Question

Herpes is a virus that enters the human body and remains dormant in the nervous system until it produces an outbreak, without any particular reason. Which of the following statements correctly describes herpes? A. While it remains dormant in the nervous system, the virus is in its lysogenic cycle. B. During an outbreak, the virus is in the lytic cycle. C. Herpes integrates itself into the DNA of the cell. D. All of the above.

Short answer

D. All of the above.

Step-by-step solution

Understand Herpes Virus Life Cycle

Herpes can remain dormant in the nervous system without causing symptoms. This dormancy is part of the lysogenic cycle where the viral DNA is incorporated into the host's DNA and replicates along with it without killing the host cell.

Identify the Lytic Cycle

During an outbreak of herpes, the virus enters the lytic cycle. In this phase, the virus replicates, creates new viruses, and causes the host cell to burst, leading to symptoms.

Integration of Viral DNA

Herpes virus integrates its DNA into the host cell’s DNA, which is a characteristic of the lysogenic cycle. This integration allows the virus to replicate along with the host cell until it becomes lytic.

Evaluate All Statements

From the understanding of herpes lifecycle: statement A is correct (lysogenic cycle during dormancy), statement B is correct (lytic cycle during outbreaks), and statement C is correct (integration into the DNA). Thus, statement D ('All of the above') is the correct description as it encompasses all the accurate details from the previous statements.

Key concepts

Lysogenic Cycle

The lysogenic cycle is a phase in which the herpes virus can remain inactive within a host cell. During this cycle, the viral DNA integrates into the host cell's DNA without causing damage to the cell. This means that the cell continues to function normally and replicates as usual, but it also replicates the viral DNA.
This integrated viral DNA is called a prophage when discussing bacteriophages, but in the case of the herpes virus, it’s often referred to as a latent or dormant virus. The immune system does not detect the viral DNA because it is hidden within the host's genes.
Lysogenic cycle can last for years, during which the virus does not produce any symptoms. However, it can change phases due to various factors such as stress, illness, or other triggers. Once triggered, the virus can switch to the lytic cycle, causing active infection and symptoms.

Lytic Cycle

The lytic cycle is the phase where the herpes virus becomes active and starts producing new viral particles. During this cycle, the viral DNA instructs the host cell to manufacture and assemble new viruses.
Here's how the lytic cycle progresses:

• The viral DNA takes over the host cell's machinery to replicate its genome.
• The host cell starts producing viral proteins and assembling new viruses.
• Eventually, the host cell cannot contain the new viruses, leading to the cell bursting (lysis) and the release of new viral particles.

This process leads to the symptoms of a herpes outbreak, such as sores and blisters. The immune system then responds to the outbreak, but some of the virus may re-enter the lysogenic cycle in other cells, remaining dormant until the next trigger.

Viral DNA Integration

Viral DNA integration is a crucial step in the herpes virus life cycle, specifically during the lysogenic cycle. The herpes virus has a specialized protein that enables it to integrate its DNA into the host cell's genome.
Here are the main points about viral DNA integration:

• The integration happens when the viral DNA is inserted into the host cell’s DNA.
• This integrated DNA replicates along with the host cell’s DNA during cell division.
• The viral genes remain inactive while integrated, which prevents them from producing viral particles.

This integration allows the herpes virus to persist in the host long-term. Because the viral DNA is part of the host's genetic material, it is shielded from the host's immune responses. This aspect of viral life cycle is what makes herpes infections challenging to completely eradicate.

Nervous System Dormancy

Herpes virus is known for its ability to remain dormant in the nervous system. After the initial infection, the virus travels via sensory nerve cells to nerve ganglia, where it can stay inactive.
Here’s what happens during nervous system dormancy:

• The viral DNA is integrated into the nerve cells' DNA in a dormant state.
• The virus does not produce new viral particles while dormant.
• Dormancy in the nervous system allows the virus to evade the immune system.

This dormancy usually happens in the trigeminal ganglion or sacral ganglion, depending on the type of herpes infection.
Various triggers such as stress, hormonal changes, and illness can activate the virus, leading it to travel back to the skin or mucous membranes and cause an outbreak. This persistent ability to switch between dormancy and activity makes herpes a lifelong condition for those infected.