Viral Infections 2

Question 1

List the most clinically important types of blood-borne viral infection.

Answer 1

• HIV
• HCV (hep C)
• HBV (hep B)

Question 2

What are the most clinically important types of Herpesvirus infection?

Answer 2

• VZV
• HSV
• EBV
• CMV

Question 3

What are two types of HIV virus and describe the differences in their geographical distribution

Answer 3

1. HIV 1 - most common cause of HIV
   - found throughout the world
2. HIV 2 - it is less transmissible and causes a less severe infection
   - much less common than HIV 1
   - largley confined to West Africa

In general, over 2/3 of people living with hIV are in Sub-Saharan Africa

Question 4

Outline the lifecycle of the HIV virus in the human host

Answer 4

Lifecycle:

• HIV binds to the CD4 receptor on hosts T helper cell surfaces
• it transcribed its genomic RNA to DNA with reverse transcriptase
• the viral DNA is then integrated into human DNA
• The viral genes encode (transcribe) a variety of proteins, and new virions are produced.
• host cell dies

Question 5

Demonstrate why it is important to understand the HIV lifecycle to appreciate antiretroviral action

Answer 5

• The aim of HIV treatment is to suppress virological replication and allow recovery of the CD4 cell population.
• Antiviral meds include reverse transcriptase inhibitors, protease inhibitors, integrase inhibitors, and fusion inhibitors

Question 6

Describe the routes of transmission of HIV

Answer 6

Fluids that can transmit HIV:

• blood
• semen
• vaginal secretions
• breast milk

These must come in contact with a mucous membrane or damaged tissue, or be directly injected into the blood-stream for transmission to occur.

Most common methods of transmission:

• sexual
• mother to child
• sharing needles

Less common:

• oral sex
• exposure to infected vlood
• transfusion
• organ transplant

Question 7

Describe briefly the time course of HIV infection and the development of AIDS

Answer 7

1. Acute infection
   - 0-9 weeks
   - peak of HIV RNA copies in plasma, then sudden decrease before latency
   - CD4 lymphocyte count decreases and then starts to increase before latency
2. Clinical Latency
   - 9wks - 7 years
   - HIV RNA copies in plasma increases slowly over time
   - CD4 lymphocyte count increases for a bit and then decreases slowly over time
3. Symptomatic Infection
   - 7 years +
   - HIV RNA copies in plasma increases quicker
   - CD4 lymphocyte count continues to decrease

Median period for progression to AIDS is 10 years if not treated

Most infectious in early and late infection

Question 8

Name the main infectious and neoplastic conditions associated with AIDS

Answer 8

1. Opportunistic infections:
   - Pneumocystis pneumonia
   - tuberculosis
   - Progressive Multifocal Leukoencephalopathy
   - Cerebral toxoplasmosis
   - Cryptococcal infection
   - Cryptosporidiosis
   - Cytomegalovirus retinitis
   - Disseminated MAC (Mycobacterium avid complex)
2. Neoplasia:
   - Kaposi’s Sarcoma (proliferation of vascular structures within the skin, mucous membranes, and rarely organs.)
   - non-Hodgkin’s lymphoma
   - multiple myeloma
   - melanoma
   - solid organ cancers

Question 9

What are the stages of VZV (Varicella-Zoster virus)?

Answer 9

a) Primary infection - chicken pox (varicela)
b) Latent infection in dorsal root ganglia
c) Reactivation - shingles (zoster)

Question 10

Describe the pathogenesis and clinical features of shingles

Answer 10

Pathogenesis:
Shingles may occur when the immune system becomes less effective at containing the virus at its site of latency (dorsal root ganglion).
Viruses travel down the corresponding sensory nerve to produce a very painful eruption in the corresponding dermatome.

Clinical features:
Across one dermatome - rash which progresses from small fluid filled vesicles through to pustules and crusty