Epidemiological evidence of herpes involvement in dementia continues to accrue. The latest finding comes from a Swedish cohort of 530,000 people, all over 50 years old. In the February 14 Alzheimer’s & Dementia, researchers led by Hugo Lövheim, Umeå University, reported that untreated herpes infection upped long-term dementia risk 1.5-fold, and antiviral treatment lowered risk by 11 percent. This is consistent with previous findings in Asian and European cohorts.
Whether herpes virus infection can contribute to AD has been hotly contested. Nationwide epidemiological studies have been gaining steam in the past few years, offering real-world evidence of a potential link. In Taiwan, people with severe herpes or shingles had a 2.5-3 times higher risk of dementia; antiviral treatment substantially reduced risk (Tsai et al., 2017; Chen et al., 2018; Tzeng et al., 2018). In South Korea, a shingles diagnosis came with a 12 percent higher risk of dementia; antivirals reduced risk somewhat (Bae et al., 2020). In Germany, untreated herpes infections increased dementia risk by 18 percent and in Denmark and Wales, antiherpetics reduced dementia risk by up to 11 percent (Jan 2021 news).
Now, first author Karin Lopatko Lindman and colleagues searched through two national Swedish health registries: the National Patient Register and the Swedish Prescribed Drug Register. Both include data on age, sex, geographical information, as well as dates of hospital admission/discharge, and prescription. The scientists identified 265,172 people who were either diagnosed with shingles or herpes simplex virus (HSV) infection or were prescribed antiherpetic drugs between 2005 and 2017. Of those, 9,933 had untreated herpes or shingles, 29,593 had been treated for same, and 225,646 were prescribed antiherpetics without a confirmed diagnosis. Of those who were prescribed antiherpetics, more than 92 percent received a single prescription and more than 95 percent received either acyclovir or valacyclovir for seven days. The researchers assigned an age- and sex-matched control to each case.
Those with untreated herpes infections were 1.5-times more likely to develop any-cause dementia than controls. People diagnosed with herpes who took antivirals had a 25 percent reduced dementia risk compared to those who did not take antivirals, whereas anyone who took antiherpetics, regardless of official herpes diagnosis, had an 11 percent reduced risk compared to those who did not take them.
Earlier this month, Lövheim was one of eight people who won an award from ALZgerm for his hypothesis on Herpes infection as a cause of Alzheimer’s (Feb 2021 news). Lövheim is also conducting a Phase 2 trial in Sweden testing the effect of four weeks of daily valacyclovir on cognitive decline and biomarkers in people with AD. He told Alzforum that results should be published in the upcoming months.—Chelsea Weidman Burke
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- Chen VC, Wu SI, Huang KY, Yang YH, Kuo TY, Liang HY, Huang KL, Gossop M. Herpes Zoster and Dementia: A Nationwide Population-Based Cohort Study. J Clin Psychiatry. 2018 Jan/Feb;79(1) PubMed.
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- Bae S, Yun SC, Kim MC, Yoon W, Lim JS, Lee SO, Choi SH, Kim YS, Woo JH, Kim SY, Kim SH. Association of herpes zoster with dementia and effect of antiviral therapy on dementia: a population-based cohort study. Eur Arch Psychiatry Clin Neurosci. 2020 Jul 1; PubMed.
No Available Further Reading
- Lopatko Lindman K, Hemmingsson ES, Weidung B, Brännström J, Josefsson M, Olsson J, Elgh F, Nordström P, Lövheim H. Herpesvirus infections, antiviral treatment, and the risk of dementia-a registry-based cohort study in Sweden. Alzheimers Dement (N Y). 2021;7(1):e12119. Epub 2021 Feb 14 PubMed.