12.3 HIV and AIDS

HIV, a retrovirus that attacks the immune system, is a global health challenge. Its complex structure and lifecycle, involving unique enzymes and surface proteins, enable it to infect and replicate within host cells, particularly CD4+ T cells.

Transmission occurs through bodily fluids, with sexual contact being the primary route. The infection progresses through distinct stages, from acute to chronic, eventually leading to AIDS if left untreated. Diagnosis, treatment, and prevention strategies have evolved, significantly impacting the global pandemic.

HIV Structure, Life Cycle, and Transmission

Structure and lifecycle of HIV

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• HIV structure consists of enveloped retrovirus containing two copies of single-stranded RNA genome
• Viral enzymes include reverse transcriptase, integrase, and protease enabling viral replication and integration
• Surface glycoproteins gp120 and gp41 facilitate binding and fusion with host cells (CD4+ T cells)
• HIV lifecycle involves entry through binding to CD4 and co-receptors (CCR5 or CXCR4)
• Fusion and uncoating release viral contents into host cell cytoplasm
• Reverse transcription converts RNA to DNA, then integrates into host genome
• Transcription and translation produce viral proteins
• Assembly, budding, and maturation create new infectious virions

Transmission routes of HIV

• Sexual contact through unprotected vaginal, anal, or oral sex transmits virus via bodily fluids
• Blood-borne transmission occurs through sharing needles or syringes (intravenous drug use)
• Contaminated blood products can transmit HIV through transfusion (rare in developed countries)
• Mother-to-child transmission possible during pregnancy, childbirth, or breastfeeding
• Risk factors include multiple sexual partners, unprotected sex, and intravenous drug use
• Men who have sex with men (MSM) and sex workers face higher risk of infection
• Living in high-prevalence areas or having previous sexually transmitted infections increases risk

Stages of HIV infection

• Acute HIV infection characterized by high viral load and flu-like symptoms
• Window period for antibody detection lasts several weeks
• Chronic HIV infection (asymptomatic phase) establishes viral set point
• Gradual decline in CD4+ T cell count occurs over several years without treatment
• Symptomatic HIV infection begins when CD4+ T cell count falls below 500 cells/mm³
• Increased susceptibility to infections and constitutional symptoms (weight loss, fever) emerge
• AIDS defined by CD4+ T cell count below 200 cells/mm³
• Opportunistic infections (pneumocystis pneumonia) and AIDS-defining cancers (Kaposi's sarcoma) develop

Diagnosis and treatment of HIV/AIDS

• Diagnostic tests include antibody tests (ELISA, Western blot), antigen/antibody combination tests, and nucleic acid tests
• Monitoring tools track CD4+ T cell count, viral load, and drug resistance
• Antiretroviral therapy (ART) combines at least three drugs from different classes (NRTIs, NNRTIs, PIs, INSTIs, entry inhibitors)
• Pre-exposure prophylaxis (PrEP) and post-exposure prophylaxis (PEP) prevent HIV acquisition
• Treatment as prevention (TasP) reduces transmission risk in HIV-positive individuals
• ART aims to suppress viral replication, restore immune function, and improve quality of life

Global impact of HIV/AIDS pandemic

• Disproportionate burden affects low- and middle-income countries (sub-Saharan Africa)
• Economic consequences include reduced workforce productivity and increased healthcare costs
• Social stigma and discrimination persist, hindering prevention and treatment efforts
• Public health measures include education campaigns, condom distribution, and needle exchange programs
• HIV testing, counseling services, and prevention of mother-to-child transmission (PMTCT) programs implemented globally
• Global initiatives like UNAIDS 90-90-90 targets and WHO guidelines aim to end AIDS epidemic
• Challenges include limited access to testing and treatment in resource-poor settings
• Adherence to long-term therapy and development of drug resistance remain ongoing concerns
• Vaccine development efforts continue despite numerous setbacks