TT virus (TTV): the misnamed "hepatitis TT"

The TT virus (Torque teno virus, or TTV) is a very common virus that most healthy people carry in their bodies without knowing it. Despite the name “hepatitis TT” that is sometimes used for it, we now know that it does not cause hepatitis or any known liver disease. If someone mentioned this virus to you, the short answer is reassuring: it is not a condition that needs treatment.

It was discovered in 1998 in a patient who developed hepatitis after a transfusion, and that patient’s initials, TT, ended up naming the virus. In those early years it was suspected of harming the liver, which is why it came to be called “hepatitis TT.” Decades of research have shown that this suspicion does not hold up. To understand what liver inflammation actually is, you can review what is hepatitis?.

What is the TT virus?

The TT virus is a small, non-enveloped virus with a single-stranded DNA genome. It belongs to the Anelloviridae family (the old classification as “Circinoviridae” is no longer used). It is enormously diverse: there are many different genotypes and related viruses, such as the TTV-like minivirus (TLMV) and the SEN virus.

Together, these viruses are one of the most constant components of what is called the human virome, meaning the set of viruses that normally live alongside us without causing disease, much as gut bacteria are part of the normal flora.

How common is it?

Very common. It is detected in a large proportion of healthy people, with figures ranging from 30% to more than 90% depending on the technique and the population studied. The infection is usually persistent: once acquired, the virus tends to stay with the person for years, without causing symptoms.

It spreads easily through several routes (respiratory, digestive, blood) and can also pass from mother to child. That is why it is so widespread in the general population worldwide.

Does it cause hepatitis or liver damage?

No. This is the most important point and the one that has become clearest over time. Although the TT virus is sometimes found in people with liver disease, it is found just as often in completely healthy people. Being infected with the TT virus does not explain cases of hepatitis, and it has not been linked to cirrhosis or liver cancer.

In other words, finding the TT virus on a test does not mean you have a liver disease. Testing for this virus routinely is not part of a liver work-up and has no clinical value for the patient.

So why is it studied today?

Current interest in the TT virus is different from what it was twenty years ago. Because the virus lives permanently in the body, its amount in the blood (the viral load) rises or falls depending on the state of the immune system. When the defenses are more “held back,” the virus multiplies more and its load rises; when the immune system is more active, the load falls.

For this reason it is being evaluated as a marker of immune status, especially in transplant recipients who take medications to prevent rejection of the organ:

• A very high load indicates that the immune system is heavily suppressed, with a greater risk of infection.
• A very low load indicates little immunosuppression, with a greater risk of rejection of the transplanted organ.

The idea is to measure the virus in order to fine-tune the dose of immunosuppressive drugs. This is a promising line of research, still under study, and not a test ordered in routine practice. Here the TT virus is of interest not as a cause of disease, but as a “thermometer” of the immune defenses.

The bottom line for patients

If the TT virus or a “hepatitis TT” was mentioned to you, keep this in mind: it is a nearly ubiquitous, harmless virus that does not damage the liver. It needs no treatment or follow-up. Its only current medical interest is to help, in very specific settings such as transplantation, estimate how active the immune system is.

See also

• What is hepatitis?
• Hepatitis G
• Liver transplant
• Cirrhosis