W
An involuntary loss of more than 10% of body weight (especially muscle mass), plus at least 30 days of either diarrhea or weakness and fever. HIV-associated wasting syndrome is an AIDS-defining condition.
See Related Term(s): AIDS-Defining Condition
A type of antibody test used to confirm a positive result on an HIV screening test. (The initial screening test is usually an enzyme-linked immunosorbent assay [ELISA] or, less often, a viral load test). The immune system responds to HIV infection by producing HIV antibodies. A Western blot can detect HIV antibodies in the blood, oral fluid, or urine.
See Related Term(s): Antibody, Enzyme-Linked Immunosorbent Assay, Viral Load Test
Also known as: Leukocyte
A type of cell found in blood and lymph. White blood cells are key components of the immune system and help fight infection and disease. Examples of white blood cells include lymphocytes, neutrophils, eosinophils, macrophages, and mast cells.
The naturally occurring, non-mutated strain of a virus. When exposed to antiretroviral (ARV) drugs, wild-type HIV can develop mutations that make the virus resistant to specific ARV drugs.
See Related Term(s): Drug Resistance
The time period from infection with HIV until the body produces enough HIV antibodies to be detected by an HIV antibody test. This generally takes 2 to 8 weeks, but in some people it can take up to 6 months. During the window period, a person can have a negative result on an HIV antibody test despite being infected with HIV.
See Related Term(s): Seroconversion
Women's Interagency HIV Study (WIHS) 
(En español)
Started in 1993, the Women’s Interagency HIV Study (WIHS) is an ongoing federally funded study on women who have HIV or who are at risk for HIV. Analysis of biological specimens and medical and behavioral data collected on WIHS participants has contributed to the understanding of HIV, AIDS, and the effects of antiretroviral therapy (ART) in women.
World Health Organization (WHO) (En español)
The agency of the United Nations that provides global leadership on health-related matters. Responsibilities of the World Health Organization (WHO) include shaping the global health research agenda, setting health standards, promoting evidence-based policy options, providing technical support to countries, and monitoring and assessing health trends.