HIV and AIDS — Revision Notes

⚡ 30-Second Revision

Causative Agent: — HIV (Human Immunodeficiency Virus), a retrovirus.
Genetic Material: — Two identical ssRNA strands.
Key Enzymes: — Reverse transcriptase (RNA $\rightarrow$ DNA), Integrase (viral DNA into host DNA), Protease (cleaves viral polyproteins).
Target Cells: — CD4+ T-lymphocytes (Helper T-cells).
Transmission: — Unprotected sex, contaminated needles, mother-to-child (pregnancy, birth, breastfeeding).
NOT Transmitted By: — Casual contact, air, water, insect bites.
AIDS Definition: — CD4+ T-cell count < 200 cells/mm³ or presence of opportunistic infections.
Diagnosis: — ELISA (screening), Western Blot/PCR (confirmation).
Treatment: — ART (Antiretroviral Therapy) - suppresses viral replication, restores immune function, not a cure.

2-Minute Revision

HIV, a retrovirus, causes AIDS by progressively destroying CD4+ T-lymphocytes, critical cells of the immune system. Its unique replication cycle involves reverse transcriptase converting viral RNA into DNA, which then integrates into the host genome.

This leads to a gradual decline in immune function, making the body vulnerable to opportunistic infections and certain cancers, eventually leading to AIDS. Transmission occurs through specific bodily fluids like blood, semen, and breast milk, primarily via unprotected sexual contact, sharing contaminated needles, or from mother to child.

It is not spread through casual contact. Diagnosis involves screening tests like ELISA and confirmatory tests such as Western Blot or PCR. While there's no cure, Antiretroviral Therapy (ART) effectively manages the infection by suppressing viral replication, allowing individuals to live long, healthy lives and significantly reducing transmission risk.

Prevention focuses on safe practices and pre-exposure prophylaxis (PrEP).

5-Minute Revision

HIV (Human Immunodeficiency Virus) is a lentivirus, a type of retrovirus, characterized by its RNA genome and the enzyme reverse transcriptase. This enzyme allows HIV to convert its RNA into DNA, which then integrates into the host cell's genome, forming a provirus.

The primary target cells are CD4+ T-lymphocytes, crucial for coordinating immune responses. HIV's gp120 protein binds to the CD4 receptor and a co-receptor (CCR5/CXCR4) to enter these cells. Once inside, the virus replicates, eventually destroying the infected CD4+ T-cells.

This leads to a gradual decline in the CD4+ T-cell count, severely weakening the immune system. The final stage, AIDS (Acquired Immunodeficiency Syndrome), is diagnosed when the CD4+ count drops below 200 cells/mm³ or when opportunistic infections (e.

g., *Pneumocystis pneumonia*, Kaposi's sarcoma) or AIDS-defining cancers appear.

Transmission occurs through direct contact with specific bodily fluids: blood, semen, vaginal fluids, rectal fluids, and breast milk. Common routes include unprotected sexual intercourse, sharing contaminated needles, and mother-to-child transmission during pregnancy, childbirth, or breastfeeding.

HIV is NOT transmitted through casual contact, air, water, or insect bites. Diagnosis typically involves an initial screening with ELISA (detects antibodies/antigens), followed by a confirmatory test like Western Blot (detects specific antibodies) or PCR (detects viral RNA/DNA).

Treatment involves Antiretroviral Therapy (ART), a combination of drugs that inhibit different stages of the viral life cycle. ART suppresses viral load, restores immune function, prevents progression to AIDS, and significantly reduces transmission risk, though it is not a cure.

Prevention strategies include safe sex practices, sterile needle use, and pre-exposure prophylaxis (PrEP) for high-risk individuals.

Prelims Revision Notes

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HIV: The Virus

* Type: Retrovirus (specifically, a lentivirus). * Genetic Material: Two identical single-stranded RNA (ssRNA) molecules. * Structure: Enveloped virus with glycoproteins gp120 and gp41 on its surface.

Contains capsid, reverse transcriptase, integrase, and protease enzymes. * Key Enzymes: * Reverse Transcriptase: Converts viral RNA into DNA. * Integrase: Integrates viral DNA (provirus) into host cell's genome.

* Protease: Cleaves viral polyproteins into functional proteins during maturation. * Target Cells: Primarily CD4+ T-lymphocytes (helper T-cells), also macrophages, dendritic cells.

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HIV Life Cycle (Key Steps):

* Binding: gp120 binds to CD4 receptor and co-receptor (CCR5/CXCR4) on host cell. * Fusion: Viral envelope fuses with host cell membrane, releasing viral core. * Reverse Transcription: Viral RNA $\rightarrow$ Viral DNA (by reverse transcriptase).

* Integration: Viral DNA (provirus) integrates into host DNA (by integrase). * Replication: Host machinery transcribes/translates provirus into viral RNA/proteins. * Assembly & Budding: New virions assemble and bud off, maturing via protease activity.

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AIDS: The Disease Stage

* Definition: Acquired Immunodeficiency Syndrome, the final stage of HIV infection. * Criteria: CD4+ T-cell count < 200 cells/mm³ OR presence of AIDS-defining opportunistic infections (e.g., *Pneumocystis pneumonia*, Kaposi's sarcoma, certain types of tuberculosis) or cancers. * Pathogenesis: Progressive destruction of CD4+ T-cells leads to severe immunodeficiency.

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Transmission:

* Confirmed Routes: Unprotected sexual contact (vaginal, anal, oral), sharing contaminated needles/syringes, mother-to-child (during pregnancy, childbirth, breastfeeding), contaminated blood transfusions/organ transplants (rare now due to screening). * NOT Transmitted By: Casual contact (hugging, shaking hands), air, water, food, insect bites, toilet seats.

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Diagnosis:

* Screening Tests: ELISA (Enzyme-Linked Immunosorbent Assay) - detects HIV antibodies and/or antigens. Rapid HIV tests. * Confirmatory Tests: Western Blot (detects specific HIV antibodies), PCR (Polymerase Chain Reaction) - detects viral RNA/DNA (viral load), used for early detection, confirmation, and monitoring.

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Treatment & Prevention:

* Treatment: Antiretroviral Therapy (ART) - combination of drugs targeting different stages of HIV life cycle. Suppresses viral replication, restores immune function, prevents progression to AIDS. Not a cure. * Prevention: Safe sex practices (condoms), sterile needles, PrEP (Pre-Exposure Prophylaxis) for high-risk individuals, PEP (Post-Exposure Prophylaxis) after potential exposure, preventing mother-to-child transmission (ART for pregnant mothers, safe delivery, formula feeding).

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Key Terms: — Opportunistic infections, viral load, CD4 count, window period.

Vyyuha Quick Recall

HIV Invades Very Active Immune Defense Systems

HIV: Human Immunodeficiency Virus (the virus)
Invades: Integrase (enzyme that integrates viral DNA)
Very: Viral RNA (genetic material)
Active: AIDS (the disease stage)
Immune: Immunodeficiency (result of infection)
Defense: Decreased CD4+ T-cells (primary target)
Systems: Sex, Sharing needles, Secretions (transmission routes)