What Is HIV and AIDS: Transmission, Progression, and Modern Treatment

This article is for informational purposes only. Consult a qualified healthcare professional for medical advice, diagnosis, or treatment.

Understanding HIV and AIDS

Human Immunodeficiency Virus (HIV) is a retrovirus that attacks the immune system, specifically targeting CD4+ T lymphocytes — white blood cells critical to orchestrating immune responses. If untreated, HIV progressively depletes these cells, leaving the body vulnerable to opportunistic infections and cancers. Acquired Immunodeficiency Syndrome (AIDS) is the most advanced stage of HIV infection, defined by a CD4 count below 200 cells per microliter of blood or the diagnosis of certain AIDS-defining conditions. As of 2023, approximately 39.9 million people worldwide were living with HIV, with sub-Saharan Africa bearing the highest burden.

The HIV Virus: Structure and Replication

HIV belongs to the lentivirus genus of retroviruses. Its outer envelope is studded with glycoprotein spikes (gp120 and gp41) that bind to CD4 receptors and co-receptors (CCR5 or CXCR4) on target cells. Once attached, HIV fuses with the cell membrane and injects its genetic material — two strands of RNA — along with viral enzymes. The viral enzyme reverse transcriptase converts the RNA into DNA, which is then integrated into the host cell's genome by the enzyme integrase. This integrated form, called the provirus, may remain dormant for years or begin producing new viral particles. A third enzyme, protease, cleaves newly made viral proteins into functional units needed to assemble infectious virions.

Modes of Transmission

HIV is present in blood, semen, pre-seminal fluid, rectal fluids, vaginal fluids, and breast milk. Transmission requires direct contact of these fluids with mucous membranes, damaged tissue, or bloodstream. The main routes include:

Sexual contact: Unprotected anal or vaginal sex is the most common route globally. Receptive anal sex carries the highest per-act risk (approximately 1.4% per act without a condom).
Sharing injection equipment: Sharing needles, syringes, or other drug-injection paraphernalia allows direct blood-to-blood transmission.
Mother-to-child transmission: HIV can pass from an infected mother to her child during pregnancy, labor, delivery, or breastfeeding. Without intervention, transmission rates reach 15–45%. Antiretroviral treatment reduces this to under 2%.
Blood transfusions and organ transplants: Screening programs have made this route extremely rare in countries with robust blood-supply oversight.

HIV is NOT transmitted through casual contact such as hugging, sharing food or utensils, insect bites, saliva, tears, or sweat.

Stages of HIV Infection

Stage	Characteristics	CD4 Count	Viral Load
Acute HIV Infection	Flu-like symptoms 2–4 weeks after exposure; highest infectivity	Drops sharply, then partially recovers	Very high
Chronic HIV Infection (Clinical Latency)	Few or no symptoms; may last 10+ years without ART	Gradual decline from ~500–1,200 cells/μL	Lower but detectable
AIDS	Severe immune deficiency; opportunistic infections and cancers appear	Below 200 cells/μL	Very high

Acute HIV Infection

Within 2–4 weeks of exposure, about 40–90% of people experience acute retroviral syndrome: fever, swollen lymph nodes, sore throat, rash, muscle aches, and fatigue. These symptoms resolve within weeks, but the person is highly infectious during this window. Standard HIV tests may return false negatives because the immune system has not yet produced detectable antibodies.

Chronic Infection and AIDS

Without treatment, chronic HIV infection gradually destroys CD4 cells. Once the count falls below 200/μL, the immune system can no longer defend against pathogens that healthy individuals easily fight off. AIDS-defining conditions include Pneumocystis jirovecii pneumonia, cytomegalovirus retinitis, toxoplasma encephalitis, Kaposi's sarcoma, and disseminated Mycobacterium avium complex.

Diagnosis

HIV testing methods vary by the target and timing:

Antibody tests: Detect HIV antibodies in blood or oral fluid; most common and rapid. The window period (time to detectable antibodies) is typically 23–90 days after exposure.
Antigen/antibody combination tests (4th generation): Detect both HIV antibodies and p24 antigen (a viral protein), shortening the window period to 18–45 days.
Nucleic acid tests (NAT): Detect viral RNA directly; can identify HIV as early as 10–33 days post-exposure; used for early diagnosis and monitoring.

Test Type	Window Period	Use Case
Rapid antibody test	23–90 days	Community screening, self-testing
4th-generation combo test	18–45 days	Clinical diagnosis
Nucleic acid test (NAT)	10–33 days	Early detection, blood supply screening
CD4 count	Not a diagnostic test	Monitor immune status
Viral load (HIV RNA)	Not a diagnostic test	Monitor treatment response

Antiretroviral Therapy (ART)

ART is the cornerstone of HIV treatment. It consists of combinations of antiretroviral drugs that target different steps in the HIV replication cycle, suppressing viral replication to undetectable levels. ART does not cure HIV but allows people to live long, healthy lives and prevents transmission. The principle of treatment: HIV quickly mutates and can develop resistance to a single drug, so combination therapy (previously called HAART — Highly Active Antiretroviral Therapy) is required.

Major drug classes include:

Nucleoside/Nucleotide Reverse Transcriptase Inhibitors (NRTIs): Block reverse transcriptase by competing with natural nucleotides (e.g., tenofovir, emtricitabine)
Non-Nucleoside Reverse Transcriptase Inhibitors (NNRTIs): Bind directly to reverse transcriptase and block its function (e.g., efavirenz, rilpivirine)
Integrase Strand Transfer Inhibitors (INSTIs): Block the integrase enzyme, preventing viral DNA from integrating into the host genome (e.g., dolutegravir, bictegravir) — now preferred in first-line regimens
Protease Inhibitors (PIs): Block viral protease, preventing maturation of new virus particles (e.g., darunavir)
Entry/Fusion Inhibitors: Block HIV from entering CD4 cells (e.g., maraviroc, enfuvirtide)

Prevention Strategies

Multiple evidence-based strategies exist to prevent HIV transmission:

Condoms: Male latex condoms, when used consistently and correctly, reduce HIV transmission by approximately 90–95%.
Pre-Exposure Prophylaxis (PrEP): Daily oral medication (tenofovir/emtricitabine) for HIV-negative individuals at high risk reduces sexual transmission by up to 99% with consistent use.
Post-Exposure Prophylaxis (PEP): A 28-day course of ART taken within 72 hours of potential exposure can prevent infection.
Undetectable = Untransmittable (U=U): Studies such as PARTNER and HPTN 052 conclusively demonstrate that people on effective ART with an undetectable viral load cannot sexually transmit HIV.
Harm reduction: Clean needle and syringe programs, opioid substitution therapy, and supervised consumption facilities reduce transmission among people who inject drugs.

Global Progress and Challenges

The UNAIDS 95-95-95 targets aim for 95% of people living with HIV to know their status, 95% of those diagnosed to be on ART, and 95% of those on ART to have viral suppression by 2025. As of 2023, global progress stands at approximately 86-89-93. Access to testing and treatment remains unequal across regions. Stigma, discrimination, and criminalization of key populations continue to impede progress. Despite these challenges, AIDS-related deaths have fallen by 69% since their peak in 2004, representing one of the most significant public health achievements of the modern era.