Researchers here find an association in an older study population between the presence of cytomegalovirus (CMV) - and other common herpesviruses - and the observed degree of cognitive decline. A good deal of evidence from past years supports the theory that CMV accelerates immune system aging, causing the immune system to devote ever more of its limited capacity to uselessly fighting CMV rather than productively carrying out its other tasks. Our immune response is incapable of clearing CMV from the body, and the virus lingers to return in force again and again regardless of the effort devoted to battle it. Since immune failure is a large component of age-related frailty, this is an important topic, and more consideration should be given to approaches that might fix the problem, such as selective destruction of CMV-focused immune cells to free up space for replacement with useful immune cells. As a further consideration, since portions of the immune system serve specialized support roles in brain tissue, it isn't a stretch to think that immune dysfunction may be a contributing cause of cognitive decline in aging.
Certain chronic viral infections could contribute to subtle cognitive deterioration in apparently healthy older adults. Many cross-sectional studies, which capture information from a single time point, have suggested a link between exposure to cytomegalovirus (CMV) and herpes simplex viruses (HSV) 1 and 2, as well as the protozoa Toxoplasma gondii and decreased cognitive functioning. "Our study is one of the few to assess viral exposure and cognitive functioning measures over a period of time in a group of older adults. It's possible that these viruses, which can linger in the body long after acute infection, are triggering some neurotoxic effects."
The researchers looked for signs of viral exposures in blood samples that were collected during the Monongahela-Youghiogheny Healthy Aging Team (MYHAT) study, in which more than 1,000 participants 65 years and older were evaluated annually for five years to investigate cognitive change over time. They found CMV, HSV-2 or toxoplasma exposure is associated with different aspects of cognitive decline in older people that could help explain what is often considered to be age-related decline. "This is important from a public health perspective, as these infections are very common and several options for prevention and treatment are available. As we learn more about the role that infectious agents play in the brain, we might develop new prevention strategies for cognitive impairment." Now, the researchers are trying to determine if there are subgroups of people whose brains are more vulnerable to the effects of chronic viral infection.