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Function of Fever

What is the function of fever in disease? When researcher Matthew Kluger infected a group of desert lizards with bacteria, he found that raising their body temperature to achieve a fever improved their chances of survival. Because reptiles are cold-blooded, Kluger used sunlamps to raise the lizards' body heat, speeding up their bodies' defenses. Did fever evolve in part to help organisms survive infection?

Credits: From "La Fièvre" by Matthew J. Kluger, La Recherche 12: 688-696, 1981.

Function of Fever

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Function of Fever:

When a child or parent becomes feverish with shivers, chills, and sweats, our first thought is to get the temperature down. Pharmacies sell billions of fever-reducing pills like aspirin and acetaminophen every year, and schools often insist that students stay home until their fever is gone.

But is this "fever phobia" backed up by science?

Increasingly, medical researchers are discovering that fever has endured in mammals and other creatures for good reasons, though the reasons why are not clear. Often, a fever in response to an infection is actually a reflection of the body's defenses going into high gear. Some parts of the immune system work better at a higher temperature, which strengthens resistance to infection and increases the odds of survival.

The new thinking is that mild fever can be a positive adaptation and shouldn't necessarily be treated. At other times, though, fever may spur the microbes' growth rate by raising the temperature of the host body. In this case, the attackers have evolved a way to chemically manipulate the host's immune system for their own advantage. And a high fever is a danger sign, especially in young children.

What is this mysterious phenomenon, fever? It's not simply a rise in body temperature. It is an upward shift in the body's "set point," or core temperature, which is regulated by the hypothalamus in the brain. In response to an infection, the body releases chemicals that cause a sensation of being cold. The hypothalamus then raises the set point by making the body burn fat, reduce blood flow to the skin, and shiver.

Most of the time, fever isn't dangerous in itself, but a patient will feel more comfortable at a lower temperature. In a dramatic demonstration of fever's benefits, researcher Matthew Kluger infected desert iguanas with bacteria.

Because these lizards are cold-blooded, they could only warm their bodies by seeking outside heat -- in this case, sunlamps. All except one of 13 iguanas sought the warmth to raise their temperatures, and those 12 survived; the other one died.

After that, Kluger injected 12 other iguanas with live bacteria, and also gave them a fever-fighting drug. Five of them failed to develop a fever, and died as a result. The other seven, which somehow became feverish despite the drug, survived.

Despite experiments like this, scientists haven't yet answered all their questions about this common and ancient body symptom.

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