HIV / AIDS in depth.

Overview

HIV (Human Immunodeficiency Virus) is a retrovirus that progressively destroys CD4+ T lymphocytes — the key coordinators of the immune response — leaving the body unable to fight infections and cancers. HIV infects approximately 1.3 million new people per year and approximately 39.9 million people live with HIV globally as of 2023. Antiretroviral therapy (ART) has transformed HIV from an invariably fatal infection to a manageable chronic condition, allowing people with HIV on treatment to live near-normal lifespans. However, an estimated 9.3 million people still lack access to treatment, and 630,000 died of AIDS-related illnesses in 2023.

AIDS (Acquired Immunodeficiency Syndrome) is the advanced stage of HIV infection, defined clinically by a CD4 count below 200 cells/mm³ or the presence of an AIDS-defining condition. Without ART, HIV progresses to AIDS in an average of 10 years. With ART initiated early, most people with HIV never develop AIDS. The scientific concept of U=U (Undetectable = Untransmittable) — confirmed definitively by the PARTNER2 study — means people on ART with undetectable viral load cannot sexually transmit HIV, fundamentally changing the epidemic's calculus.

History & Origin

HIV originated from cross-species transmission (zoonosis) of Simian Immunodeficiency Virus (SIV) from chimpanzees to humans in the Congo Basin, probably in the 1920s–1930s. HIV-1 group M — responsible for the global pandemic — spread from Kinshasa along colonial transport networks. The AIDS epidemic was formally recognized in 1981 in the USA when the CDC reported unusual clusters of Pneumocystis pneumonia and Kaposi's sarcoma in young gay men. HIV was isolated by Françoise Barré-Sinoussi and Luc Montagnier in 1983 (Nobel Prize 2008).

The first ART drug, zidovudine (AZT), was approved in 1987. The 1996 introduction of combination antiretroviral therapy (HAART) produced a dramatic reduction in AIDS mortality in countries with access. However, Sub-Saharan Africa — where 70% of people with HIV live — had essentially no access to ART until generic production was enabled by the Doha Declaration (2001) and the US President's Emergency Plan for AIDS Relief (PEPFAR, 2003).

Transmission

HIV is present in high concentrations in blood, semen, pre-seminal fluid, rectal fluids, vaginal fluids, and breast milk. Transmission requires contact between these fluids and mucous membranes, damaged tissue, or direct injection into the bloodstream.

• Sexual transmission: Unprotected anal sex (highest risk — receptive partner ~1.4% per act); unprotected vaginal sex; risk amplified by concurrent STIs (which cause genital ulcers or inflammation).
• Injection drug use: Sharing needles, syringes, or other drug paraphernalia with an HIV-positive person.
• Mother-to-child (MTCT): During pregnancy, labor/delivery, or breastfeeding. Without ART, transmission rate is 15–45%. With maternal ART + infant prophylaxis, risk is <1%.
• Blood transfusion/organ transplant: Risk near-zero in countries with universal blood screening.
• Healthcare/occupational: Needlestick injury from HIV-positive source; transmission risk ~0.3% per exposure.
• HIV is NOT transmitted through: air, water, saliva, tears, sweat, insect bites, sharing food/drink, toilet seats, or casual contact.

Clinical Stages

Diagnosis

• 4th generation HIV tests (antigen/antibody combination): Detects both HIV antibodies AND p24 antigen; turns positive at 18–45 days post-exposure. Standard of care in most high-income countries.
• Rapid HIV tests: Results in 20–30 minutes; blood or oral fluid; sensitivity >99%; widely used in resource-limited settings and community testing. Reactive result requires confirmatory test.
• HIV RNA (viral load) PCR: Detects HIV RNA; turns positive 10–12 days post-exposure; used for diagnosis in acute infection, infants, and monitoring treatment.
• CD4 count: Not a diagnostic test but critical for staging and treatment decisions. CD4 <200 = AIDS; CD4 <500 = immunocompromised; target on ART: >500 cells/mm³.
• HIV drug resistance testing: Genotypic or phenotypic resistance testing guides ART selection in treatment-naive patients in high-prevalence resistance settings, and in all patients failing first-line therapy.
• WHO recommends: All individuals be tested for HIV at least once in lifetime; annual testing for high-risk groups; self-testing kits now widely available.

Treatment — Antiretroviral Therapy (ART)

ART consists of combinations of antiretroviral drugs from different classes that suppress HIV replication. WHO recommends initiating ART in ALL people with HIV regardless of CD4 count — as soon as possible after diagnosis.

WHO-Recommended First-Line Regimens (2023)

• Dolutegravir (DTG) + lamivudine (3TC) + tenofovir (TDF or TAF): Preferred first-line globally — high barrier to resistance, once-daily, well-tolerated, available as single-tablet regimen (e.g., Triumeq DS, generic equivalents). DTG-based regimens achieve viral suppression in 90%+ of patients.
• Long-acting injectable ART: Cabotegravir + rilpivirine (Cabenuva) — approved in USA/Europe; given as monthly or 2-monthly injections; eliminates daily pill burden; highest adherence rates ever recorded in HIV trials.
• Children under 4 weeks: Zidovudine (AZT) + lamivudine (3TC) + nevirapine for prophylaxis; DTG-based regimens from age 4 weeks.

Treatment Monitoring

• Viral load: Target: undetectable (<50 copies/mL); check at 6 months, then every 12 months if suppressed
• CD4 count: Less critical once viral load undetectable; monitor annually or as clinically indicated
• Treatment failure: Viral load >1000 copies/mL on ART = treatment failure; conduct adherence counseling and resistance testing before switching

Prevention

• ART (Treatment as Prevention / TasP): Treating people with HIV suppresses viral load to undetectable — U=U means zero transmission risk sexually.
• PrEP (Pre-Exposure Prophylaxis): Daily tenofovir/emtricitabine (Truvada, Descovy) or on-demand dosing (2-1-1 schedule) for HIV-negative high-risk individuals; >99% effective when taken as prescribed. Long-acting injectable cabotegravir PrEP (every 2 months) now available in some countries.
• PEP (Post-Exposure Prophylaxis): 28-day course of ART started within 72 hours of potential HIV exposure; reduces transmission risk by >80%; used after needlestick injuries, sexual assault, or unprotected sex.
• Condoms: Consistent and correct use of male condoms reduces HIV transmission by ~85%.
• VMMC (Voluntary Medical Male Circumcision): Reduces HIV acquisition risk in heterosexual men by ~60%; WHO-recommended in high-prevalence African settings.
• PMTCT: Prevention of mother-to-child transmission — ART for HIV-positive pregnant/breastfeeding women + infant prophylaxis + early infant diagnosis; eliminates vertical transmission when fully implemented.
• Harm reduction: Needle/syringe exchange programs; opioid substitution therapy; naloxone distribution — critical for people who inject drugs.
• Vaccines: No approved HIV vaccine exists. The RV144 trial (Thailand, 2009) showed 31% efficacy with ALVAC/AIDSVAX, the only positive HIV vaccine trial. Multiple candidates in trials including mRNA-based vaccines, mosaic vaccines (HVTN 702, discontinued), and broadly neutralizing antibodies.

Global Impact

The AIDS pandemic has killed approximately 40 million people since the 1980s. As of 2023, 39.9 million people live with HIV; 77% know their status; 76% are on ART; and 71% have achieved viral suppression. Sub-Saharan Africa bears 65% of the global burden. UNAIDS targets — 95-95-95 by 2025 (95% of people with HIV knowing their status, 95% on treatment, 95% virally suppressed) — are within reach in some regions but remain far off in others.

PEPFAR (US President's Emergency Plan for AIDS Relief) has provided ART to over 20 million people since 2003 — the largest disease-specific global health program in history, credited with saving 25+ million lives. The Global Fund to Fight AIDS, Tuberculosis and Malaria has disbursed over $60 billion since 2002. Despite this progress, 630,000 people died of AIDS-related illnesses in 2023, and 1.3 million acquired HIV — far from the targets needed to end AIDS as a public health threat by 2030.

Frequently Asked Questions

Sources & Citations