Hepatitis B

Hepatitis B is an infectious disease caused by the hepatitis B virus that affects the liver. It can cause both short-term and long-term infections. Many people may not feel sick after being exposed, but for others, symptoms can appear weeks to months later and may include feeling very sick, having a yellow color on the skin or in the urine, and feeling very tired.

The virus is spread by contact with infected blood or body fluids. In places where the disease is common, it is often passed from a mother to her baby at birth or through contact with blood during childhood. In areas where it is less common, it can spread through certain activities or medical treatments. The disease can be diagnosed by testing blood for parts of the virus.

Since 1982, a vaccine has been available to prevent hepatitis B, and it is very effective. The World Health Organization recommends that all babies receive the vaccine soon after birth. This helps protect them and prevent the disease from spreading. Even today, many people around the world live with hepatitis B, and efforts continue to control and eliminate it through vaccines and safe practices.

Signs and symptoms

When someone gets infected with the hepatitis B virus for a short time, they might feel generally unwell. They could lose their appetite, feel sick, vomit, have body aches, and have a mild fever. Their urine might look dark, and their skin or the whites of their eyes might turn yellow, a condition called jaundice. Most people get better after a few weeks.

Sometimes, the infection can become long-lasting and may not cause any symptoms at first. Over many years, this can lead to problems in the liver, such as scarring. It can also increase the chance of developing liver cancer. People with this long-lasting infection are advised to avoid alcohol, as it can make liver problems worse. The virus has also been linked to certain kidney problems.

Cause

Transmission

Hepatitis B spreads when a person comes into contact with infectious blood or body fluids that contain blood. The virus is much more contagious than HIV. It can be passed from a mother to her baby during childbirth. Without proper medical help, there is a risk of passing the infection this way. It can also spread through bites, certain personal habits, or contact with secretions. In adults, it can be passed through contact with infected blood, such as through reused needles or medical equipment.

Virology

Structure

Hepatitis B is part of a special group of viruses. It has a outer layer and a core that contains important parts of the virus, including its genetic material and enzymes needed for copying itself.

Genome

The genetic material of Hepatitis B is made of circular DNA, which is partly double-stranded. It has genes that code for important proteins, some of which help the virus infect cells and others that may play a role in causing liver disease.

Pathogenesis

Hepatitis B enters liver cells and uses the cell's machinery to make copies of itself. It can create a lasting piece of DNA in the cell's nucleus, which helps it continue to produce more virus particles.

Serotypes and genotypes

The virus has different types, called genotypes, which are found in different parts of the world. These types can affect how severe the disease is and how it responds to treatment.

Mechanisms

The hepatitis B virus affects the liver by growing inside special cells called hepatocytes. It uses a part called NTCP to get into these cells. The body’s immune system tries to fight the virus, which can cause some damage to the liver. Special cells called cytotoxic T lymphocytes help remove the virus by targeting the infected cells. This process can sometimes cause inflammation in the liver, but it helps clear the virus from the body.

Diagnosis

To find out if someone has hepatitis B, doctors use special tests called assays. These tests look at serum or blood tests to see if there are parts of the virus or the body’s defense against it called antibodies.

One important test looks for something called the hepatitis B surface antigen (HBsAg). This is often the first sign that someone has the infection. Sometimes, it might not show up right away or might disappear later as the body fights the virus.

There are also other tests that can find different parts of the virus or the body’s response to it. These help doctors understand how serious the infection is and how to treat it.

Doctors also use PCR tests to measure how much of the virus is in the blood. This helps them decide on the best treatment for the person.

Prevention

Vaccine

Vaccines to help prevent hepatitis B have been given to babies in the United States since 1991. The first dose is usually given very soon after birth. This vaccine was the first to help stop a type of cancer that affects the liver.

Most vaccines are given in three doses over a few days. The vaccine works best in children, and about 95 percent of children who get the vaccine have enough protection. The vaccine’s protection lasts a long time, even if the protection level goes down.

Everyone who might come in contact with blood or other body fluids should get the vaccine if they haven’t already. It’s very important for certain groups, like healthcare workers and people with certain health conditions.

Other

People at higher risk of getting hepatitis B should get tested. This includes those who haven’t been vaccinated and come from places where hepatitis B is common, or who have certain health conditions. Testing during pregnancy is recommended in the United States.

Treatment

Most people with a new infection of hepatitis B do not need treatment, as their bodies can fight it off on their own. However, a very small number of people may need medicine right away if their infection gets very strong or if their body has trouble fighting off infections.

For people who carry the virus for a long time, treatment can help lower the chance of serious problems like liver damage or cancer. Doctors look at certain tests to decide who should get treatment, and the medicine can last from six months to a year, or sometimes longer.

While medicines can’t remove the virus, they can stop it from growing and causing more harm to the liver. There are several medicines available, and doctors choose the best one for each person based on what they need and how their body reacts. Scientists are always working to find even better ways to treat hepatitis B.

Prognosis

Hepatitis B can either go away on its own or last a long time. Most adults and older children will get better and become protected from the virus. But younger children and newborns are less likely to get better.

When someone has hepatitis B together with hepatitis D, their risk of serious liver problems goes up. Some health conditions happen more often in people with hepatitis B.

There are ways to check how much damage the liver has. Some tests can show this, but they can be costly.

Even after someone seems better, the virus can stay hidden in the body. Sometimes it can become active again, especially if the person’s health is weak or if they take certain medicines. This can be serious, and there are ways to treat it to help prevent problems.

Epidemiology

About 254 million people had a lasting infection with the hepatitis B virus in 2022. Another 1.2 million new cases happened that same year. The number of people with this infection varies a lot around the world. It is most common in parts of Africa, where up to one in fifteen people carry the virus. In places like Mongolia and parts of Europe, the numbers are much smaller.

In areas where many people have the virus, it is often passed from a mother to her baby during birth. In places where fewer people have it, the virus is usually spread between children or through other close contact. Countries such as China and India fall into this middle group. In many Western European countries and the Americas, very few people have the virus. Efforts like better medical care and vaccines have helped lower the numbers in some places.

History

Scientists have found signs of the hepatitis B virus in very old human remains, showing that people have been infected for at least 10,000 years. This helps us learn about how humans moved and lived long ago.

The first known outbreak caused by hepatitis B was described in 1885. Workers who were given a treatment using a special liquid from others got very sick. Later, many soldiers got infected during World War II after receiving a vaccine that was not clean.

The virus was finally discovered in 1966 by a scientist studying blood from people in Australia. This important find led to better ways to test and protect people from the virus.

Society and culture

World Hepatitis Day, observed on July 28, helps people learn about hepatitis B and hepatitis C. This special day encourages everyone to work together to prevent, find, and treat these illnesses. The World Hepatitis Alliance started it in 2007, and in May 2010, it received support from the World Health Organization.