The body temperature refers to the temperature of the viscera and tissues of the body. It is kept within the normal level by maintaining a balance between the heat gain and heat loss, which is regulated by the hypothalamus.

The body temperature is best recorded with a mercury thermometer which should be kept in position for about a minute. Usually temperature is recorded in the axilla. However, if there is a lot of perspiration, oral temperature should be taken. In cholera, rectal temperature is recorded which may be high, whereas the skin temperature may be subnormal.

The normal body temperature varies from 36 degree Celsius – 37.5 degree Celsius. There is normally a diurnal variation of 1 degree Celsius, the lowest temperature being between 2-4 am and highest in the afternoon.

Fever or pyrexia is an increase of more than 1 degree Celsius or any rise above the maximal normal temperature.

Types of Fever

1. Continuous fever: The temperature remains above normal throughout the day and does not fluctuate more than 1 degree Celsius in 24 hours e.g. lobar pneumonia, typhoid, urinary tract infection, infective endocarditis, brucellosis, typhus, etc.
2. Remittent fever: The temperature remains above normal throughout the day and fluctuates more than 2 degree Celsius in 24 hours e.g. typhoid, infective endocarditis, etc. This type of fever is most common in practice.
3. Intermittent fever: The temperature is present only for some hours in a day and remains to normal for the remaining hours. When the spike occurs daily, it is quotidian, when every alternate day, it tertian and when every third day, it is quartan. Intermittent fever is seen in malaria, kala-azar, pyemia, septicemia etc.
4. Hectic or septic: The temperature variation between peak and nadir is very large and exceeds 5 degree Celsius e.g. septicemia.
5. Pel Ebstein type: There is a regular alternation of recurrent bouts of fever and afebrile periods. The temperature may take 3 days to rise, remains high for 3 days and remits in 3 days, followed by apyrexia for 9 days.
6. Low grade fever: Temperature is present daily especially in the evening for several days but does not exceed 37.8 degree Celsius at any time. Usually it does not indicate disease, but it is commonly present with tuberculosis.

Causes of Fever

1. Infection: Bacterial, viral, rickettsial, fungal parasitic, etc.
2. Neoplasms: Fever may be present with any neoplasm but commonly with hypernephroma. Lymphoproliferative malignancies, carcinoma of pancreas, lung and bone and hepatoma.
3. Vascular: Acute myocardial infarction, pulmonary embolism. Pontine hemorrhage, etc.
4. Traumatic: Crush injury
5. Immunological:

• Collagen disease, SLE, rheumatoid arthritis.
• Drug fever
• Serum sickness

6. Endocrine: Thyrotoxicosis, Addison’s disease.

7. Metabolic: Gout, porphyria, acidosis, dehydration

8. Hematological: Acute hemolytic crisis

9. Physical agents: Heat stroke, radiation sickness.

10. Miscellaneous: Factitious fever, habitual hyperpyrexia, cyclic neutropenia

Special Types of Fever

1. Fever with rigors: This occurs in:

• Malaria
• Kala azar
• Filariasis
• Urinary tract infection
• Cholangitis
• Septicemia
• Infective endocarditis

2. Fever with herpes labialis: Elevated body temperature may activate the herpes simplex virus and cause small vesicles around the angle of the mouth (herpes labialis). It occurs with:

• Pneumonia
• Malaria
• Meningitis
• Streptococcal infection

3. Fever with rash: This is seen in:

• Chicken pox
• Small pox
• Measles
• Rubella
• Typhus
• Allergy

4. Fever with membrane in the throat: occurs in:

• Diphtheria
• Infectious mononucleosis
• Agranulocytosis
• Moniliasis
• Vincent’s angima

5. Fever with delirium: This is common in:

• Encephalitis
• Typhoid state
• Meningitis
• Pneumonia (especially in alcoholics and elderly people with senility)

6 Hyperpyrexia
Hyperpyrexia is said to occur when body temperature is more than 105 degree Fahrenheit.

1. Tetanus
2. Malaria
3. Septicemia
4. Heat Stroke
5. Encephalitis
6. Pontine hemorrhage

Benefits of Fever

In some human disease, fever is beneficial, e.g. widespread cancer, neurosyphilis, chronic arthritis, etc. Fever was often induced in these diseases by injection of milk protein or BCG vaccine.

It has been suggested that fever is associated with release of endogenous pyrogens, which activate the T cells and thus enhance the host defense mechanism.

Harmful Effects

1. Hypercatabolism-nitrogen wastage and weight loss.
2. Fluid and electrolyte imbalance-due to sweating.
3. Convulsions and brain damage
4. Circulatory overload, arrhythmia, etc.