Why virus D worsens the course of chronic hepatitis B

Hepatitis D: why this infection differs from other viral hepatitides

Hepatitis D has a special place among viral liver diseases. Unlike hepatitis A, B, C or E, the hepatitis D virus cannot fully exist on its own. For its replication, it needs the hepatitis B virus, more precisely the surface antigen HBsAg, which hepatitis D uses as an envelope to form new viral particles. Therefore, hepatitis D develops only in people who are already infected with hepatitis B virus or who become infected with HBV and HDV at the same time.

This feature makes hepatitis D a unique infection. On the one hand, without hepatitis B, virus D cannot maintain disease. On the other hand, when HDV joins HBV, the course of liver disease often becomes significantly more severe. The patient’s risk of rapid fibrosis progression, cirrhosis, liver failure and hepatocellular carcinoma increases. This is why detection of hepatitis D is highly important in all patients with chronic hepatitis B.

Hepatitis D is often underestimated. This is partly because patients with chronic HBV may be followed for a long time without extended testing for HDV, especially if the disease has no pronounced symptoms. However, the absence of complaints does not exclude active liver inflammation. In some cases, HDV coinfection explains faster worsening of liver markers or fibrosis progression despite relatively moderate HBV viral activity.

How infection occurs

Transmission of hepatitis D virus is linked to the same routes as transmission of hepatitis B virus. The main routes include contact with infected blood, non-sterile injection instruments, certain medical or cosmetic procedures when safety rules are violated, sexual transmission and transmission from mother to child, although the latter route is considered less common for HDV than for HBV.

From a clinical perspective, it is important to distinguish two situations:

1. Coinfection — simultaneous infection with HBV and HDV.
   In this case, the disease may present as acute viral hepatitis. In some patients, infection ends in recovery, but severe inflammation of the liver is possible in a more serious course.
2. Superinfection — infection with virus D in a person who already has chronic hepatitis B.
   This variant is considered more dangerous. The patient already has the viral basis needed for HDV persistence, so the infection more often becomes chronic and may sharply accelerate liver damage.

It is especially important that a person may not know about chronic hepatitis B until hepatitis D or complications of liver disease are detected. Therefore, HBV screening and subsequent testing for HDV in HBsAg-positive patients are important elements in preventing severe outcomes.

Why hepatitis D damages the liver faster

Hepatitis D is considered one of the most aggressive forms of chronic viral hepatitis. In this infection, liver inflammation is often more pronounced, and fibrosis may progress faster than in isolated chronic hepatitis B. The reasons are related both to the characteristics of the virus itself and to the immune response of the body.

Virus D has a small genome and uses mechanisms of the liver cell for its replication. At the same time, the immune system reacts to infected cells and maintains chronic inflammation. If inflammation persists for a long time, normal liver tissue is gradually replaced by connective tissue. This is how fibrosis forms. With further progression, cirrhosis may develop — a condition in which liver structure is disrupted, blood flow through the organ worsens and functional reserve decreases.

The danger of hepatitis D is that severe changes may develop before the patient feels pronounced symptoms. Fatigue, discomfort in the right upper abdomen, reduced appetite or weakness are nonspecific and may be absent. Therefore, it is not reliable to judge disease activity only by how the patient feels. Laboratory markers, virological tests and methods for assessing fibrosis are needed.

Diagnosis: who should be tested for HDV

The main diagnostic rule is simple: if a patient has detectable HBsAg, meaning current hepatitis B is confirmed, testing for hepatitis D should be considered. This is especially important when liver enzymes are elevated, signs of fibrosis or cirrhosis are present, liver condition worsens quickly or risk factors for infection exist.

Diagnosis usually includes several stages:

1. Detection of antibodies to HDV.
   This is the first screening step and shows whether there has been contact with virus D.
2. Detection of HDV RNA.
   This test confirms active viral replication and helps determine whether the infectious process is ongoing.
3. Assessment of HBV activity.
   Even in the presence of HDV, it is important to evaluate HBV DNA, HBsAg, HBeAg and other markers, because virus B remains a necessary condition for virus D to exist.
4. Assessment of liver condition.
   Liver tests, complete blood count, markers of liver synthetic function, ultrasound, elastography and other methods are used when indicated.

This comprehensive approach is necessary because the diagnosis of hepatitis D is not only the fact that the virus is present. It is important to understand how active the inflammation is, whether fibrosis or cirrhosis is present, whether antiviral therapy is needed, what the risk of complications is and how often the patient should be monitored.

Modern treatment: why hepatitis D has long been a difficult task

Historically, treatment of chronic hepatitis D was limited. Interferon-based therapy was used and could reduce infection activity in some patients, but tolerability was difficult and sustained response was not always achieved. Interferon is associated with significant adverse effects and is not suitable for all patients, especially in decompensated cirrhosis, severe comorbidities or high complication risk.

The main difficulty in treating HDV is connected with its dependence on HBV and with the specific features of its life cycle. Simple suppression of HBV is not always sufficient to control virus D, because HDV may maintain its own activity when HBsAg is present. Therefore, effective therapy requires approaches that affect specific stages of viral entry into the cell, viral assembly or interaction with virus B.

One important modern direction is therapy that blocks viral entry into liver cells. This approach is aimed at preventing viral particles from entering hepatocytes and thereby reducing the spread of infection within liver tissue. The emergence of specific drugs against HDV has become a significant stage because, for the first time, it has become possible to treat the disease not only through nonspecific immune stimulation, but through a more directed antiviral mechanism.

Why treatment does not replace follow-up

Even with the emergence of new drugs, hepatitis D remains a disease requiring long-term monitoring. The reason is that many patients may already have fibrosis or cirrhosis by the time of diagnosis. If structural changes in the liver have already formed, the risk of complications remains even when viral activity decreases. Therefore, treatment must be combined with regular assessment of liver function and monitoring for possible complications.

Patients with cirrhosis require especially careful management. The physician assesses signs of portal hypertension, the risk of bleeding from varicose veins, the presence of ascites, blood clotting disorders, albumin level, bilirubin level and other markers of liver function. In addition, in chronic viral liver diseases, monitoring for hepatocellular carcinoma is important. Regular imaging and laboratory evaluation are usually used according to individual indications.

It is also important to control additional factors that may accelerate liver damage. These include alcohol, obesity, diabetes mellitus, insulin resistance, fatty liver disease, other viral infections, some medication-related effects and immune disorders. If a patient has both HDV and metabolic risk factors, the burden on the liver increases, and the follow-up strategy must be especially consistent.

Prevention: why vaccination against HBV also protects against HDV

Because hepatitis D virus cannot exist without hepatitis B virus, prevention of HBV is also prevention of HDV. Vaccination against hepatitis B protects against HBV infection and therefore deprives virus D of the necessary basis for replication. This makes vaccination one of the most effective tools for preventing hepatitis D.

Prevention also includes safe medical procedures, sterile instruments, control of donated blood, reducing the risk of contact with infected blood and informing people from risk groups. For patients who already have chronic hepatitis B, it is important to be tested for HDV at least once, and when risk factors or clinical indications are present, repeat testing may be performed according to the physician’s decision.

Testing household members and sexual partners of patients with HBV also has separate importance. If close contacts do not have immunity to hepatitis B, vaccination may be recommended. This approach reduces the risk of HBV transmission and therefore prevents possible development of HDV infection.

Main conclusion

Hepatitis D is a rare but clinically significant liver infection that is impossible without hepatitis B virus. Its danger lies in the fact that it can sharply accelerate liver damage and increase the risk of cirrhosis, liver failure and liver cancer. At the same time, the disease may remain without specific symptoms for a long time, so diagnosis must rely not on how the patient feels, but on laboratory and instrumental data.

Modern hepatology is gradually gaining more precise tools for treating HDV, but the foundation of patient management remains timely detection, fibrosis assessment, liver function control, monitoring for complications and prevention of HBV transmission. The most reliable way to prevent hepatitis D is protection against hepatitis B, primarily through vaccination. Hepatitis D therefore demonstrates an important principle of liver medicine: even a rare infection may have severe consequences if it is not searched for deliberately and controlled systematically.