Final answer:
The HIV/AIDS epidemic is caused by the Human Immunodeficiency Virus (HIV), with HIV-1 being the most widespread variant. This retrovirus affects the immune system and is prevalent throughout the world, especially in sub-Saharan Africa.
Step-by-step explanation:
The HIV/AIDS epidemic in humans is caused by the Human Immunodeficiency Virus (HIV). HIV-1 is the variant that occurs worldwide, whereas HIV-2 is mainly found in West Africa. This retrovirus attacks the immune system, particularly helper T cells (CD4+ T cells), which are crucial for the body's immune response. Since it was first identified in 1981, it has become a pandemic, especially affecting sub-Saharan Africa.
HIV is transmitted through sexual contact, contaminated bodily fluids, and from mother to fetus. While there is no cure for HIV, medications can slow its progression. Unfortunately, regions with the highest prevalence, like sub-Saharan Africa, often lack sufficient access to these lifesaving drugs and prevention strategies, exacerbating the epidemic's impact.