Herpes increases the risk of mental disorders and suicidal behaviour

Diet and lifestyle 29. sep 2019 3 min Postdoc Janna Nissen Written by Kristian Sjøgren

New Danish research shows that herpesvirus not only causes cold sores but also increases the risk of developing a mental disorder and attempting or dying from suicide. The discovery may be important in understanding how mental disorders develop.

People who have herpes do not just risk getting cold sores when they are stressed or have a cold. New Danish research using data from the Danish Blood Donor Study indicates that being infected with herpes simplex type 1 virus increases the risk of developing a mental disorder and of attempting or dying from suicide.

The results show that Danish blood donors who had herpes had a 1.40 times higher risk of attempting or dying from suicide than a matching control group. Similarly, the risk of developing a mental disorder later in life was 1.44 times higher among blood donors who had herpes at the time they donated blood.

“The unique aspect of our study is that we can definitely conclude that these people were infected with herpes before they developed a mental disorder. It is often unknown whether people were infected before or after being diagnosed with a mental disorder, but we could determine this in our study, in which we discovered an association between having herpes and having an increased risk of developing a mental disorder later in life,” explains a researcher behind the study, Janna Nissen, Postdoctoral Fellow, Biobank Unit, Department of Clinical Immunology, Rigshospitalet, Copenhagen.

The research results were recently published in Psychoneuroendocrinology.

82,000 Danes studied

The researchers used data from the Danish Blood Donor Study and matched them with data from other patient registries to identify the blood donors who either had or later developed a mental disorder, attempted suicide or died from it.

The Danish Blood Donor Study contains blood samples from 81,912 residents of Denmark, and in collaboration with researchers from the Stanley Division of Developmental Virology, Johns Hopkins University School of Medicine, Baltimore, MD, USA, the Danish researchers analysed the blood samples for herpesvirus and other markers of infection.

The researchers linked this with records in patient registries and found 1504 people with a diagnosed mental disorder and 353 people who had attempted or died from suicide.

The study is the first suggesting that herpes may be associated with attempting or dying from suicide.

“Being able to examine the time perspective here and determine that the risk of developing a mental disorder increases after a person has been infected with herpes is very interesting. The fact that we can see that they were infected before the risk of mental disorder increased is unique and indicates an association,” says Janna Nissen.

Herpes infects the brain

According to Janna Nissen, the association between herpes, mental disorder and the risk of suicidal behaviour is presumably related to how the herpesvirus infects the body.

People infected with herpes have the virus permanently; it erupts when the immune system is suppressed, such as when people experience stress, when many people with herpes get cold sores.

Herpes probably not only erupts as cold sores around the mouth but also, among some people, as “cold sores" in the brain. These can potentially affect the state of mind of the person with herpes.

“This happens with other types of infection, such as people who develop toxoplasmosis caused by Toxoplasma gondii, which can also affect their mental state. Some people’s immune system probably keeps herpes under control, and then it never manifests as anything but an occasional cold sore, whereas other people may be quite affected mentally because their immune system does not suppress the infection,” explains Janna Nissen.

In general, strong scientific evidence indicates that some chronic infections are associated with various types of mental disorders.

Can treating herpes more rapidly avoid mental disorders?

These new results are the first step towards new understanding of how chronic infections by common viruses can strongly affect the people who are infected.

Janna Nissen imagines that future research confirming this will provide an incentive to more closely assess the treatment of people with herpes, who may need to be treated much earlier and more intensively than they are today.

In addition, the study may also be useful to make researchers aware of the molecular mechanisms underlying the development of mental disorders.

”We may conclude that it could be worthwhile to try to treat people with herpes early before the virus damages the brain, potentially resulting in a mental disorder,” says Janna Nissen.

Determining the role of the immune system in developing mental disorders

The future work of the research group will examine the interaction between humans, viruses, the brain and mental disorders.

The researchers would like to investigate various biomarkers among people with herpes. They would aim to find the molecular causes for why some people with herpes have an increased risk of developing a mental disorder and others do not.

The Danish Blood Donor Study has stored blood samples from all previous blood donations in Denmark, and thus the researchers can go back in time and examine the blood for various biomarkers.

“Maybe it all depends on the immune system, which suppresses the virus for some people but not for others. We hope that our discoveries can be part of understanding the mechanisms of mental disorders,” says Janna Nissen.

Herpes simplex virus type 1 infection is associated with suicidal behavior and first registered psychiatric diagnosis in a healthy population” has been published in Psychoneuroendocrinology. Several authors are employed at the Novo Nordisk Foundation Center for Protein Research, University of Copenhagen.

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