Herpes simplex virus

Many people have a tiny germ.

This germ is very common. It can live in the body for a long time. It hides in the nerves to stay safe.

Sometimes, the germ wakes up. It moves to the skin. It can make small, watery bumps. These bumps may turn into scabs. Most people do not even feel sick. You can catch it from skin contact. It does not live long on things like towels.

It is a very busy little germ.

Herpes simplex viruses are very common germs. There are two main types called HSV-1 and HSV-2.

Many people carry these viruses. In 2016, about 67% of people under age 50 had HSV-1.

These viruses are experts at hiding. They stay in the body by hiding in nerve cells. They hide from the immune system, which is your body's defense. Sometimes, the virus wakes up. This is called a reactivation.

The virus moves from the nerve to the skin. It can make small, watery blisters. These sores often turn into scabs.

Most people do not feel sick. The virus can also be shed without any symptoms. This means the virus can spread even if you do not see sores. You can catch it through direct skin contact. It does not live long on objects like towels.

A virus is a tiny particle. It has a shell called a capsid. This shell holds the virus's DNA. The capsid is wrapped in a layer called an envelope.

This whole particle is called a virion.

Herpes simplex viruses are very common germs that affect many people. There are two main types known as HSV-1 and HSV-2.

These viruses belong to a large family called Herpesviridae. As of 2016, about 67% of people under age 50 had HSV-1. They are highly contagious and spread through close contact. Many people carry the virus but never feel sick at all. Some people might see small, watery blisters on their skin or lips. These sores eventually heal by forming a scab.

These viruses are experts at hiding inside the human body. They are called neurotropic viruses because they live in nerve cells. The virus stays safe from the immune system by hiding in the cell bodies of neurons. Sometimes, the virus wakes up in a process called reactivation.

During an outbreak, the virus travels through the nerve's long arm, called an axon. It moves from the nerve to the skin to make copies of itself. This is when new sores or blisters might appear on the body. This cycle of hiding and waking up can happen many times.

Scientists have studied these viruses for a long time to understand them. HSV has been a model virus for many studies in molecular biology. This means researchers use it to learn how cells and genes work. For example, scientists found one of the first functional promoters in eukaryotes using HSV. A promoter is a part of DNA that helps start the process of making proteins. They also studied a protein called VP16, which is a famous transcriptional activator. These discoveries help us understand how all living things use their genetic instructions.

A single virus particle is called a virion. It has a complex structure that helps it work. Inside, there is a double-stranded DNA genome. This DNA is kept inside a protein cage called a capsid. The capsid is shaped like a 20-sided object called an icosahedron.

A lipid envelope wraps around the capsid. A layer called the tegument connects the envelope to the capsid. The virus uses at least 74 different genes to build these parts. These genes control how the virus makes copies of itself.

Understanding how the virus spreads helps us stay healthy. The virus is very unstable outside of a human body. It loses its ability to infect others quickly once it hits the air. Because of this, you likely won't catch it from a towel or a toilet seat. Instead, it spreads through direct contact with skin or mucous membranes.

Most of the time, people spread the virus through asymptomatic shedding. This means the virus is present even if there are no visible sores. Even without blisters, the virus can still move from one person to another.

Herpes simplex viruses are highly contagious agents that infect most humans. There are two primary types: HSV-1 and HSV-2. Both belong to the Herpesviridae family of viruses. As of 2016, approximately 67% of the global population under age 50 carried HSV-1. These viruses are known for their ability to persist in the body indefinitely. They can cause watery blisters on the skin or mucous membranes. These membranes include the mouth, lips, nose, genitals, and eyes.

These viruses are classified as neurotropic and neuroinvasive. This means they target and enter the nervous system to survive. HSV-1 and HSV-2 hide from the immune system inside neuron cell bodies. They specifically seek out sensory ganglia to remain dormant. After an initial infection, the virus may undergo viral reactivation. During reactivation, the virus becomes active within a nerve cell. It then travels down the neuron's axon to reach the skin. Once at the surface, the virus undergoes replication and shedding. This process can lead to the appearance of new sores.

A single virus particle is called a virion. The structure of a herpes virus is quite complex. It contains a large, double-stranded, linear DNA genome. This genome is housed inside an icosahedral protein cage called a capsid. An outer lipid bilayer, known as the envelope, wraps the capsid. A layer called the tegument connects these two parts. The genome contains at least 74 genes, though some estimates suggest up to 84. These genes are organized into long unique (UL) and short unique (US) regions. The UL region contains 56 genes, while the US region contains 12.

The process of cellular entry is a highly specific sequence. First, viral glycoproteins C (gC) and B (gB) bind to heparan sulfate on the host cell. Next, glycoprotein D (gD) binds to specific entry receptors. These receptors include HVEM, nectin-1, or 3-O sulfated heparan sulfate. Nectin receptors often provide a strong attachment by aiding cell-cell adhesion. Once gD binds to HVEM, it changes shape to interact with glycoproteins H and L. This interaction triggers a complex that allows gB to puncture the cell membrane. This creates a pore through which the viral envelope enters the host cell.

Once inside the cytoplasm, the virus begins to hijack the host cell. A viral protein called ICP27 helps disrupt the host's own protein synthesis. ICP27 binds to a cellular enzyme called SRPK1. This complex moves from the cytoplasm into the cell nucleus. The viral capsid then attaches to a nuclear entry pore. The capsid contains a portal made of 12 UL6 proteins arranged in a ring. Through this portal, the DNA is ejected into the nucleus in a single linear segment. The virus then uses host machinery, like RNA polymerase II, to replicate its DNA. This process can even change how the host's chromatin is organized.

Transmission often occurs through asymptomatic shedding. This is also called subclinical shedding. It happens when the virus is present without visible blisters or sores. In one study, HSV-2 was detected in 12% to 28% of daily samples among certain groups. Most sexual transmission of HSV-2 occurs during these asymptomatic periods. HSV-1 is frequently acquired orally during childhood. However, it can also be transmitted sexually through contact with saliva. The virus is very unstable outside the human body. It loses infectivity quickly when exposed to air. Therefore, transmission via objects like towels is considered extremely unlikely.

Because of its predictable behavior, HSV has been a vital model in molecular biology. Scientists have used it to study how genes are expressed. For example, researchers discovered one of the first functional eukaryotic promoters in the HSV thymidine kinase gene. They also extensively studied the protein VP16, which acts as a transcriptional activator. Understanding these mechanisms helps researchers study broader biological systems. It also helps us understand how viruses evade the immune system. For instance, HSV can block the transport of viral antigens through a protein called ICP-47. This helps the virus remain undetected by the body's defenses.