The Human herpes virus 6, short HHV-6 called, belongs to the family of herpes viruses, which are divided into an alpha, beta and gamma subfamily. HHV-6 belongs to the subfamily of beta herpes viruses, which have a very narrow host range and only reproduce slowly in the body. The virus can cause various diseases in humans, but it can persist in the body without any symptoms.
What is Human Herpes Virus 6?
A total of eight human pathogenic herpes viruses that can cause diseases in humans have been characterized so far. HHV-6 has two subtypes, subtype A and subtype B. The virus was discovered in 1986 and is a DNA double-stranded virus. HHV-6 infects CD4-positive T lymphocytes, specific cells of the human immune system.
The virus spreads through saliva and droplet infection. HHV-6 is distributed worldwide and is very common: more than 90% of adults carry the virus. The infection usually occurs from the sixth month of life in infancy or early childhood. Before the age of six months, the infants are protected against infection by the maternal antibodies that they absorbed through the placenta before birth.
Between the ages of two and five, around 80% of children are infected with the virus. If a pregnant woman becomes infected with HHV-6 for the first time, it can be transmitted to the embryo, so that the child carries the virus in itself at birth.
Meaning & function
Infection with the human herpes virus 6 usually proceeds without clinical symptoms after the initial infection. HHV-6 remains latent in the body, which is a characteristic of all herpes viruses. Most adults are therefore usually unaware that they are infected with the virus.
Complete elimination is usually not possible. The first time the virus is infected, it can be detected in the blood, saliva and stool in the laboratory. Disease of the lymphatic system and the central nervous system occurs. Since the virus can spread along the nerve fibers and thus bypass the blood-brain barrier, it reaches the spinal cord and brain.
Here it infects glial cells and neurons. In the latent phase, HHV-6 is found in the salivary glands, through which it is excreted and spread. At this stage the virus does not produce any particles that are infectious to the body. However, it can be reactivated and re-enter the infection cycle. This can especially happen with a weakened immune system. For example, immunosuppressed patients who have an HIV infection or whose immune system is suppressed as a result of a transplant may experience an increase in virus replication.
If the virus is reactivated, this can manifest itself in the recurrence of the same or similar symptoms as with the initial infection. HHV-6 has various pathogenic mechanisms: The virus can lead to degenerative changes in the cell morphology in infected cells (cytopathic effect). It can induce so-called cytokines, certain proteins that are responsible for the growth and differentiation of cells. HHV-6 can affect immune function by partially suppressing it. The virus can also transactivate other viruses in the event of co-infection.
Illnesses & ailments
The human herpes virus 6 is primarily known as the causative agent of three-day fever. This mostly occurs in early childhood. After several days with a high fever, a characteristic rash develops as the fever subsides.
The three-day fever heals by itself and is rarely associated with complications, so that therapy is usually not necessary. In Europe, it is mostly triggered by subtype B of HHV-6. In individual cases, the disease can also occur in adults and manifests itself in flu-like symptoms. In rare cases, complications with diarrhea and vomiting can occur. In addition, the eyelids and lymph nodes on the neck can swell, papules on the roof of the mouth and uvula can occur and febrile seizures can occur.
Various other diseases suspected to be associated with HHV-6 infection have also been observed in very rare cases. HHV-6 can trigger a chronic fatigue syndrome that is associated with severe fatigue and exhaustion as well as depression. However, this probably affects less than 1% of all HHV-6 infected people. Myocarditis, pneumonia, or hepatitis are also possible.
Conditions such as meningitis and encephalitis have also been observed. HHV-6 could influence the development of multiple sclerosis among other factors. Researchers also suspect that HHV-6, as an additional factor, can promote the development of basal cell carcinoma and squamous cell carcinoma. If severe complications arise from HHV-6, antiviral therapy can be carried out.