Hepatitis B virus

The Hepatitis B virus (HBV) is a virus that can make people very sick. It is a special kind of virus called a partially double-stranded DNA virus. This means it has DNA, which helps it copy itself inside our bodies.

HBV belongs to a group of viruses known as the genus Orthohepadnavirus and is part of the Hepadnaviridae family. This family includes viruses that can affect the liver in animals and humans.

When this virus infects a person, it causes a disease called hepatitis B. This disease can cause serious health problems, especially if it is not treated. Learning about HBV helps doctors and scientists find ways to prevent and cure it.

Classification

Hepatitis B virus belongs to a group called Orthohepadnavirus. This group is part of a larger family of viruses known as Hepadnaviridae. This family also includes other groups like Avihepadnavirus.

The virus has been found in many types of primates, including apes and monkeys. This suggests the virus has been around in primates for a very long time. Scientists study the virus's features and genetic makeup to understand how it spreads and makes people sick.

Morphology

The Hepatitis B virus is part of the Hepadnavirus family. The virus looks like a small ball with a lipid outer layer and a protein core inside. This core holds the virus’s DNA and a special enzyme.

The outer layer has proteins that help the virus attach to and enter cells. The virus is very small, measuring 42 nanometers in diameter.

Evolution

The early history of the Hepatitis B virus (HBV) is hard to trace, like other viruses. We know that similar viruses have been in animals for a very long time. Evidence shows these viruses have been in birds for at least 70 million years. They may have also been in the ancestors of birds and mammals over 300 million years ago.

Recently, scientists have studied very old human remains to learn about HBV’s history in people. In 2021, a study found that HBV has been in humans for at least 10,000 years. The virus was already present between 20,000 and 12,000 years ago. The virus’s changes match big events in human history, like when people first moved to the Americas. Some ancient types of HBV still exist today, while others are gone. HBV types found in some apes, like chimpanzees and gorillas, seem connected to human HBV, suggesting the virus may have moved between species in the past.

Genome

The genome of the Hepatitis B virus (HBV) is made of circular DNA. This DNA is special because it is not fully double-stranded. One end of the long strand is linked to a viral enzyme. The genome is about 3020 to 3320 small building blocks called nucleotides long for the long strand and 1700 to 2800 nucleotides long for the short strand.

The virus has four main genes: C, P, S, and X. Gene C makes a protein called the core protein. Gene P makes an enzyme needed for the virus. Gene S makes a protein that appears on the surface of the virus. The job of the protein from gene X is not completely known, but it might help the virus use the cell's tools. There are also different versions of the virus, called genotypes, found in different parts of the world. These genotypes are labeled A through J, each with its own subtypes.

Life cycle

The life cycle of hepatitis B virus is complex. This virus is special because it uses a process called reverse transcription to make copies of itself, even though it is not a retrovirus.

The virus enters cells by attaching to special parts on the cell's surface and moving inside through a process called endocytosis. Once inside, the virus releases its genetic material into the cell's center. This material then moves to the cell's nucleus, where it is changed and used to make new copies of the virus. These new copies are then assembled and released from the cell to start the cycle again.

Disease

Main article: Hepatitis B

Even though there is a vaccine to prevent hepatitis B, it is still a problem in many parts of the world. Hepatitis B can start with mild symptoms but may become a longer-lasting condition. This can lead to serious problems in the liver and, in some cases, a type of liver cancer.

The hepatitis B virus changes liver cells by using its own proteins and by increasing harmful substances inside the cells. Over time, these changes can cause inflammation and damage to the liver. The virus has been known for a very long time, with early records mentioning symptoms like yellowing of the skin. Today, vaccines help protect people from getting infected, and these vaccines have been used since the 1980s to keep many people safe.