You're depressed? Maybe you should get vaccinated!

What if depression is a response to infection? Turhan Canli, a professor of integrative neuroscience at Stony Brook University,

was intrigued by research showing a connection between depression and inflammation in the body, and he started to think about the known causes of inflammation — among them pathogens like bacteria, viruses and parasites.

He notes that the symptoms of depression are similar to those of infection: “Patients experience loss of energy; they commonly have difficulty getting out of bed and lose interest in the world around them. Although our Western conceptualization puts affective symptoms front-and-center, non-Western patients who meet DSM criteria for major depression report primarily somatic symptoms.”

And, he writes, we already know that infectious agents can affect our emotions — he points to Toxoplasma gondii, a parasite that’s now somewhat famous (at least among science lovers) for its striking impact on its hosts. T. gondii can make rats like the scent of cat urine (causing obvious problems for the rats). In humans, it may have serious psychological effects — Dr. Canli cites research linking T. gondii with suicide. “Yet,” he writes, “large-scale studies of major depression and T. gondii or systematic searches to discover other potential parasitic infections have not yet been conducted.”

He believes researchers should compare tissue samples from depressed patients with those from non-depressed people, looking for evidence both of known pathogens and of new ones.

If successful, such a search could bring about big changes in depression treatment. “Imagine if we had identified one or multiple pathogens that all are associated with major depression,” Dr. Canli said. “That could mean that at some point in the future a patient would present himself or herself at the doctor’s office and the first thing they would do is run a workup on the blood or stool sample to identify exactly which particular pathogens might be present, and then develop a very targeted treatment program to address exactly those.”

One day, he suggests in his paper, research into infection and depression could even lead to a vaccine.

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