Recording-2025-03-16T20:30:07.628Z Lecture 13.4

Virus Lifecycle Variations

• Some viruses deviate from the standard viral cycle, incorporating unique steps along with the general ones.

• Example: HIV exhibits extra stages in its lifecycle.

Latent Viruses

• Definition: Latent viruses enter a dormant state post-infection, remaining inside cells without actively reproducing.

• Comparison to Lysogenic Phage: Similar to lysogenic phase in bacteriophages, where it integrates into bacterial genome; however, human latent viruses don’t reproduce in the same manner.

• Reactivation Triggers: Viral reactivation is often triggered by immune system compromise, leading to its emergence when the host's immune defenses are lowered.

Herpes Viruses

• There are eight known human herpes viruses, notably types 1 and 2, which affect oral and genital areas respectively.

• Herpes Virus Type 1: Commonly causes cold sores around the mouth.

• Herpes Virus Type 2: Primarily results in genital herpes but can occur in both areas.

• Herpes Virus Type 3 (VZV): Causes chickenpox and later re-emerged as shingles.

Reactivation and Latency

• After initial infection, herpes viruses can remain inactive in nerve cells, specifically in the dorsal root ganglia.

• Reactivation occurs due to stress or immune suppression, leading to the emergence of symptoms at a later time.

• Common symptomatology includes recurrent outbreaks, especially for herpes simplex viruses (types 1 and 2).

Chickenpox and Shingles

• Initial Infection: Chickenpox (varicella) causes widespread itchy rash and is initially systemic.

• Latency: Post-infection, the virus remains dormant in the sensory nerve cells of the dorsal root ganglia.

• Reactivation as Shingles: When reactivated, symptoms manifest as shingles (zoster) characterized by localized painful rash typically along a dermatome from the spinal nerve.

• Epidemiology: Shingles often occurs during periods of immune system distress such as stress or illness.

• Pain Manifestation: Unlike the initial itchy rash from chickenpox, shingles results in acute pain localized to the affected dermatome as the virus travels down sensory nerves.

Terminology and Implications

• Chickenpox: Initial disease caused by the varicella zoster virus (human herpes virus 3).

• Shingles: Condition resulting from the reactivation of the same virus later in life, potentially triggered by factors like immune compromise.