Human Immunodeficiency Virus 1 (HIV‑1) is an enveloped retrovirus and the principal etiologic agent of acquired immunodeficiency syndrome (AIDS). It belongs to the genus Lentivirus within the family Retroviridae. The virion measures about 80–100 nm and contains two copies of a positive‑sense single‑stranded RNA genome (~9.7 kb) enclosed in a conical capsid surrounded by a host‑derived lipid envelope studded with the surface glycoprotein gp120 and transmembrane gp41. HIV‑1 infects humans by targeting CD4‑positive T lymphocytes, macrophages and dendritic cells, leading to progressive immune deficiency if untreated.
Genomic organization, replication and diversity
The HIV‑1 genome encodes three primary polyproteins (Gag, Pol and Env) and several regulatory proteins (Tat, Rev, Nef, Vif, Vpr and Vpu). It possesses long terminal repeats at both ends that function in integration and transcription. After binding to the CD4 receptor and either CCR5 or CXCR4 co‑receptors, gp41 mediates fusion with the host cell membrane and release of the viral core. The reverse transcriptase synthesizes a complementary DNA copy of the RNA genome, which is then integrated into the host genome by integrase, establishing a provirus. Transcription of the provirus produces full‑length and spliced viral RNAs that are translated into proteins and packaged into new virions. HIV‑1 has a high mutation rate and undergoes frequent recombination, giving rise to numerous subtypes and circulating recombinant forms. Four major genetic groups (M, N, O and P) exist; group M is responsible for the global pandemic and comprises subtypes A–K as well as multiple recombinant forms. HIV‑1 is thought to have originated from cross‑species transmission of simian immunodeficiency virus from chimpanzees in Central Africa during the early twentieth century.
Global impact and key facts
HIV‑1 is globally distributed and remains one of the most important infectious diseases. According to UNAIDS, 40.8 million people worldwide were living with HIV in 2024 and 1.3 million people became newly infected that year. An estimated 630 000 people died from AIDS‑related illnesses in 2024. Transmission occurs primarily through sexual contact, blood exposure and vertical transfer during pregnancy, birth or breastfeeding. Without treatment, infection progresses through acute and chronic stages to AIDS, characterized by opportunistic infections and malignancies. Combination antiretroviral therapy suppresses viral replication, restores CD4 counts and transforms HIV infection into a manageable chronic condition. Preventive measures include condom use, harm‑reduction strategies, antiretroviral prophylaxis and voluntary testing. There is no curative therapy, but ongoing research focuses on vaccines, long‑acting antiretrovirals and gene‑editing strategies. HIV‑1 has reshaped public health and biomedical research. Its high variability and integration into the host genome necessitate lifelong therapy and pose challenges for vaccine design. Continued prevention, treatment and surveillance efforts are essential to control its spread and improve outcomes for people living with HIV. Related Terms: Human Immunodeficiency Virus 2, Human T‑Cell Leukemia Virus 1, Human T‑Cell Leukemia Virus 2, Human T‑Cell Leukemia Virus 3, Hepatitis D Virus