A virus that targets the immune system can leave the body defenseless. HIV, the human immunodeficiency virus, infects and destroys CD4 T-lymphocytes, progressively weakening cellular immunity if untreated.

Transmission occurs through blood, sexual fluids, and from mother to child. Acute infection may cause a flu-like illness; a long asymptomatic phase often follows while viral replication continues. Without treatment, most people eventually progress to AIDS. Modern antiretroviral therapy suppresses viral load to undetectable levels, preserves immune function, and prevents transmission.

Testing, early treatment, pre-exposure prophylaxis, and safe practices form the prevention toolkit. Stigma still impedes care in many places. With sustained therapy, people living with HIV can expect near-normal life expectancy.

• Virus that attacks CD4 immune cells
• Transmitted by blood, sex, and perinatal routes
• Controllable with lifelong antiretroviral therapy
• Undetectable viral load prevents sexual transmission