Hepatitis D is a serious viral liver infection that can only occur in people who already have hepatitis B. This unique relationship between two viruses makes hepatitis D both preventable through hepatitis B vaccination and particularly severe when it develops, often leading to more rapid liver damage than hepatitis B alone.

Understanding Hepatitis D and How Common It Is

Hepatitis D is caused by the hepatitis D virus, also known as HDV or the delta virus. This virus is unusual because it cannot survive or reproduce on its own. It needs the hepatitis B virus to function, acting like a parasite that depends completely on hepatitis B for its existence. Scientists sometimes call HDV a “satellite virus” because of this dependency. When HDV enters the body, it wraps itself in the surface proteins of the hepatitis B virus, using them as a disguise to enter liver cells. Without hepatitis B, hepatitis D simply cannot infect anyone.^[1]

The exact number of people affected by hepatitis D worldwide is difficult to determine because tracking varies by country. However, research suggests that approximately 5% of people who have chronic hepatitis B are also infected with hepatitis D, which translates to about 12 million people globally. This makes hepatitis D relatively uncommon compared to other forms of viral hepatitis, though it remains a significant health concern in certain regions.^[3]

Hepatitis D is considered uncommon in the United States, and because it is not a nationally notifiable condition in the country, the actual number of cases remains unknown. The disease does not appear in routine disease surveillance reports the way some other infectious diseases do, which can make it easy for healthcare systems to overlook.^[1]

Geographically, hepatitis D is not distributed evenly around the world. Certain regions have much higher rates of infection. The disease is most common in Eastern Europe, Southern Europe, the Mediterranean region, the Middle East, West and Central Africa, East Asia, and the Amazon Basin in South America. Specific hotspots with particularly high rates include Mongolia, the Republic of Moldova, and several countries in western and central Africa. In these areas, hepatitis D affects a larger proportion of people with hepatitis B, making it a more pressing public health issue.^[1][3]

Certain populations are more likely to have both hepatitis B and hepatitis D infections. These include indigenous populations in endemic areas, people who receive hemodialysis treatments for kidney disease, and people who inject drugs. The overlap between these groups and hepatitis D prevalence reflects both the transmission routes of the virus and the vulnerabilities of specific communities.^[3]

What Causes Hepatitis D

Hepatitis D is caused by infection with the hepatitis D virus. This virus has a unique structure: it consists of a small piece of genetic material (RNA) surrounded by a protein shell, all wrapped in an envelope made from hepatitis B surface proteins. The genetic material of HDV is remarkably small compared to other viruses, making it one of the smallest known agents that can cause disease in humans. Some scientists believe HDV may have evolved from plant viroids, which are even simpler infectious particles that affect plants.^[7]

Once inside the body, HDV relies entirely on hepatitis B for its survival and spread. The virus enters liver cells through specific receptors that normally help the liver process bile acids. After entering the liver cell, HDV takes over some of the cell’s machinery to make copies of itself. Interestingly, even though HDV needs hepatitis B to enter and exit cells, once inside a liver cell, HDV can reproduce independently of hepatitis B. This creates a complex infection where two different viruses coexist in the same organ.^[4]

An unusual feature of hepatitis D infection is that it actually suppresses the replication of hepatitis B virus. When both viruses are present in the liver, HDV tends to dominate, and hepatitis B virus levels often decrease. Scientists do not fully understand why this happens, but it means that people with both infections may have lower levels of hepatitis B virus in their blood than those with hepatitis B alone. However, this suppression does not make the infection less dangerous; in fact, the combination often causes more severe liver disease.^[4]

Liver damage from hepatitis D occurs through two main mechanisms. First, the virus itself can directly damage liver cells as it reproduces. Second, the body’s immune system responds to the infection by attacking infected liver cells, trying to eliminate the virus. This immune response, while intended to be protective, contributes to inflammation and injury in the liver. Over time, repeated cycles of damage and attempted healing lead to scarring of the liver tissue, a condition called cirrhosis.^[4]

How Hepatitis D Spreads from Person to Person

Hepatitis D spreads through contact with infected blood or other body fluids. The virus is present in the bloodstream and certain body fluids of infected individuals, and transmission occurs when these fluids enter another person’s body. This is similar to how hepatitis B spreads, which makes sense given that both viruses must be present for hepatitis D infection to occur.^[1]

One of the most common ways hepatitis D spreads is through sharing needles or other equipment used to inject drugs. When needles, syringes, or other drug preparation equipment are shared among people who inject drugs, small amounts of blood from one person can be transferred to another. If the first person has hepatitis D (and therefore also has hepatitis B), the virus can be transmitted this way. This is why people who inject drugs are at particularly high risk for hepatitis D infection.^[1]

Sexual transmission is another route by which hepatitis D can spread. The virus can be transmitted during vaginal, oral, or anal sex with an infected partner. Sexual contact can involve exposure to body fluids that contain the virus, allowing transmission between partners. People with multiple sexual partners or those who do not use barrier protection during sex face increased risk.^[2]

Healthcare settings can occasionally be sources of transmission, though this is rare in countries with strong infection control practices. Accidental needle sticks, where a healthcare worker is punctured by a needle that has been used on an infected patient, can transmit the virus. Similarly, exposure to blood or blood-contaminated body fluids in medical settings poses a risk. Healthcare and public safety workers who regularly come into contact with blood must follow strict safety protocols to prevent exposure.^[1]

Transmission from mother to baby during childbirth is possible but rare. A mother infected with hepatitis D can potentially pass the virus to her baby during delivery, when the baby comes into contact with the mother’s blood and body fluids. However, this vertical transmission occurs much less frequently with hepatitis D than with some other bloodborne viruses.^[1]

Household contacts of people with hepatitis D may also be at risk if they share personal items that could have trace amounts of blood on them. Items like razors, toothbrushes, nail clippers, or any personal care items that might come into contact with blood can potentially transmit the virus between household members. Contact with open sores or wounds of an infected person can also lead to transmission.^[1]

People receiving hemodialysis for kidney disease face elevated risk because of the potential for blood exposure during treatment. Hemodialysis involves filtering blood through a machine, and despite careful cleaning protocols, there remains a small risk of blood-to-blood contact in dialysis centers, particularly if multiple patients are treated in the same facility.^[1]

Who Is Most at Risk for Hepatitis D

The single most important risk factor for hepatitis D is having a hepatitis B infection. Since hepatitis D cannot occur without hepatitis B, anyone with chronic hepatitis B is potentially at risk for developing hepatitis D if they are exposed to HDV. This means that protecting yourself from hepatitis B through vaccination automatically protects you from ever getting hepatitis D.^[1]

People who inject drugs face significantly elevated risk for hepatitis D. The act of injecting drugs, particularly when needles or other equipment are shared, creates opportunities for blood-to-blood contact. Even small amounts of blood remaining on shared needles or in shared drug preparation equipment can transmit the virus. The more frequently someone injects drugs and the more often equipment is shared, the higher the risk becomes.^[1]

Having sexual partners who are infected with both hepatitis B and hepatitis D increases risk. The virus can spread through sexual contact, so people whose partners have these infections should take precautions to protect themselves. This includes using barrier methods during sex and considering vaccination against hepatitis B if not already immune.^[1]

Men who have sex with men are identified as a higher-risk group for hepatitis D. This increased risk relates to transmission patterns and network effects within this community, particularly in areas where hepatitis B prevalence may already be higher. The risk can be mitigated through hepatitis B vaccination and safer sex practices.^[1]

People who also have HIV infection along with hepatitis B face increased risk for hepatitis D. The combination of multiple viral infections can complicate the clinical picture and make management more challenging. HIV affects the immune system, which may influence how hepatitis D progresses if infection occurs.^[1]

Household contacts of someone with hepatitis D have elevated risk compared to the general population. Living in close quarters with an infected person increases chances of exposure through shared personal items or accidental contact with blood. Family members should be aware of how the virus spreads and take precautions like not sharing razors or toothbrushes.^[1]

Healthcare and public safety workers who may be exposed to blood or blood-contaminated body fluids during their work are at occupational risk. This includes doctors, nurses, laboratory technicians, emergency responders, and others whose jobs involve potential contact with patients’ blood or body fluids. Strict adherence to standard precautions and infection control measures helps minimize this risk.^[1]

Symptoms and How Hepatitis D Affects the Body

Symptoms of hepatitis D typically appear between 3 and 7 weeks after infection with the virus. The symptoms can vary in severity depending on whether someone has a coinfection (getting both hepatitis B and D at the same time) or a superinfection (getting hepatitis D when already infected with hepatitis B). Generally, people with hepatitis D experience more severe symptoms than those who have hepatitis B alone.^[1]

One of the most distinctive symptoms is jaundice, which is a yellowing of the skin and the whites of the eyes. Jaundice occurs when the damaged liver cannot properly process a substance called bilirubin, which builds up in the body. Before jaundice becomes visible, people often notice that their urine has become very dark, like tea or cola, and their stools have become pale or clay-colored. These changes in urine and stool color are related to the same problem with bilirubin processing.^[1]

Fatigue is another common symptom. People with hepatitis D often feel extremely tired and weak, with a profound lack of energy that interferes with daily activities. This exhaustion is not relieved by rest and can be one of the most debilitating aspects of the infection. The tiredness stems from the body’s efforts to fight the infection and the liver’s reduced ability to perform its normal functions.^[1]

Digestive symptoms are frequent and troublesome. These include nausea, stomach pain, and vomiting. People may completely lose their appetite, not feeling hungry even when they have not eaten for many hours. This loss of appetite combined with nausea can lead to weight loss and nutritional deficiencies if the infection persists.^[1]

Fever and joint pain can occur, particularly in the early stages of infection. The fever is usually mild to moderate and represents the body’s immune response to the viral infection. Joint pain can affect multiple joints throughout the body and adds to the overall feeling of illness and discomfort.^[1]

In people who already have chronic hepatitis B and then develop hepatitis D as a superinfection, symptoms may return suddenly or existing symptoms may worsen dramatically. A person who had stable, perhaps even asymptomatic hepatitis B might suddenly develop severe liver inflammation symptoms. This pattern—sudden worsening in someone with known hepatitis B—should prompt testing for hepatitis D.^[1]

People with coinfection (both viruses at once) may experience two separate periods of symptoms. This happens because hepatitis B symptoms can appear at a different time than hepatitis D symptoms. Healthcare providers might observe two distinct peaks in liver enzyme levels as each virus takes its turn affecting the liver most strongly.^[1]

Not everyone with hepatitis D will experience obvious symptoms, especially early in the infection. Some people have what is called asymptomatic infection, where the virus is present and causing liver damage but without producing noticeable symptoms. These individuals may only discover they have hepatitis D through blood tests done for other reasons.^[2]

Ways to Prevent Hepatitis D Infection

The most effective way to prevent hepatitis D is to prevent hepatitis B infection. Because hepatitis D cannot exist without hepatitis B, anyone who is protected from hepatitis B is automatically protected from hepatitis D as well. This makes hepatitis B vaccination the primary prevention tool for hepatitis D.^[1]

The hepatitis B vaccine is safe, effective, and widely available. It is typically given as a series of three or four shots over several months. The vaccine stimulates the immune system to produce antibodies against hepatitis B virus, which then protect against both hepatitis B and, indirectly, hepatitis D. Many countries now include hepatitis B vaccination in routine childhood immunization schedules, which has dramatically reduced hepatitis B rates and will likely reduce hepatitis D rates over time.^[1]

For people who already have chronic hepatitis B, preventing hepatitis D requires avoiding exposure to the virus. This means never sharing needles or other equipment used to inject drugs. Even needles used for legitimate medical purposes, like insulin injection for diabetes, should never be shared. Each person should use their own sterile equipment and dispose of it safely after use.^[1]

Using condoms consistently and correctly during sexual activity can reduce the risk of transmission. Latex or polyurethane condoms provide a barrier that prevents contact with body fluids that might contain the virus. People with hepatitis B who want to protect their sexual partners from potential hepatitis D exposure should use condoms during all types of sexual activity.^[3]

Not sharing personal care items that might have trace amounts of blood on them is another important prevention measure. Razors, toothbrushes, nail clippers, and similar items should be kept strictly personal. Even tiny amounts of blood invisible to the naked eye can potentially transmit bloodborne viruses.^[1]

Healthcare workers can protect themselves by following standard precautions and infection control procedures. This includes wearing appropriate protective equipment like gloves when handling blood or body fluids, disposing of needles in puncture-resistant sharps containers, and never recapping used needles. Healthcare facilities should have clear protocols for preventing occupational exposure to bloodborne pathogens.^[1]

Pregnant women with hepatitis B should receive prenatal care that includes assessment for hepatitis D. While transmission from mother to baby is rare, healthcare providers can take extra precautions during delivery if they know the mother is infected. Babies born to mothers with hepatitis B should receive hepatitis B vaccination starting at birth, which will protect them from both hepatitis B and hepatitis D.^[1]

Changes in the Body: Understanding the Disease Process

When hepatitis D virus enters the body, it must first travel through the bloodstream to reach the liver. The virus can only enter liver cells (called hepatocytes) by attaching to specific receptors on the cell surface. These receptors normally help the liver cells absorb bile acids, which are important for digestion. The hepatitis D virus, wrapped in its coat of hepatitis B surface proteins, tricks these receptors into letting it enter the cell.^[11]

Once inside a liver cell, the hepatitis D virus releases its genetic material into the cell’s nucleus, which is like the cell’s control center. The virus then hijacks the cell’s normal machinery for reading and copying genetic information. Unlike many viruses that bring their own tools for copying themselves, hepatitis D uses the liver cell’s RNA polymerase—an enzyme the cell normally uses for its own purposes. This is one reason why hepatitis D is so difficult to treat: it does not have its own unique enzymes that drugs could target.^[11]

As the virus makes copies of itself inside liver cells, it causes damage through multiple mechanisms. The virus can directly harm the cells as it reproduces and eventually bursts out to infect more cells. This direct cell damage is called a cytopathic effect. Additionally, the immune system detects that liver cells are infected and sends immune cells to attack them. While this immune response is trying to eliminate the virus, it also kills infected liver cells, contributing to inflammation and damage.^[11]

The body tries to repair this ongoing damage, but with chronic hepatitis D, the damage happens faster than complete healing can occur. As liver cells die, they are replaced by scar tissue in a process called fibrosis. Over time, this fibrosis can progress to cirrhosis, where large portions of the normal liver tissue have been replaced by scar tissue. A cirrhotic liver has a bumpy, nodular surface instead of being smooth, and it cannot perform its normal functions effectively.^[1]

The liver performs hundreds of essential functions in the body. It filters toxins from the blood, produces proteins needed for blood clotting, stores vitamins and minerals, processes nutrients from food, and produces bile for digestion. When hepatitis D causes progressive liver damage, all of these functions can be impaired. This leads to complications like fluid accumulation in the abdomen (ascites), confusion from toxins building up in the brain (hepatic encephalopathy), easy bleeding, and yellowing of the skin.^[2]

One of the unusual features of hepatitis D is its effect on hepatitis B replication. When both viruses are present in liver cells, hepatitis D suppresses the reproduction of hepatitis B virus. Scientists have observed that people infected with both viruses often have lower levels of hepatitis B virus in their blood than people with hepatitis B alone. The exact mechanism is not fully understood, but it may involve competition for resources within the liver cell or direct interference by hepatitis D with hepatitis B’s replication process.^[4]

Chronic infection with both hepatitis B and hepatitis D is considered the most severe form of chronic viral hepatitis. The combination causes more rapid progression to cirrhosis than hepatitis B alone. Studies have shown that people with both infections develop severe liver disease, liver failure, and hepatocellular carcinoma (liver cancer) more frequently and more quickly than those with hepatitis B only. In fact, hepatitis D has been classified as carcinogenic to humans—meaning it can cause cancer—just like hepatitis B and hepatitis C.^[3]

The rate of progression to severe disease depends partly on whether someone has a coinfection or superinfection. Coinfection, where both viruses are acquired at the same time, can cause severe acute illness but does not always lead to chronic infection. Less than 5% of adults with coinfection develop both chronic hepatitis B and chronic hepatitis D. However, superinfection—when hepatitis D is acquired by someone who already has chronic hepatitis B—is much more likely to result in chronic hepatitis D infection. People with superinfection often experience rapid development of liver fibrosis and face a higher risk of liver failure and death.^[3]

In the most severe cases, hepatitis D can cause fulminant hepatitis, which is sudden and severe liver failure. Between one quarter and one half of fulminant hepatitis B cases are actually due to concurrent infection with hepatitis D. In fulminant hepatitis, the liver damage occurs so rapidly that the liver cannot perform its vital functions, leading to a medical emergency. People with fulminant hepatitis need intensive medical care and may require urgent liver transplantation to survive.^[6]