# Human Immunodeficiency Virus (HIV) An overview of the Human Immunodeficiency Virus (HIV), its structure, life cycle, the disease it causes (AIDS), and methods of treatment and prevention. ## Introduction to HIV - **Human Immunodeficiency Virus (HIV):** The causative agent of **Acquired Immunodeficiency Syndrome (AIDS)**. - It is a **retrovirus**, meaning it uses its RNA genome to synthesize a DNA intermediate in the host cell. - First identified in 1984 and officially named HIV in 1986. ## Structure of HIV HIV is a spherical virus with a complex structure. - **Envelope:** An outer lipoprotein envelope derived from the host cell's membrane during budding. - **Glycoprotein Spikes:** Embedded proteins crucial for infection. - **gp120:** Outer glycoprotein that attaches to CD4 receptors on host cells. - **gp41:** Transmembrane glycoprotein critical for fusing the viral envelope with the host cell membrane. - **Matrix:** A protein shell located between the envelope and the capsid. - **Capsid:** A conical-shaped protein coat composed of capsomeres. - **Viral Core:** Contains the essential components for replication. - **Genetic Material:** Two single strands of viral RNA. - **Enzymes:** - **Reverse Transcriptase:** Converts the viral RNA genome into a complementary DNA (cDNA) molecule. - **Integrase:** Incorporates the viral DNA into the host cell's DNA. - **Protease:** Cleaves large viral proteins into smaller, functional units for new virion assembly. ## Life Cycle of HIV HIV exhibits host cell specificity, primarily targeting cells with CD4 receptors, such as Helper T-cells, macrophages, and some brain cells. 1. **Attachment (Adsorption):** The viral glycoprotein gp120 binds to the CD4 receptor on the surface of a host cell (e.g., a Helper T-cell). 2. **Penetration and Uncoating:** The viral envelope fuses with the host cell membrane, a process mediated by gp41. The virion enters the cell via endocytosis, and its capsid breaks down (uncoating), releasing the viral RNA and enzymes into the cytoplasm. 3. **Reverse Transcription:** The enzyme reverse transcriptase synthesizes a single strand of DNA (cDNA) complementary to the viral RNA. 4. **RNA Degradation:** The original viral RNA template is degraded by the enzyme ribonuclease (RNAase). 5. **DNA Replication:** The single-stranded cDNA is replicated to form a double-stranded viral DNA molecule. 6. **Integration:** The enzyme integrase incorporates the double-stranded viral DNA into the host cell's own DNA. 7. **Provirus Stage:** The integrated viral DNA is now called a **provirus**. It can remain dormant or become active. 8. **Transcription:** The host cell's RNA polymerase transcribes the proviral DNA, producing viral mRNA and new copies of the viral RNA genome. 9. **Biosynthesis (Translation):** Host cell ribosomes translate the viral mRNA into large viral proteins. 10. **Cleavage:** The enzyme protease cuts these large proteins into smaller, functional structural proteins and enzymes. 11. **Maturation (Assembly):** New viral RNA genomes and proteins assemble into new, immature virions. 12. **Release:** Mature virions are released from the host cell by budding, taking a portion of the host's cell membrane with them to form their own envelope. This process gradually depletes the host cell's membrane, rendering it non-functional and eventually killing it. ## Pathogenesis: How HIV Causes AIDS - **Helper T-cells** are crucial components of the immune system; they activate B-cells (to produce antibodies) and cytotoxic T-cells (to kill infected cells). - By targeting and destroying Helper T-cells, HIV systematically weakens the immune system. - The progressive decline in Helper T-cell count leads to a state of immunodeficiency, which is why the virus is named **Human Immunodeficiency Virus**. ## Symptoms and Stages of AIDS An HIV infection progresses through three main stages: | Stage | Name | Key Characteristics | | :--- | :--- | :--- | | **1** | **Asymptomatic Carrier** | Initial flu-like symptoms (fever, chills, rash) may appear and then disappear. The person often has no other symptoms for months or years. The individual is **highly infectious**. Blood tests for HIV antibodies become positive. | | **2** | **AIDS-Related Complex (ARC)** | Persistent swollen lymph glands (neck, armpits, groin). Other symptoms include night sweats, persistent cough, persistent diarrhea, memory loss, and depression. | | **3** | **Full-Blown AIDS** | The final and most severe stage. Characterized by a severely compromised immune system. Leads to severe weight loss, weakness, and the development of **opportunistic diseases**. | ## Opportunistic Diseases - These are infections caused by pathogens that a healthy immune system would normally fight off. - In AIDS patients, these pathogens take advantage of the weakened immune system. - Examples include: - **Skin Cancer** (e.g., Kaposi's Sarcoma) - Fungal infections (e.g., Pneumocystis pneumonia, candidiasis) - Viral infections (e.g., Cytomegalovirus) - Gastrointestinal, respiratory, and nervous system diseases. ## Treatment and Control ### Treatment of AIDS - **Antiretroviral Therapy (ART):** A combination of medicines used to fight HIV infection. - **Function:** ART is **not a cure** but can control the virus, allowing an HIV-positive person to live a longer, healthier life. It also reduces the risk of transmission. - **Limitations:** Can have toxic side effects, is costly, and requires strict daily adherence. A cure remains a major research goal. ### Control Measures and Prevention Prevention focuses on stopping the transfer of body fluids (blood, semen, etc.) from an infected person to an uninfected one. **Do:** - Use properly sterilized surgical instruments. - Screen all blood for HIV before transfusion. - Follow Islamic teachings and refrain from immoral sexual activities. **Do Not:** - Use or share used syringes and needles. - Share personal items like toothbrushes, blades, or towels. - An HIV-positive mother should not breastfeed her baby. **HIV is NOT Transmitted By:** - Shaking hands, hugging, coughing, or sneezing. - Swimming in the same pool. - Inanimate objects like toilets, doorknobs, or telephones. - Mosquitoes or other insects.