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How infections can affect mental health

Amanda Simanek, an assistant professor of epidemiology in the Joseph J. Zilber School of Public Health, recently led a series of studies examining the links between infection and mood disorders.

Simanek’s three studies zeroed in on persistent pathogens – the kind that, once acquired, can result in chronic infections, some of which stay with a person for life. Examples include the herpes family of viruses and Helicobacter pylori, the bacterium that causes stomach ulcers. She found an association between such infections and a greater likelihood of depression. In some cases, the effects were stronger among women.

Broader research in the area has looked at such connections, but Simanek’s research plowed new ground and added important context to prior studies. Hers were the first longitudinal studies of these relationships and the first to explore whether gender differences played a role. Moreover, while much of the existing studies included older populations, Simanek was among the first to examine these associations in younger people.

Amanda Simanek
Amanda Simanek

Also, previous researchers have hypothesized that inflammation is a key biological mechanism by which a persistent infection helps trigger depression. Simanek’s studies were among the few to test this hypothesis. “We did not find support for the role of inflammation,” Simanek says, “which suggests additional pathways linking persistent pathogens to mood disorders should be investigated.”

Data sources for her studies included the publicly available National Health and Nutrition Examination Survey, conducted by the federal Centers for Disease Control and Prevention. Simanek also used data from studies of middle-aged and older adults in Detroit and Sacramento, California, that were previously conducted by research colleagues.

Across two of the studies, Simanek found a consistent association between adults infected with cytomegalovirus – a type of herpes virus – and the new onset of depression among middle-aged and older adults. A third study also revealed that women ages 15 to 39 who’d been exposed to Helicobacter pylori had 2.5 times higher odds of a history of low-grade depressive symptoms when compared to women who hadn’t been exposed. The opposite association was observed in young men.

Simanek wants to build on this work by continuing a broader examination of the relationship between health and socioeconomic status. People who live in poverty acquire persistent pathogens earlier in life and at a higher rate, which, Simanek hypothesizes, could help explain social disparities in mental health. Funded by a $450,000 grant from the National Institute on Minority Health and Health Disparities, she’ll explore how socioeconomic status helps shape immune function at birth.