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Infections Can Trigger Mental Disorders, Researchers Say

Infections Can Trigger Mental Disorders, Researchers SayInfection is the general term used to describe the unwanted presence of microorganisms such as viruses, bacteria, parasites, or fungi in the human body. Some infections pose only minor threats to a person’s health and well-being, while others can easily cause severe illness or death. According to the results of a large-scale study published in June 2013 in JAMA Psychiatry, the presence of a significant infection also apparently increases a person’s chances of eventually developing any one of a range of mental health conditions known collectively as mood disorders.

Infection Basics

A variety of viruses, bacteria, parasites and fungi occur naturally in or on the human body, or in environments created by human societies. As a rule, several biological systems within each individual take measures to exclude harmful forms of these microorganisms, and thereby protect health and well-being. Infections occur when one or more these systems fails and harmful microorganisms gain a foothold in the body. The specific symptoms of an infection depend upon the nature of the responsible virus, bacterium, parasite or fungus, as well as the infection’s location. However, generally speaking, reliable indications of infectious processes include a high body temperature (i.e., fever), aching muscles, an unusual loss of energy, and a decline in normal appetite. Certain infection-related symptoms point to a need for some sort of medical care, including a fever accompanied by an extreme headache, a fever accompanied by seizures, persistent coughing, breathing difficulties, the onset of skin swelling, and the onset of a rash.

Certain types of infection in the body can ultimately produce harmful results inside the brain. This situation occurs when the presence of an infectious microorganism leads to some sort of failure in the blood-brain barrier. Normally, this barrier—which contains a network of specialized blood vessel cells—helps limit the types of substances that can pass to the brain from the bloodstream. However, damage in the blood-brain barrier can lead to abnormal penetration of the brain by unwanted microorganisms or materials. Some autoimmune diseases can also damage the barrier and leave the brain unusually exposed to invaders.

Mood Disorder Basics

Mood disorder is the unofficial, blanket term for various forms of depressive illness and various forms of bipolar disorder. Mental health professionals group these conditions together because they all feature primary symptoms centered on unusual shifts away from a normal range of everyday moods and emotions. Depressive illnesses in the mood disorder category include major depressive disorder (i.e., major depression), persistent depressive disorder (formerly known as dysthymia or dysthymic disorder), premenstrual dysphoric disorder, disruptive mood regulation disorder, and “other” specified depressive disorder. Bipolar-related illnesses in the category include bipolar I disorder, bipolar II disorder, cyclothymic disorder (cyclothymia), and “other” specified bipolar and related disorder.

Infection’s Effects

In the study published in JAMA Psychiatry, a team of American and Danish researchers examined the connection between infection and mood disorder risks in more than 3 million Danish citizens over a period of three decades. Roughly 32 percent of these participants developed an infection serious enough to require medical attention during the study. In addition, another 5 percent developed some sort of autoimmune disorder that required medical attention. Of the study participants, 91,637 sought treatment for either a depressive mood disorder or a bipolar mood disorder.

After analyzing their findings, the study’s authors concluded that people who develop medically significant infections experience a roughly 62 percent increase in their likelihood of developing a mood disorder at some point in the future. People who develop autoimmune conditions also acquire increased mood disorder risks. The authors of the study believe that immune system malfunction forms the connection between mood disorders and infectious diseases. Apparently, this malfunction occurs when infectious microorganisms damage the blood-brain barrier and leave the brain more susceptible to infection-related changes normally confined to the rest of the body.


The authors of the study in JAMA Psychiatry consider their findings accurate but preliminary, and point to a need for further research on the topic. Ultimately, they believe that increased understanding of the links between infection, the blood-brain barrier, immune system function, and mood disorders will lead to an improved ability to prevent the occurrence of both depression and bipolar disorder. They also believe that an increased understanding of these connections will lead to improved treatment of existing mood disorder cases.

Posted on August 8th, 2013

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