Introduction
HIV (Human Immunodeficiency Virus) is the virus that causes AIDS (Acquired Immunodeficiency Syndrome). HIV weakens the immune system by destroying CD4+ T cells, which are essential for fighting infections. A person is diagnosed with AIDS when the CD4 count falls below 200 cells/µL or when certain opportunistic infections or cancers appear.
HIV infects humans only. Being a virus, it can survive and multiply only by entering and taking control of host cells. HIV is present in several body fluids—blood, semen, vaginal secretions, breast milk—and is transmitted mainly through unprotected sexual contact, infected needles, blood products or from mother to baby. HIV cannot be transmitted through casual contact, mosquito bites or tears and urine because the viral levels are too low.
Structure of HIV
HIV is a spherical, enveloped virus belonging to the Lentivirus subfamily of retroviruses. It is about 100–120 nm in diameter, much smaller than a red blood cell.
- It contains two single strands of viral RNA in the core.
- The outer envelope contains lipid layers with glycoprotein knobs.
- Envelope proteins (gp120 and gp41) help the virus attach and enter human cells.
Important Structural Proteins
- gp120: External glycoprotein responsible for attachment to CD4 receptors.
- gp41: Transmembrane protein helping viral fusion with host cells.
- p17 (matrix): Inside the envelope, provides structural support.
- p24 (capsid): Forms the core capsule holding viral RNA.
Major HIV Genes
1. Gag (Group Specific Antigen)
Codes for internal structural proteins such as p17 and p24.
2. Env (Envelope)
Codes for gp160 which breaks into gp120 and gp41—important for viral entry.
3. Pol (Polymerase)
Codes for enzymes such as:
- Reverse transcriptase (p66, p51)
- Integrase (p31)
- Protease
These enzymes help HIV convert RNA to DNA, integrate into host DNA and complete viral replication.
Pathophysiology
HIV enters the body and begins rapid replication. Viral levels in blood become extremely high during early infection. CD4 count drops sharply.
Acute Phase
- HIV multiplies fast → high viral load.
- CD4 count falls due to viral killing and cytotoxic T cell activity.
- CD8 cells control the virus but cannot eliminate it completely.
- Patients seroconvert (produce antibodies) within weeks.
Chronic Phase
- HIV continues slow replication for years.
- CD4 count gradually drops.
- Generalized immune activation and inflammation occur.
- Intestinal mucosa loses large numbers of CD4 cells due to high CCR5 expression.
Late Phase (AIDS)
When CD4 count drops below 200 cells/µL, the patient becomes highly vulnerable to life-threatening infections and cancers.
Modes of Transmission
1. Sexual Transmission
Most common method. Unprotected vaginal, anal or oral sex with an infected person increases risk. Other STDs like syphilis and gonorrhea further increase transmission risk.
2. Blood and Blood Products
- Shared needles in IV drug use
- Needlestick injuries in healthcare settings
- Transfusion of unscreened blood
3. Mother to Child Transmission
Occurs during pregnancy, childbirth or breastfeeding. Without treatment, risk is 20–35%. Depends on mother’s viral load and CD4 count.
4. Contaminated Clotting Factors
Seen in hemophilia patients receiving unscreened clotting factor products.
5. Organ or Tissue Transplantation
Rare due to strict donor screening.
Primary HIV Syndrome
A flu-like illness appears 2–6 weeks after infection. Symptoms include:
- Fever
- Sore throat
- Headache
- Body rash
- Diarrhea
- Fatigue
- Joint and muscle pain
- Lymph node swelling
After this stage, HIV becomes silent (asymptomatic phase) for years while CD4 count slowly falls.
Opportunistic Infections
When CD4 count falls below 500, infection risk increases. Below 200 cells/µL, patient is diagnosed with AIDS.
Common Symptoms of Opportunistic Infections
- Chronic cough or breathlessness
- Painful swallowing
- Persistent diarrhea
- White patches in mouth
- Pneumonia-like symptoms
- Fevers lasting weeks
- Vision problems
- Nausea and vomiting
- Skin rashes or blotches
- Seizures or lack of coordination
- Memory loss and confusion
CD4 Count < 50 Cells/µL
Risk of severe illnesses increases:
- Persistent shingles
- Oral candidiasis
- Kaposi’s sarcoma
- Mycobacterium avium infection
- Cytomegalovirus (retinitis)
- Lymphoma
- HIV-associated dementia
HIV in Infants
- Failure to thrive
- Oral thrush
- Hepatosplenomegaly
- Lymph node enlargement
- Frequent diarrhea
- Recurrent bacterial infections
- Neurological abnormalities
Diagnosis
HIV tests detect antibodies, antigens or viral genetic material.
1. Antibody Tests
Most common screening method.
ELISA
First-line test using blood, oral fluid or urine. Positive results require confirmation.
Western Blot
Confirmatory test—detects antibodies against specific HIV proteins.
2. Antigen Test
Detects HIV p24 antigen 1–3 weeks after infection. Useful for early diagnosis.
3. PCR Test (Polymerase Chain Reaction)
- Detects HIV RNA directly.
- Can diagnose infection within 2–3 weeks.
- Used for infants because maternal antibodies make antibody tests unreliable.
Therapeutic Approach
There is no cure for HIV, but antiretroviral therapy (ART/HAART) suppresses viral replication and improves immunity.
Drug Classes
1. NNRTIs (Non-Nucleoside Reverse Transcriptase Inhibitors)
- Efavirenz
- Etravirine
- Nevirapine
2. NRTIs (Nucleoside Reverse Transcriptase Inhibitors)
- Abacavir
- Lamivudine + Zidovudine
- Emtricitabine + Tenofovir
3. Protease Inhibitors
- Atazanavir
- Darunavir
- Ritonavir
- Fosamprenavir
4. Entry/Fusion Inhibitors
- Enfuvirtide
- Maraviroc
5. Integrase Inhibitors
- Raltegravir
Prevention
- Practice safe sex (condom use).
- Abstinence or delayed sexual activity reduces risk.
- Avoid sharing needles; use needle-exchange programs.
- Healthcare workers should follow universal precautions.
- Mother-to-child transmission can be prevented with ART.
- Avoid breastfeeding if HIV positive.
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