The herpes virus can hide in the brain undetected

Submitted on Thu, 11/03/2016 - 14:22

Human brain tissue may contain the herpes simplex virus (HSV) without causing any symptoms, a new study at the University of Tampere shows. The purpose of the study was to shed light on the mechanisms causing Alzheimer’s disease (AD).

Herpes simplex virus type 1 causes cold sores on the lips and face, is very common and affects most people. HSV type 2 predominantly affects the genital area and is one of the most common sexually transmitted infections. The virus remains latent in neuronal cells and reactivates due to stress, illness and other unknown factors. Rare but life-threatening brain infections caused by the virus have also been described. Recent research has suggested that latent HSV in the central nervous system is related to the aetiology of AD, which causes dementia.

The research conducted at the Universities of Tampere, Finland and Umeå, Sweden investigated the prevalence of type 1 and 2 HSV in the brain tissue samples from the Tampere Autopsy Study (TASTY) by copying the DNA sequences of the virus. The same patients’ blood samples were investigated for HSV antibodies in order to confirm whether they had contracted the virus. The study analysed whether the virus prevalent in the brain tissue and the presence of HSV antibodies were associated with the neuropathological changes of AD in the same individuals.

The research data came from a cohort of 603 men and women, average age 63 years, who underwent an autopsy at the Department of Forensic Medicine, University of Tampere. The sample represents community-dwelling individuals who are primarily free from dementia. The same research group at the University of Tampere has previously established that the neuropathological changes of AD start already around age 30 and that they are present in nearly 100 percent of the oldest cohorts even though the presence of dementia in the TASTY sample is rare. The neuropathological changes associated with AD do not directly predict the severity of the symptoms of dementia.

HSV was shown to be present in human brain tissue in 11 (1.9%) of the 584 samples analysed in the TASTY cohort, of which six had Alzheimer’s disease neuropathological amyloid beta (Aβ) even though most of the samples containing Aβ did not test positive for HSV. The research provides epidemiological evidence that HSV can be present in the brain tissue of at least 1.9 percent of the population without causing encephalitis.

“The connection between HSV and Alzheimer’s disease dementia still remains unclear. We do not know why HSV is present in some peoples’ brain and not in others, and this will be the main focus of our further studies,” says postdoctoral researcher Eloise Mikkonen from the University of Tampere.

The research article:
Olsson Jan, Lövheim Hugo, Honkala Emma, Karhunen Pekka, Elgh Fredrik, Kok Eloise (2016).
HSV presence in brains of individuals without dementia: the TASTY brain series. Disease Models and Mechanisms

For more information, please contact:
Postdoctoral researcher Eloise Mikkonen, tel. +358 442 936 236,