Worldwide, an estimated 417 million people under the age of 50 have the type of herpes simplex virus typically associated with genital herpes. Given that this is a significant chunk of the world's population, it would be disquieting if the virus was linked to something more nefarious. Prepare to be disquieted: a new study finds that certain chronic viral infections - including the herpes simplex virus - may contribute to cognitive decline in healthy older adults.
The study, published in the journal Alzheimer's Disease and Associated Disorders, is led by Dr. Vishwajit Nimgaonkar, of the University of Pittsburgh School of Medicine in Pennsylvania. The Centers for Disease Control and Prevention (CDC) define cognition as a "combination of mental processes that includes the ability to learn new things, intuition, judgment, language and remembering." When someone experiences cognitive impairment, they have trouble with these processes, affecting their everyday life. For example, they may be unable to care for themselves or carry out everyday tasks, such as preparing their own meals or managing their money. And when an individual has cognitive decline or dementia, their ability to effectively manage medications and existing medical conditions becomes a concern. Needless to say, as our population begins to age, understanding cognitive decline risk factors becomes a public health concern.
'These infections are common,' so this is a public health concern
Dr. Nimgaonkar and colleagues say that previous cross-sectional studies (studies that look at data from a single time point) have found a link between exposure to certain viruses and decreased cognitive functioning.
These viruses include: cytomegalovirus (CMV), herpes simplex virus 2 (HSV) and the protozoa Toxoplasma gondii, which many people are familiar as the parasite found in cat feces.
"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," Dr. Nimgaonkar says. He adds that it is possible that these viruses "are triggering some neurotoxic effects."
To further investigate, the researchers used the Monongahela-Youghiogheny Healthy Aging Team (MYHAT) study, which involved over 1,000 adults over the age of 65 years who were evaluated annually for 5 years to detect any cognitive change. After looking for signs of viral exposures in blood samples, the researchers found that exposure to CMV, HSV-2 or toxoplasma is linked with aspects of cognitive decline typically considered to be age-related decline.
HSV-1 not linked to cognitive decline
Although the results give us cause for concern, there is some good news in the findings: HSV-1, which is the type of herpes associated with cold sores - and which an estimated 3.7 billion people under the age of 50 have worldwide - is not associated with greater temporal cognitive decline. The researchers do note that their findings are independent of general age-related variables, so the link between CMV, HSV-2 and toxoplasma exposure and cognitive deterioration is significant.
For future study, they are aiming to determine if there are subgroups of people who are more vulnerable to the effects of these chronic viral infections. HSV spreads through direct contact, and some people have no symptoms, which means they may be at risk without knowing. Medical News Today recently reported on a study that suggested Alzheimer's-related brain changes occur 2 decades before symptom onset, a finding that could lead to early interventions to stop disease development.