis, typhoid, or typhus), in which the temperature stays above average during the day and may not fluctuate upwards of 1 °C in 24hrs.
Intermittent fever is a form of fever in which the temperature rises for a short time before returning to normal (as in malaria, pyemia, leishmaniasis, or sepsis).
Remittent fever (– for example, infective endocarditis or brucellosis), in which the temperature stays above average during the day and rises and falls by more than 1 degree Celsius in 24 hours.

Hyperpyrexia

Hyperpyrexia is a moderate or serious increase of temperature of body defined as a core body temperature greater than or equal to 40.0 or 41.0 °C (104.0 or 105.8 °F) depending on the source; the spectrum of hyperpyrexia includes cases graded as severe (40 °C) and intense (42 °C). It varies from hyperthermia in which the thermoregulatory system's set point for body temperature is set higher than normal, and then heat is generated to reach it. Hyperthermia, on the other hand, occurs when the body's temperature rises past its fixed point due to external causes.

An intracranial haemorrhage is a major condition of hyperpyrexia. Sepsis, opioid overdose, neuroleptic malignant syndrome, Kawasaki syndrome, serotonin syndrome, and thyroid storm are a few of the factors seen in emergency departments.

Fever Symptoms

Below given are the Fever symptoms:

Sweating
Headache
Chills and shivering
Loss of appetite
Pain in the muscles
Irritability
General weakness
Dehydration

Typhoid Fever

Typhoid fever, also called typhoid, is a bacterial infection caused through Salmonella serotype Typhi. Symptoms can range between moderate to serious and appear anywhere between 6 and 30 days after infection. A high fever typically progresses progressively over many days.

Weakness, indigestion, abdominal pain, headaches, and moderate nausea are common side effects. Many people get a rash of rose-colored spots on their skin. Humans can become confused in serious cases. Side effects can last weeks or months if not treated.

Diarrhea is a rare occurrence. Others can possess the bacterium without becoming ill, but they may still transmit the infection to everyone else. Together with paratyphoid fever, typhoid fever is an enteric fever.

Rheumatic Fever

Rheumatic fever might result in the development of untreated strep throat or scarlet fever illnesses. Strep throat and scarlet fever are caused by bacteria known as group A Streptococcus (group A strep). Rheumatic fever typically occurs 1 to 5 weeks after a case of scarlet fever or strep throat.

Rheumatic fever is believed to be caused by a reaction of the immune system, the body's protective system. The immune system mounts a generalised inflammatory response in reference to the previous strep throat or scarlet fever illness.

Symptoms of Rheumatic Fever have been Mentioned below:

Fever is a term used to describe a state of
Arthritis causes sore, tender joints in the knees, elbows, hips, and wrists.
Congestive heart failure signs include chest pain, chest tightness, and a rapid heartbeat.
Fatigue is a common occurrence.
Chorea is a term for jerky, uncontrollable body movements.
Nodules (painless lumps) below the skin near joints.
Pink rings having a clear core show as a rash.

Viral Fever

A virus induces a higher-than-normal body temperature, which is known as a viral fever. A runny nose, nausea, coughing, exhaustion, and joint pain are some of the symptoms which a person may experience. Although not everyone gets a fever even if they have a virus, it is an indication that perhaps the body is attempting to combat the infection.

Over time and complementary therapies including over-the-counter (OTC) drugs and cold compresses, certain viral illnesses can change. A high body temperature, on the other hand, can necessitate medical attention.

By breathing, sneezing, or contacting objects and people, an infected person may transmit a viral infection. Washing hands regularly and disinfecting surfaces regularly may hopefully maintain these diseases at bay.

Dengue Fever

The dengue virus is responsible for causing dengue fever, a mosquito-borne tropical disease. Three to fourteen days after infection, signs normally emerge. A high fever, nausea, headache, joint and muscle pains, and a distinctive skin rash are all possible symptoms. It usually takes two to seven days to recover.

The disease can progress to serious dengue, often defined as dengue hemorrhagic fever, which causes low blood platelet levels, bleeding, and blood plasma loss, or to dengue shock syndrome, which causes extremely low blood pressure.

Dengue fever is transmitted by female mosquitoes of the Aedes genus, especially Aedes aegypti. The virus comprises five serotypes; infection with one form normally confers lifelong immunity, while infection with the others confers only short-term immunity. Following an infection of a particular form, the threat of serious problems rises. To validate the diagnosis, a variety of treatments are performed, such as detecting antibodies to the virus or its RNA.

Dengue Fever Symptoms

The Dengue fever symptoms may include:-

Tenderness and pain in the stomach.
Vomiting (at least 3 times in 24 hours).
Bleeding from the nose or gums is a common occurrence.
Blood with in stool or vomited blood
Feeling exhausted, irritated, or restless.

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FAQs on Fever: Causes, Types, and Symptoms Explained

1. What exactly is a fever, and why does our body get one?

A fever is a temporary increase in your body temperature, typically above the normal range of 98.6°F (37°C). It's not an illness itself but a sign that your body is fighting one. Your immune system raises the body's temperature as a defence mechanism to make it harder for germs like bacteria and viruses to survive and multiply.

2. What are the most common causes of a fever?

Fevers are most often caused by infections. The main causes include:

Viral infections, such as the common cold, flu, or COVID-19.
Bacterial infections, like strep throat, pneumonia, or urinary tract infections (UTIs).
Inflammatory conditions, like rheumatoid arthritis.
A reaction to some medications or immunisations.

3. Besides a high temperature, what other symptoms often come with a fever?

When you have a fever, you might also experience other symptoms as your body fights off an infection. Common ones include sweating, chills and shivering, headache, muscle aches, loss of appetite, and feeling weak or dehydrated.

4. What temperature is considered a high fever, and when should you see a doctor?

Generally, a temperature above 100.4°F (38°C) is considered a fever. A temperature over 103°F (39.4°C) is often considered a high fever in adults. You should consult a doctor if a fever is very high, lasts more than three days, or is accompanied by severe symptoms like a stiff neck, confusion, or difficulty breathing.

5. How does a higher body temperature actually help fight an infection?

A higher body temperature creates an inhospitable environment for many pathogens. It can slow down the replication of viruses and bacteria. Additionally, a fever stimulates your immune system, increasing the production and activity of white blood cells that are essential for attacking and destroying invading germs.

6. Are all fevers the same, or are there different patterns?

No, fevers can show different patterns, which can sometimes help doctors diagnose the cause. Common patterns include:

Intermittent fever: The temperature is high but returns to normal at least once every 24 hours.
Remittent fever: The temperature fluctuates but always remains above normal.
Continuous fever: The temperature stays elevated with very little change throughout the day.

7. How is treating a fever from a viral infection different from one caused by a bacterial infection?

The main difference lies in the treatment of the underlying cause. For a viral infection like the flu, treatment focuses on managing symptoms with rest, fluids, and over-the-counter fever reducers. For a bacterial infection, a doctor will prescribe antibiotics to kill the specific bacteria causing the fever, in addition to managing the symptoms.

8. Can you explain the difference between fever and hyperthermia?

While both involve a high body temperature, their cause is different. A fever is a controlled increase in the body's temperature set point by the brain's hypothalamus in response to an infection. Hyperthermia, on the other hand, is an uncontrolled increase in body temperature caused by external factors, like heatstroke, where the body absorbs more heat than it can release.