Sickness behavior

Sickness behavior is a coordinated set of adaptive behavioral changes that develop in ill individuals during the course of an infection. These changes usually include lethargy, depression, anxiety, loss of appetite, sleepiness, hyperalgesia, reduction in grooming and failure to concentrate. Sickness behavior is a motivational state that reorganizes the organism's priorities to cope with infectious pathogens. It has been suggested as relevant to understanding depression, and some aspects of the suffering that occurs in cancer.

Overview

Sickness behavior is a highly organized strategy that mammals use to fight infection. It is driven by the pro-inflammatory cytokines produced by the immune system of the sick animal, for example IL-1, IL-6 and TNF. These cytokines are produced by activated macrophages and other cells of the immune system, in response to lipopolysaccharides (LPS) present on the cell wall of gram-negative bacteria. Cytokines are produced locally in the brain in response to peripheral infections, but they can also reach the brain directly, through the circumventricular organs, or indirectly, by inducing the production of other cytokines in the endothelial cells of the brain blood vessels.

Symptoms

The symptoms of sickness behavior include:

• Lethargy
• Depression
• Anxiety
• Loss of appetite
• Sleepiness
• Hyperalgesia
• Reduction in grooming
• Failure to concentrate

Relevance to Other Conditions

Sickness behavior has been suggested as relevant to understanding depression, and some aspects of the suffering that occurs in cancer. It has also been suggested that sickness behavior is a good model for understanding some aspects of chronic fatigue syndrome and fibromyalgia.

See Also

• Cytokines
• Inflammation
• Psychoneuroimmunology

References

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  Michael Ancher 001