HSV-2, CMV and Toxoplasma gondii...but not HSV-1.
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.