Fever, also known as pyrexia, is the rise in the body’s temperature, as measured in the mouth, above 37° C (98.6° F). Fever is a symptom of many disorders, such as infection by a virus or a bacterium, and it is not itself a disease. The term fever is also used to name certain diseases, such as relapsing fever, rheumatic fever, scarlet fever, undulant fever, and yellow fever, in which high fever is a major symptom. The first signs of fever may be chilly sensations, with associated periods of flushed or warm feelings. The temperature may rise slowly or rapidly and may fluctuate. A rise in temperature may be accompanied by shaking chills. A falling temperature may bring on heavy sweating.
Although people have survived temperatures over 43° C (110°
F), a fever higher than 41° C (106° F) typically results in convulsions,
particularly in babies or the elderly.
The normal healthy body constantly produces heat as cells
burn food for energy. At the same time, the body loses heat through the skin
and through breathing. The temperature of the body is a measure of the balance
between heat produced and heat lost. Under normal circumstances the heat
produced is balanced by the heat lost, keeping the body temperature at the best
level for the cells to carry out their chemical processes. This system of
temperature regulation can be upset by bacterial or viral infections, such as
tonsilitis or influenza. In these cases, proteins called pyrogens are released
when the white blood cells of the body’s defense system fight the
microorganisms responsible for the illness. In some cases the pyrogens are
released by the microorganisms themselves. The pyrogens act on the
hypothalamus, a small area of the brain that functions as a thermometer, causing
it to raise the body’s temperature. While the temperature is rising, the tiny
vessels supplying the skin with blood can narrow, sharply reducing sweating,
which is a way for body heat to escape. The body will thus produce more heat
than it can lose, and fever will result. At the same time, this mechanism helps
the body to fight off infection, and in some cases a very high fever may
actually kill the bacteria causing the infection.
Fever can be reproduced artificially to relieve the symptoms
of such diseases as arthritis and various brain and skin disorders. Artificial
fever was once used for the treatment of syphilis, a sexually transmitted
disease. In 1917 the Austrian neurologist and psychiatrist Julius Wagner von
Jauregg observed that patients suffering from this disease were greatly
improved after an attack of malaria, which had caused high fever. Malarial
fever was used in the treatment of syphilis until the discovery of penicillin.
Although fever is basically a protective mechanism, it often
produces weakness and fatigue. During a fever the body loses large amounts of
salts and water through sweating, and the patient’s desire for food or water is
greatly reduced. Prolonged fever may result in the destruction of body protein
and fat, which can lead to serious weight loss.
Fever is generally treated by lowering the body’s
temperature with aspirin, and by applying cool compresses or alcohol sponges.
To replace the fluids lost from the body by sweating, patients are usually
given large quantities of liquids to drink. In the case of very high fever,
cold baths and ice packs on the body can be effective. (Encarta Encyclopedia)