Human immunodeficiency virus (HIV)

Question 1

What is the aetiology of HIV? (x2 (x4))

Answer 1

• Sexual intercourse
• Blood and any other bodily fluids: mother to child (intrauterine, childbirth, breastfeeding), needles (IVDU, HCPs), blood product transfusion, organ transplantation

Question 2

What is the pathophysiology of HIV?

Answer 2

• Gains entry into cells by binding of its envelope glycoprotein (gp120) to CD4 receptor and co-receptor on T cells and macrophages
• It is a retrovirus, so uses transcribes its own reverse transcriptase to make a DNA copy of its RNA (found in the viral core). This enzyme is error-prone, so HIV mutation rate is high
• HIV DNA is incorporated into the host genome and dissemination of virions leads to T cell and macrophage depletion.
• During initial HIV infection, there is an immune response to HIV which curtails its replication and is believed to create an HIV load set point. The set point in an individual is a prognostic indicator of the disease

Question 3

What is the epidemiology of HIV: Transmission? Where?

Answer 3

Most commonly transmitted heterosexually worldwide, but more common in homosexuals in the West. On the rise in Africa and Asia.

Question 4

What is AIDS?

Answer 4

Syndrome of a constellation of infections, conditions, or malignancies that occur as a result of the increasing immune depletion that HIV infection incurs over time.

Question 5

What are the signs and symptoms of HIV: Three phases?

Answer 5

1. SEROCONVERSION (4-8 weeks post-infection): self-limiting fever, night sweats, generalised lymphadenopathy, sore throat, oral ulcers, rash, myalgia, encephalitis and diarrhoea
2. EARLY/ASYMPTOMATIC PHASE (18 months – 15 years duration): some may have persistent lymphadenopathy, progressive minor symptoms of rash, oral thrush and weight loss
3. AIDS: CD4 count is less than 200/mm^3

Question 6

What are the signs and symptoms of HIV: Direct effects of HIV? (x6)

Answer 6

• Neurological: polyneuropathy (note this can also be caused by some antiretroviral therapy), myelopathy, dementia
• Lung: lymphocytic interstitial pneumonitis
• Heart: cardiomyopathy, myocarditis
• Haematological: anaemia, thrombocytopenia
• GI: HIV enteropathy (malabsorption and diarrhoea), wasting
• Eyes: cotton wool spots

Question 7

What are the signs and symptoms of HIV: Secondary infections and malignancies arising from immunodeficiency? (x4 and x4)

Answer 7

• BACTERIAL: mycobacteria (lungs, GI, skin): Mycobacterium tuberculosis, avium intracellulare and staphylococci, Salmonella, capsulated organisms (Strep. pneumoniae, H. influenzae)
• VIRAL: CMV, HSV, VZV, HPV, papovavirus (progressive multifocal leukoencephalopathy with motor, intellectual and speech impairment), EBV
• FUNGAL: pneumocystis pneumonia, Cryptococcus (meningitis), Candida, invasive aspergillosis
• PROTOZOAL: toxoplasmosis, cryptosporidia and microsporidia
• TUMOURS: Kaposi’s sarcoma, SCC (particularly cervical or anal), non-Hodgkin’s B-cell lymphoma, Hodgkin’s lymphoma

Question 8

What is Kaposi’s sarcoma?

Answer 8

Cutaneous, mucosal or conjunctival vascular tumour caused by human herpesvirus (HHV8).

Question 9

What are the investigations for HIV? (x3)

Answer 9

• HIV ANTIBODY TEST with ELISA which should be confirmed with a second ELISA or Western blot. Can also do PCR for viral RNA.
• CD4 and HIV RNA VIRAL LOAD: CD4 count less than 200 defines AIDS, and viral load used to assess disease control
• CXR, CT, MRI, COLONSCOPY, BIOPSY: to monitor for secondary infections and malignancies