human immunodeficiency virus

The human immunodeficiency virus (HIV) is considered to be one of the most devastating infectious diseases to have emerged in the recent history.

• it is a chronic condition characterized by progressive immunodeficiency, a long clinical latency period and opportunistic infections (1)
• HIV is the cause of the acquired immune deficiency syndrome (AIDS)

HIV is a member of the lentivirus genus of the Orthoretrovirinae subfamily of the Retroviridae family of viruses (2)

• various different primates are naturally infected with more than 40 different lentiviruses, termed simian immunodeficiency viruses (SIVs)
• these viruses are largely nonpathogenic in their natural hosts
• cross-species transmissions of these SIVs from different primates resulted in the emergence of HIV (3)

HIV targets primarily CD4 positive cells (CD4+) and replicates rapidly within these cells throughout all stages of the infection

• normally a healthy human has a CD4+ count of 800 to 1200 cells per mm3  of blood
• HIV causes qualitative defects in function and progressive destruction of CD4 cell count which results in an immunological decline
• initially replacement of CD4 cells matches the rate of destruction, but in AIDS the gap between destruction and replacement widens and immunological failure occurs
• usually it takes a number of years for CD4 counts to reduce to levels which will compromise the immune system
• once the CD4+ count drops below 500 cells/mm3, minor infections including cold sores (herpes simplex), condyloma (warts) and fungal infections, thrush and vaginal candidiasis, may occur
• as the CD4+ count drops below 200 cells/mm3, patient becomes susceptible to the serious opportunistic infections and cancers characteristic of end stage HIV infection
• many of the characteristic consequences of AIDS are due to immunological failure (4,5).

An individual is said to have a HIV infection when he /she is recognized with HIV infection regardless of the clinical stage (which includes severe or stage 4 clinical disease also known as AIDS) and confirmed by laboratory criteria according to country definitions and requirements (3).

There are two distinct types of HIV:

• type 1 (HIV-1) - causes the majority of infections throughout the world
• type 2 (HIV-2) - seen mostly in West Africa, although individual cases have been reported in other parts of Africa, Europe, the Americas and Asia (India) (6).

Reference:

• (1) Sax Paul E, Cohen Calvin J, Kuritzkes Daniel R. HIV Essentials 2017. Jones & Bartlett Learning, 2017
• (2) World Health Organization (WHO) 2007. WHO case definitions of HIV for surveillance and revised clinical staging and immunological classification of HIV-related disease in adults and children  
• (3) Sharp PM, Hahn BH. Origins of HIV and the AIDS Pandemic. Cold Spring Harbor Perspectives in Medicine: 2011;1(1):a006841  
• (4) The Medical Foundation for AIDS & Sexual Health (MedFASH) 2005. HIV in primary care: an essential guide to HIV for GPs, practice nurses and other members of the primary healthcare team  
• (5) Klimas N, Koneru AO, Fletcher MA. Psychosom Med. Overview of HIV. 2008;70(5):523-30
• (6) Wilson E, Tanzosh T, Maldarelli F. HIV diagnosis and testing: what every healthcare professional can do (and why they should). Oral Dis. 2013;19(5):431-9.