Hepatitis B Virus Overview

Viral Infectious Agents

•  Viral infectious agents are a topic covered in block 1.2 lectures.
•  The lecture notes are from the 2024-2025 academic year.
•  Lecture notes are by Mohammed Alibrahem and Arwa Alzaid.
•  Note-taking highlighters are used to organize the information.

Herpes Simplex Viruses (HSV) Type 1

• Herpesviridae viruses are known for latent sequences in their pathogenesis.
• HSV is one example of a virus with latent viral infection.
• Primary HSV infection occurs upon first exposure, usually in children.
•  Transmission is typically by direct contact (e.g., saliva, tears)
•  Clinically, primary infection presents as vesicles on erythematous bases.
•  Vesicles rupture and dry, forming crusts that heal without scarring within 7-10 days.
•  This differs from other viruses that heal with scarring.

Clinical Types of HSV-1 Infection

• The commonest type of primary HSV-1 infection is acute gingivostomatitis.

Pathogenesis & Clinical Picture: Secondary Infection

• Latent infections are present in the dorsal root ganglion of the face (trigeminal ganglion) in HSV-1.
• Virus particles are transported along axons to the sensory dorsal root ganglion.
• Some virus particles establish latent infection.
• HSV-1 latency is in the trigeminal ganglion and lasts the lifetime of the host.
• Reactivation can occur every 2-3 years due to stressful conditions and the host's immune status.

Recurrent Herpes Labialis

• Recurrent herpes labialis (fever blisters or cold sores) is a result of reactivation of primary gingivostomatitis.
• This can occur when immune status is lower.

Varicella-Zoster Virus (VZV)

• VZV infection has two clinical forms:

  • Primary infection: varicella (chickenpox). This is characterized by a generalized eruption.
  • Reactivation infection: zoster (shingles). This infection causes a localized form.

Chickenpox (Varicella): Primary Infection

• This is usually seen in children aged 4-10.
• Droplet infection is the main transmission route.
• Approximately 90% of adults have been infected in childhood, but 10% remain susceptible.

Shingles (Zoster): Reactivation

• This occurs in adults.
• This results from the reactivation of a latent varicella infection in neurons.
• The virus travels to the ganglion via the periphery along nerve axons or blood during the viraemic stage of varicella infection from childhood.

Varicella Rash: Clinical features

• The rash starts on the trunk, first, then spreads to the limbs. (Generalized).
• Initially, a macular rash becomes elevated above the skin as macules.
• These evolve into papules, then into vesicles filled with clear fluid.
• The filled vesicles then become pustules, that crust and eventually heal.
• Healing is without scarring.

Zoster Rash: Clinical Features

• The rash is unilateral or confined to limited areas on one side of the body,
• This is due to one dermatome being affected.
• The rash is characterized by painful vesicular eruptions.
• This is important to know so that professionals can pinpoint the affected nerve.

Laboratory Diagnosis

• Smears of vesicular lesions and direct virus detection.
• Serology — detecting specific VZV antibodies (IgM or rising IgG titre) using ELISA.

Poxviridae Family

• The poxviruses are the largest of all viruses.
• They are large enough that they can be seen with a light microscope (300nm)
• They are brick-shaped with complex symmetry.
• Poxvirues are enveloped viruses with double-stranded DNA.
• Smallpox was once of medical importance but is now eradicated.

Hepatitis B Virus (HBV)

• HBV is a DNA virus of the Hepadnaviridae family.
• It causes serum hepatitis.
• The complete virus particle is called a Dane particle.
• Diagnosis can be confirmed by various means.
• HBV is spherical or tubular, which is caused by the surface antigen HBsAg
• HBV can be transmitted sexually, parenterally, from mother to infant, and through various other contacts.

HIV

• HIV is an enveloped virus.
• It is easily disinfected once outside the host.
• It enters the blood to infect.
• HIV has various structures, such as a glycoprotein complex made from gp120 and gp41.

HIV Structure and Genome

• HIV has a core and a capsid.
• The HIV genome is made up of two identical copies of positive-sense, single-stranded RNA.

HIV Transmission

• HIV can be transmitted sexually.
• It can be transmitted by blood or blood products.
• It can sometimes be transmitted during pregnancy or through breastfeeding.

HIV Diagnosis

• Antibody screening tests are used to determine HIV infection.
• An initial positive test often requires confirmatory tests such as western blot testing.

Further testing for HIV

• Nucleic acid tests – e.g., PCR
• CD4 counts are used to determine the progression and stage of the infection.