HIV/AIDS — Transmission, Antiretroviral Therapy, PrEP & Treatment Guide — Symptoms, Causes & Treatment | MyMedicPlus

Human immunodeficiency virus (HIV) is a retrovirus that targets CD4+ T-lymphocytes — the orchestrators of the adaptive immune response — progressively depleting these cells and impairing immunity. Without treatment, HIV leads to acquired immunodeficiency syndrome (AIDS), defined as a CD4 count below 200 cells/microL or the occurrence of an AIDS-defining illness (such as Pneumocystis pneumonia, Kaposi's sarcoma, or cryptococcal meningitis). Approximately 39.9 million people live with HIV globally. With modern antiretroviral therapy (ART), HIV is now a manageable chronic condition — people with HIV on effective treatment have a near-normal life expectancy, cannot sexually transmit the virus (Undetectable = Untransmittable, U=U), and experience minimal medication-related burden with once-daily single-tablet regimens. The global target remains elimination of HIV transmission by 2030 (UNAIDS 95-95-95 targets: 95% of people with HIV diagnosed, 95% on ART, 95% with undetectable viral load).

HIV-1 (the dominant global strain) and HIV-2 (predominantly West Africa, less pathogenic) are transmitted through specific body fluids: blood, semen (including pre-ejaculatory fluid), vaginal and rectal secretions, and breast milk. HIV is NOT transmitted through saliva, tears, sweat, casual contact, hugging, shared utensils, coughing, sneezing, insect bites, or water. Routes of transmission: sexual intercourse (highest risk — receptive anal intercourse 138 per 10,000 exposures; insertive anal 11/10,000; receptive vaginal 8/10,000; insertive vaginal 4/10,000); sharing needles or drug equipment; blood transfusions with unscreened blood; needle-stick injuries in healthcare workers (0.23% per exposure); and mother-to-child (vertical) transmission during pregnancy, delivery, or breastfeeding (reduced to below 1% with ART). High-risk populations: men who have sex with men (MSM — 60% of new HIV diagnoses in high-income countries); people who inject drugs; sex workers; transgender women; and sexual partners of HIV-positive individuals. HIV viral load is the strongest determinant of transmission risk — detectable viral load increases transmission probability by 35-fold compared to undetectable.

Acute HIV infection (seroconversion illness, 2-4 weeks after exposure): a flu-like syndrome affecting 50-70% of newly infected people — fever (typically above 38.5°C), pharyngitis, rash (maculopapular, centripetal distribution on trunk), lymphadenopathy, myalgia, arthralgia, headache, and oral ulcers. This resembles infectious mononucleosis and is often misdiagnosed. HIV RNA is very high during acute infection (millions of copies/mL), making this the most infectious phase. After acute illness: clinically asymptomatic chronic HIV infection — lasting years (average 8-10 years without treatment). Persistent lymphadenopathy may be present. As CD4 declines below 500 cells/microL: constitutional symptoms (weight loss, fatigue, night sweats, diarrhoea) and opportunistic infections begin to appear. AIDS (CD4 below 200/microL): Pneumocystis jirovecii pneumonia (PCP — progressive breathlessness, non-productive cough, low-grade fever, bilateral interstitial infiltrates on CXR); CNS toxoplasmosis (space-occupying lesion — ring-enhancing on CT/MRI); cryptococcal meningitis (CD4 below 100); CMV retinitis and colitis; disseminated Mycobacterium avium complex (MAC); cerebral lymphoma; and oesophageal candidiasis. AIDS-defining malignancies: Kaposi's sarcoma (HHV-8), primary CNS lymphoma, and invasive cervical cancer.

HIV testing: fourth-generation combined antigen/antibody immunoassay detects both HIV antibodies and p24 antigen — window period is 45 days after exposure for 99.9% sensitivity. A reactive screening test is confirmed by supplemental antibody differentiation assay (distinguishing HIV-1 from HIV-2). HIV RNA PCR (viral load): detects acute infection before antibody seroconversion (window period 10-14 days); quantifies viral replication and is the primary treatment monitoring tool. CD4 lymphocyte count: assesses immune status and guides prophylaxis decisions (CD4 below 200: start Pneumocystis prophylaxis — co-trimoxazole). Genotypic resistance testing: before starting ART to identify transmitted drug-resistant variants and guide regimen selection. Baseline investigations: full blood count, renal and liver function, HbA1c, lipid profile, urinalysis, hepatitis B surface antigen and anti-HBc, hepatitis C antibody, syphilis serology, gonorrhoea and chlamydia NAAT, and tuberculosis assessment (IGRA or TB NAAT). WHO recommends universal HIV testing for all adults attending healthcare in high-prevalence settings.

All HIV-positive individuals should start ART regardless of CD4 count — ideally on the day of diagnosis ('same-day ART start'). Modern first-line ART regimens consist of 2 or 3 antiretroviral drugs from different classes to suppress viral replication to below 50 copies/mL. Preferred first-line regimens: dolutegravir/lamivudine (Dovato — 2-drug regimen with high genetic barrier to resistance; suitable when pre-ART viral load below 500,000 copies/mL and no chronic active hepatitis B); bictegravir/tenofovir alafenamide/emtricitabine (Biktarvy — 3-drug once daily single tablet; excellent tolerability, high resistance barrier). Second-line alternatives: dolutegravir + tenofovir + lamivudine/emtricitabine; efavirenz-based regimens (still first-line in resource-limited settings where tenofovir/emtricitabine/efavirenz is the WHO-recommended option). Long-acting injectable ART: cabotegravir + rilpivirine IM injection every 4-8 weeks (Cabenuva) — eliminates daily pill burden; ideal for patients with adherence challenges or who prefer not to take daily pills. HIV Pre-exposure Prophylaxis (PrEP): oral tenofovir alafenamide/emtricitabine or tenofovir disoproxil/emtricitabine daily for HIV-negative individuals at high risk — reduces HIV acquisition by over 99% with consistent use; or injectable cabotegravir 600 mg IM every 2 months (HPTN 083 trial: 66% superior to oral PrEP in MSM). Post-exposure Prophylaxis (PEP): 28-day ART course started within 72 hours of high-risk exposure — the sooner started, the more effective. Opportunistic infection prophylaxis: co-trimoxazole when CD4 below 200 (prevents PCP and toxoplasmosis).

Without antiretroviral therapy (ART), HIV infection progresses to AIDS (CD4 count below 200 cells/mcL or the development of an AIDS-defining illness). AIDS-defining conditions include Pneumocystis jirovecii pneumonia (PCP — the most common opportunistic infection in high-income countries), cerebral toxoplasmosis (CD4 below 100), cytomegalovirus (CMV) retinitis causing blindness, cryptococcal meningitis, Mycobacterium avium complex (MAC) disseminated infection, and Kaposi's sarcoma. Progressive multifocal leukoencephalopathy (PML) from JC virus reactivation causes severe neurological decline. HIV-associated neurocognitive disorder (HAND) ranges from mild cognitive impairment to HIV dementia. Cardiovascular disease risk is increased 2-fold in people with HIV due to chronic immune activation, dyslipidaemia from antiretroviral therapy, and higher rates of smoking. Non-AIDS-defining cancers — particularly non-Hodgkin lymphoma, anal cancer, and lung cancer — are significantly more common. HIV wasting syndrome (unintentional weight loss greater than 10% of body weight) and AIDS-related cachexia impair quality of life and prognosis. Mother-to-child transmission during pregnancy, delivery, or breastfeeding — occurring in up to 45% without intervention — is virtually eliminated (below 1%) with maternal ART and neonatal prophylaxis. Modern ART-treated patients with suppressed viral load have near-normal life expectancy but require lifelong medication adherence.

Combined HIV prevention: Treatment as Prevention (TasP) — treating all HIV-positive people achieves U=U (Undetectable = Untransmittable); this is the single most powerful prevention strategy globally. Condoms: male and female condoms consistently reduce sexual transmission risk by 80-95%. PrEP: routine offer to all MSM, transgender women, sex workers, discordant couples, and others at substantial ongoing HIV risk. PEP: emergency treatment within 72 hours of potential exposure. Harm reduction for people who inject drugs: needle and syringe programmes (NSP), opioid substitution therapy (methadone, buprenorphine), and PrEP. Mother-to-child transmission prevention (PMTCT): ART throughout pregnancy and breastfeeding, intrapartum prophylaxis, and infant prophylaxis reduces vertical transmission to below 1%. Regular STI testing and treatment: STIs (particularly ulcerative STIs — syphilis, herpes) increase HIV acquisition risk 2-8 fold. Psychosocial support: stigma and discrimination remain major barriers to HIV testing and treatment uptake — community-based peer support and HIV-positive support networks improve engagement.

Get tested for HIV if: you have had unprotected sexual intercourse with a partner of unknown HIV status; you have had a previous STI diagnosis; you inject drugs and share equipment; you have received a blood transfusion in a country without universal blood screening; or if a sexual partner has been diagnosed with HIV. In the UK, routine opt-out HIV testing is offered in all emergency departments in high-prevalence areas, antenatal clinics, and sexual health services. Seek immediate review if you experience: symptoms of seroconversion illness (fever, rash, sore throat, swollen glands) within 4 weeks of a potential HIV exposure — test even within the window period; or if you need PEP, which must be started within 72 hours of exposure. Established HIV-positive patients should see their HIV clinic every 3-6 months for viral load and CD4 monitoring, adherence support, and screening for comorbidities.