Infectious Diseases and Clinical Microbiology

Infectious Diseases: Diagnosis, Treatment & Travel Medicine

Infectious diseases specialists diagnose and treat infections from bacteria, viruses, fungi, and parasites, focusing on fevers, antibiotics, and vaccines.

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The Pathophysiology and Virology of Hepatitis B Infection

Hepatitis B

Hepatitis B is a complex viral infection that attacks liver cells and can cause anything from short-term inflammation to lifelong liver disease. At Liv Hospital’s Department of Infectious Diseases and Clinical Microbiology, Hepatitis B is seen as more than just a local infection—it involves the whole immune system interacting with the Hepatitis B Virus (HBV). HBV, part of the Hepadnaviridae family, has a unique way of replicating. It uses reverse transcription, which lets it stay in the nucleus of liver cells as covalently closed circular DNA (cccDNA). This ability to persist is what makes Hepatitis B a long-term condition that often needs ongoing care.

Hepatitis B infection is defined by the ongoing battle between the virus and the body’s immune system. The liver, which handles detoxification, protein production, and digestion, is at the center of this process. When HBV infects liver cells, it does not kill them directly. Instead, the immune system, especially cytotoxic T cells, attacks the infected cells, causing liver cell death and inflammation—this is what we call hepatitis. How severe this inflammation is determines the symptoms, and if the immune system cannot fully clear the virus, the infection becomes chronic.

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Classification of Hepatitis B Clinical States

Hepatitis B

Doctors classify Hepatitis B based on how long the infection lasts and the patient’s blood test results. Knowing these categories helps decide the outlook for the patient and whether treatment is needed.

  • Acute Hepatitis B
    This stage is the first sign of illness after someone is exposed to the virus. Most adults can fight off the virus, so the illness usually goes away on its own and leads to lifelong immunity. However, during the early phase, people can have high levels of the virus and spread it to others even before they feel sick.
  • Chronic Hepatitis B
    Chronic Hepatitis B is diagnosed when the surface antigen (HBsAg) stays in the blood for six months or more, showing that the immune system has not cleared the virus. This long-term infection can go through different phases, from the immune system ignoring the virus to trying to fight it. Chronic infection is the main cause of serious problems like cirrhosis and liver cancer.

Occult Hepatitis B Infection
Occult Hepatitis B is a less recognized form where the virus’s DNA can be found in the liver (and sometimes in the blood at very low levels), even though the usual surface antigen (HBsAg) is not detected. This hidden infection can become active again, especially if the immune system is weakened.

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The Anatomy of the Hepadnavirus

Hepatitis B

Hepatitis B is a DNA virus with an outer envelope that makes it tough and able to cause disease. The surface antigen on this envelope is what doctors look for in tests and what is used in vaccines. Inside, the core contains the virus’s DNA and the enzyme it needs to copy itself.

When the virus enters a liver cell, it moves its DNA into the cell’s nucleus, where it forms cccDNA. This cccDNA acts as a stable template for making new virus particles. Because cccDNA can stay hidden in the nucleus for the life of the cell, it is very hard to remove the virus completely. That’s why doctors talk about a “functional cure” (controlling the virus) instead of a “sterilizing cure” (removing it entirely) for chronic Hepatitis B.

Epidemiology and the Global Infectious Burden

Hepatitis B is a major global health problem, with rates that differ widely by region. The virus is very contagious—much more than HIV—and can survive outside the body for at least a week, making it easy to spread. In places where the virus is common, most people get infected as babies or young children, which often leads to chronic infection. In areas where it is less common, adults usually catch it from each other, and these infections are more likely to clear up on their own.

The impact of Hepatitis B goes beyond the initial infection. Ongoing liver inflammation can cause scarring (fibrosis) as the liver tries to heal itself. Over many years, this scarring can become cirrhosis, which permanently damages the liver and affects blood flow. The virus’s DNA can also join with the host’s DNA, raising the risk of liver cancer even if cirrhosis has not developed.

Hepatitis B

The Immunological Interface

How the body’s immune system responds to Hepatitis B is key to what happens after exposure. At Liv Hospital, doctors note that a strong and targeted T-cell response usually clears the virus and causes only short-term illness. If the T-cell response is weak or becomes worn out, the virus stays in the body and the infection becomes chronic. This happens because certain signals on T-cells stop them from killing infected liver cells. Learning more about this process is important for creating new treatments that help the immune system fight the virus.

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FREQUENTLY ASKED QUESTIONS

What is the difference between being a carrier and having chronic Hepatitis B?

Being a “carrier” is an older term often used to describe the “inactive carrier state” of chronic Hepatitis B. It implies that a person has the virus in their body (Chronic Hepatitis B) but currently has normal liver enzyme levels and low viral activity, resulting in minimal liver damage at that time. However, the virus is still present, and the condition can reactivate. Therefore, medical professionals prefer the terms “Chronic Infection” or “Inactive Chronic Hepatitis B” to emphasize the need for ongoing monitoring.

No, Hepatitis B cannot turn into Hepatitis C. They are caused by two distinct viruses with different genetic structures and replication modes. However, an individual can be co-infected with both viruses simultaneously. Co-infection creates a more complex clinical picture and can accelerate the progression of liver disease, requiring specialized management strategies.

The Hepatitis B virus is found in the highest concentrations in blood, serum, and wound exudates. It is also present in moderate concentrations in semen, vaginal fluid, and saliva. While it can be detected in very low levels in tears, sweat, urine, and breast milk, these fluids are not considered efficient vehicles for transmission unless they are visibly contaminated with blood.

A functional cure is defined as the sustained loss of Hepatitis B surface antigen (HBsAg) from the blood, with or without the development of antibodies, after a finite course of treatment. While the virus’s genetic template (cccDNA) may remain dormant in the liver cells, the immune system effectively controls the virus without medication, and the risk of liver complications is significantly reduced. This is the current goal of advanced therapies.

Hepatitis B is often termed a “silent infection” because many people, especially those who acquire the virus at birth or in early childhood, do not experience any noticeable symptoms for decades. During this asymptomatic phase, the virus can continue to replicate and cause low-level liver damage. Often, the diagnosis is only made when advanced liver disease, such as cirrhosis or liver failure, has already developed.

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