BALTIMORE — Could a case of herpes increase your risk for dementia during old age? A team from Johns Hopkins Bloomberg School of Public Health finds that several common infections could negatively impact brain health, especially for middle-aged and older adults. Some of the viruses are actually more common during childhood, while up to 50 percent of the population may carry another one of these parasites.
“The idea that common infections could contribute to cognitive decline and perhaps Alzheimer’s disease risk was once on the fringe and remains controversial, but due to findings like the ones from this study, it’s starting to get more mainstream attention,” says senior author Adam Spira, PhD, professor in the Bloomberg School’s Department of Mental Health and a core faculty member of the Johns Hopkins Center on Aging and Health, in a university release.
The researchers studied the antibody levels to five common pathogens in 575 middle-aged and older adults between the ages of 41 and 97. Four of these were herpes viruses: herpes simplex virus type 1, cytomegalovirus, varicella zoster virus (chickenpox and shingles viruses), and the Epstein-Barr virus. The last one was a parasite called Toxoplasma gondii. The team recruited the participants from the Epidemiologic Catchment Area (ECA) Study, completed in East Baltimore in 1981. These individuals donated blood for testing and took cognitive tests.
“After accounting for participants’ age, sex, race, and the largest genetic risk factor for Alzheimer’s disease, the data in our study showed that a greater number of positive antibody tests related to five different infections was associated with poorer cognitive performance. To our knowledge, this kind of additive effect of multiple infections on performance on a cognitive test has not been shown before,” explains Dr. Spira.
The link is stronger in people without the Alzheimer’s gene
For common pathogens that people often encounter during childhood, the body either clears the illness or it turns into suppressed, latent infection. Therefore, the team considered that high levels of antibodies in these participants point to the infections becoming more active due to their immune systems weakening with age.
Geneticist Brion Maher, PhD, a study co-author and professor in the Bloomberg School’s Department of Mental Health, took things even further. He additionally analyzed the results for participants who had a common Alzheimer’s risk factor, the Ɛ4 variant of the apolipoprotein-E (ApoE) gene. Results show there was an association between positive antibody counts and cognitive status in both Ɛ4 and non-Ɛ4 groups, however it was stronger in the latter.
“That was a surprise, finding a weaker link in the Ɛ4 group,” says Maher. “It’s something that should be followed up with larger studies.”
With the help of funding from the National Institute on Aging, the team is now following up with ECA data in Baltimore from 2016-2022 and collecting additional data from these participants.
The findings are published in the journal Alzheimer’s & Dementia.