Photo/Illutration The human herpes virus type 6 (HHV6) (Provided by Jikei University School of Medicine professor Kazuhiro Kondo)

 

A Japanese research team found that an infection with a particular virus during infancy may be a trigger for depression in later life.

The team from the Jikei University School of Medicine in Tokyo discovered the possibility though inherited genes have long been thought to be likely causes behind depression.

The team’s findings were published in a U.S. science journal in February.

The team announced in 2020 that SITH1 proteins, which are produced by the human herpes virus type 6 (HHV6), play a role in developing depression.

HHV6 is the virus that causes exanthema subitum, a condition characterized by a fever that lasts about three days. Almost everyone is infected during infancy and carry the latent virus through life.

When a person with the virus feels run down, HHV6 becomes present in saliva. The virus spreads from the mouth to the nose and then to the brain, causing reinfection and producing SITH1 proteins.

Those who have SITH1 proteins are more prone to developing depression than those who don’t, the research team members said.

The team also determined through experiments involving mice that reinfection brain cells, uncovering a part of the mechanism of how depression develops.

For the latest study, the team conducted a detailed examination of the genes of the virus that produces SITH1 and found that it can be classified into two types: one that can produce this protein with ease and another that does so with difficulty.

The researchers found that 68 percent of 28 patients with depression were infected with a type that can easily produce SITH1.

However, 29 percent of 35 healthy people were infected with the same type of the virus.

Of the patients with depression infected with the type that can easily produce the protein, 47 percent had family members dealing with depression.

HHV6 is mainly transmitted from mothers to infants.

Although it has been believed that genetic factors are associated with depression, there had been no reports on genes closely related to the issue of mental health.

The latest findings showed a possibility that the virus transmitted from the mother makes the child prone to depression, not the mother’s genes.

“When we uncover the mechanism, we can also find solutions,” said Kazuhiro Kondo, a professor of viruses who is a member of the team.

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