HIV/AIDS

HIV/AIDS represents one of the most destructive and socially complex pandemics of the 20th and 21st centuries. Since the first clinical cases were identified in 1981, the Human Immunodeficiency Virus has infected an estimated 85 million people and killed approximately 42 million — a death toll that continues to grow, because HIV/AIDS remains an ongoing pandemic with no cure and no vaccine. As of 2024, roughly 39 million people are living with HIV worldwide.

The virus's origin lies in the zoonotic transmission of a closely related chimpanzee virus (SIVcpz) to humans in the Congo Basin of west-central Africa, most likely in the 1920s. Genetic phylogenetics traces the global pandemic strain back to Kinshasa (then Léopoldville) in the Democratic Republic of Congo, where early urban growth, increased sexual networks, and large-scale colonial medical campaigns using unsterilized needles may have enabled the virus to establish itself in the human population. It remained largely undetected for decades, spreading slowly across Africa and eventually reaching Haiti and the United States through migrant workers and blood transfusions in the 1970s.

HIV attacks CD4+ T cells, the white blood cells that coordinate the human immune response. As the virus progressively destroys the immune system over years or decades, the infected person becomes unable to fight off opportunistic infections — diseases like tuberculosis, Pneumocystis pneumonia, toxoplasmosis, and Kaposi's sarcoma that a healthy immune system would suppress easily. This advanced stage of HIV infection is called AIDS (Acquired Immunodeficiency Syndrome). Without treatment, the median time from HIV infection to AIDS is roughly 10 years; from AIDS to death, another 1–3 years.

The virus is transmitted through specific bodily fluids: blood, semen, vaginal fluids, rectal fluids, and breast milk. It cannot be transmitted through casual contact. In the early epidemic, four main transmission routes dominated in different populations: unprotected sexual intercourse, sharing of injection drug needles, blood transfusions from infected donors, and mother-to-child transmission during birth or breastfeeding. The geography of transmission varied enormously: in Sub-Saharan Africa, heterosexual transmission drove the epidemic and infected entire communities; in Western nations, the early epidemic was concentrated among men who have sex with men and intravenous drug users, a pattern that shaped — and distorted — early public health responses.

The epicenter of the global epidemic is Sub-Saharan Africa, which bears nearly 70% of global HIV infections. Countries in southern Africa have been hardest hit: at the epidemic's peak in the late 1990s and early 2000s, Botswana, Lesotho, Eswatini, and Zimbabwe had adult HIV prevalence rates of 20–38%. The AIDS epidemic in Africa dismantled social structures, orphaned millions of children, devastated healthcare systems, and reversed decades of life expectancy gains.

The transformation came with antiretroviral therapy (ART). Early antiretroviral drugs arrived in the late 1980s, but the pivotal breakthrough was Highly Active Antiretroviral Therapy (HAART) introduced in 1996. By combining three or more drugs from different classes, HAART could suppress viral replication to undetectable levels, preventing immune system damage and rendering the patient unable to transmit the virus. HIV became a manageable chronic condition. Today, people diagnosed with HIV who access treatment promptly have near-normal life expectancy. The challenge is access: in low-income countries, millions still lack consistent access to ART, with funding shortfalls, stigma, and weak health systems as persistent barriers. The pandemic will not end without solving the equity problem.