Herpesviruses, Poxviruses, & Human Papilloma Virus Study Notes

Herpesviruses, Poxviruses, & Human Papilloma Virus

Introduction

  • The chapter focuses on viruses that predominantly cause skin lesions.
  • Key herpesviruses discussed include Herpes Simplex Viruses (HSV) 1 and 2, Varicella-Zoster Virus (VZV), Cytomegalovirus (CMV), Epstein-Barr Virus (EBV), Human Herpesvirus 6, and Human Herpesvirus 8 (linked to Kaposi's Sarcoma).
  • Poxviruses such as Smallpox Virus and Molluscum Contagiosum Virus are also detailed.
  • Human papillomavirus (HPV) is covered as well.
  • Skin lesions manifest in different forms depending on the causative virus, with all viruses in this content having a DNA genome.

Herpesviruses

Overview
  • General Characteristics:
    • All herpesviruses contain linear double-stranded DNA.
    • They possess an icosahedral structure surrounded by a lipoprotein envelope.
    • The virions are typically large (120-200 nm) and replicate in the nucleus of the host cell.
    • They establish lifelong latent infections.
Types of Herpesviruses

  1. Herpes Simplex Virus (HSV):

    • Subtypes: HSV-1 & HSV-2
    • Transmission:
      • HSV-1: Primarily transmitted via saliva.
      • HSV-2: Transmitted through sexual contact.
    • Clinical conditions caused:
      • HSV-1: Gingivostomatitis, R oral labialis (cold sores), Keratitis, Encephalitis.
      • HSV-2: Genital herpes, neonatal herpes, Meningitis.

  2. Varicella-Zoster Virus (VZV):

    • Causes chickenpox and shingles.

  3. Cytomegalovirus (CMV):

    • Primarily affects immunocompromised individuals and newborns.

  4. Epstein-Barr Virus (EBV):

    • Associated with mononucleosis and certain types of cancers.

  5. Human Herpesvirus 6 & 7 (HHV-6, HHV-7):

    • Known for causing roseola in infants.

  6. Human Herpesvirus 8 (HHV-8):

    • Associated with Kaposi's sarcoma in HIV-positive patients.
Key Features of Skin Lesions
  • Typical Lesions:
    • HSV lesions appear as vesicles filled with serous fluid that eventually rupture.
    • VZV: Chickenpox and shingles exhibit vesicular rashes.
    • Poxviruses, like Smallpox, caused pustules (smallpox has been eradicated).
    • HPV causes warts and papillomas on skin and mucous membranes.
Properties and Structure
  • Genome:
    • All discussed viruses have a DNA genome.
  • Nucleocapsid Type:
    • Herpesviruses: Icosahedral with an envelope.
    • Poxviruses: Complex structure with an envelope.
Pathogenesis & Immunity
  • HSV enters through mucosal surfaces and infects epithelial cells.
  • The virus then infects neurons, establishing latency in sensory ganglion cells.
  • Reactivation can occur due to stress, hormonal changes, etc.
Transmission and Epidemiology
  • HSV-1 primarily transmitted via saliva; lesions commonly on the face.
  • HSV-2 transmitted through sexual contact; lesions mainly genital.
  • Asymptomatic shedding of both HSV types can occur, contributing to transmission.

Poxviruses

Smallpox Virus
  • Causes: Smallpox results in pustules and has been eradicated globally.
  • Molluscum Contagiosum Virus:
    • Causes fleshy papules on the skin, more prevalent in children and immunocompromised individuals.

Human Papillomavirus (HPV)

  • Causes growths on skin and mucous membranes, including warts and cervical dysplasia.
Summary of Organisms
  • Table 37-1 illustrates features of skin lesions caused by herpesviruses, poxviruses, and HPV.
  • Table 37-2 provides a detailed comparison of viral properties (such as virus family, genome structure, and nucleocapsid).
  • Importance of diagnostic techniques (PCR, cultures) and antiviral therapies such as Acyclovir is discussed.

Clinical Features

  • Each virus presents unique clinical features, including potential complications like encephalitis or neonatal disease.
  • Infection rates and immune responses vary among individuals, highlighting the importance of prevention and control measures.

Self-Assessment Questions

  • Review questions provide opportunities for further study and consolidation of key knowledge.

Practice Questions: USMLE & Course Examinations

  • Examples help in assessing understanding and application of content learned in the chapter.