Human immunodeficiency virus (HIV) is the causative agent for AIDS. It is a retrovirus with RNA as a genetic material. There are two main types HIV-1 and HIV-2. HIV-1 is the most common and infectious agent that has caused to the worldwide epidemic and has been classified into three groups namely as groups M,N and O where group M is the most prevelant and divided into at least 16 subtypes. 
At the end of 2007, there were 33.2 million people worldwide estimated to be living with HIV and 2.1 million resulted in deaths where 330,000 of these were of children under 15.  World Health Organisation (WHO) stated that HIV continues to be a major global public health issue, having claimed more than 32 million lives by July 2019:
"In 2018, 770 000 people died from HIV-related causes globally. There were approximately 37.9 million people living with HIV at the end of 2018 with 1.7 million people becoming newly infected in 2018 globally. 62% of adults and 52% of children living with HIV were receiving lifelong antiretrovial therapy (ART) in 2018. Global ART coverage for pregnant and breastfeeding women living with HIV is high at 80%. The WHO African Region is the most affected region, with 25.7 million people living with HIV in 2018. The African region also accounts for almost two thirds of the global total of new HIV infections." 
Modes of Transmission
HIV is usually transmitted via exposure to the infected body fluids (blood, semen, breast milk,etc,) through contaminated needles and syringes, tainted transfusions, the sharing of unsterilized razors during cutting practices, sexual contact, or other mechanisms and from HIV positive mother to child during pregnancy ( in utero) , at birth or through breast-feeding.,
The diagnosis and monitoring of HIV infections have been mainly implemented through CD4 T cell enumeration, serological assays ( antibody detection,) antigen detection (p24antigen detection) and testing for viral nucleic acid. A major disadvantage of antibody detection tests is their lack of sensitivity and tendency to produce false negative results during the window period (the time between infection and antibody production). Moreover, the serological assays available for HIV antibody detection in adults can not be reliably applied for infants as it is complicated by the fact that maternal HIV antibody can persist for first 18 months. , 
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