HIV

HIV is a retrovirus with an outer envelope containing gp20 and gp41. It's capsid is composed of p24, and contains RT (Reverse Transcriptase), Protease, Integrase, and 2 RNA strands. The p24 is what is tested for a diagnosis.

It's transmitted via:

• Contact of bodily fluids e.g. blood, breastmilk, vaginal secretions, and semen

• Vertical from mother to child

  • The risk of transmission is increased with Unprotected sex (anal sex is the highest risk), STI’s, IVDU, transfusions, needle-stick injuries

Early diagnosis and treatment is crucial as, when on ART with a low viral load, patients will have a very low chance of transmitting it to their sexual partners.

Life Cycle

1st phase - Attachment and Entry - Involves CD4 receptors, gp120, gp41, and CCR5/CXCR4 co-receptors

• Fusion/Entry inhibitors act here

2nd phase - Reverse transcription and Integration - Involves RT and Integrase

• RT Inhibitors and Integrase inhibitors act here

3rd phase - Transcription and Translation - Involves Protease

• Protease inhibitors act here

4th phase - Assembly and Budding

Investigations

Tests available:

• At-home test

• Nucleic Acid Test (NAT) - Also used to screen newborns

• ELISA - Tests for presence of HIV antibody and p24

• Rapid point-of-care - Finger-prick/Mouth swab, but a serological confirmation is still needed

Important investigations to do are Viral load and CD4 count!

Management

ART!

• Backbone of 2 different NRTIs (nucleotide RT inhibitors) + 1 drug of choice (options include protease/integrase inhibitors, and non-NRTIs)

N.B. ART = Antiretroviral therapy. ART is given to all patients, irrespective of viral load or CD4 count.

Prevention

• Barrier protection

• Pre-exposure Prophylaxis (PrEP) - Use of ART in those at high risk of acquiring HIV

• Post-exposure Prophylaxis (PEP) - Short-term use (up to 72hrs) of ART after potential exposure

• ART for all pregnant women with HIV - To prevent vertical transmission

AIDS (Acquired Immunodeficiency Syndrome)

This is an advanced stage of HIV where there’s evidence of an AIDS-defining illness + CD4 count < 200.

The main AIDS-defining illnesses to know include:

• Pneumocystis pneumonia (PCP) - fungal infection, commonly affecting lungs

  • Always have this as a differential in any immunocompromised patient presenting with a persistent dry cough and oxygen desaturation on minimal exertion.

  • Patients are given prophylaxis with Co-trimoxazole (Septrin)

• Kaposi’s sarcoma - most common tumour in HIV

• TB,

  CMV infection Lymphoma, Candidiasis, Toxoplasmosis, Cryptococcosis (fatal fungal pneumonia or meningitis), Cryptosporidiosis

Other less common AIDS-defining illnesses are CMV infection Lymphoma, Candidiasis, Toxoplasmosis, Cryptococcosis (fatal fungal pneumonia or meningitis), and Cryptosporidiosis.