As depression cases rise, doctors try to better understand the phenomenon

By Mark Huffman

What makes someone depressed? The question becomes more urgent as the number of cases of clinical depression increases.

The Centers for Disease Control and Prevention (CDC) estimates depression at some point affects about 9% of U.S. adults, leaving them with feelings of hopelessness, despondency, and sometimes guilt. The agency says major depression is the leading cause of disability for Americans between the ages of 15 and 44.

Researchers have turned out study after study trying to better understand the condition. At the University of Washington a recent study suggested stress is a major trigger.

A recent British study found over-achievers are more at risk of depression, because they become addicted to the Internet. Companies fail to notice the depression, the researchers conclude, because the sufferers are all successful.

Since many of the cases of depression have appeared in the wake of the financial crisis, some researchers looked for – and found – a link to long-term unemployment. Nearly 1 in 5 Americans who have been unemployed for a year or more say they currently have or are being treated for depression.

Physical illness

Here’s a new theory. Major depressive disorder (MDD) is actually an infectious disease and not always caused by external influences.

Turhan Canli, a psychology professor at Stony Brook University, suggests that major depression may result from parasitic, bacterial, or viral infection. He thinks depression needs to be reclassified from a mental illness to a physical one while research continues into its causes.

“Future research should conduct a concerted effort search of parasites, bacteria, or viruses that may play a causal role in the etiology of MDD,” he said.

Canli offers 3 arguments why reconceptualizing MDD as an infectious disease may pay off.

For starters, patients with MDD exhibit physical symptoms like a loss of energy. Beyond that, inflammatory biomarkers associated with depression also suggest an illness-related origin.

Viruses can alter behavior

Canli says there is plenty of evidence that parasites, bacteria and viruses that infect humans can alter their emotional behavior. Finally, he cites the concept of the human body as an ecosystem for microorganisms and the role of genetics.

There’s enough there, says Canli, to justify large-scale studies with depressed patients to see if there actually is a causal relationship between infectious disease and depression. A Northwestern University study, published in September, just might provide some ammunition.

Researchers developed a blood test that measures the levels of 9 RNA blood markers which seem to be different in patients diagnosed with clinical depression, suggesting some kind of physical link.

Depression symptoms

The CDC says symptoms of depression can range from a sad mood and diminished interest in activities to dramatic weight gain or loss, fatigue and excessive and unjustified feelings of guilt.

The condition also poses a substantial burden to the sufferer and friends and family. Interpersonal relationships are particularly likely to suffer when someone is depressed and the CDC says data suggest that few families or networks of friends are likely to remain unaffected.

When major depression goes unrecognized and untreated the results can turn tragic. Consequences can range from ruined marriages to damaged careers to suicide.

The CDC says this disorder is still misconstrued as a sign of weakness rather than being recognized as an illness.