Human immunodeficiency virus (HIV) is a member of the genus Lentivirus, part of the family of Retroviridae. Lentiviruses have many common morphologies and biological properties. Many species are infected by lentiviruses, which are characteristically responsible for long-duration illnesses with a long incubation period. Lentiviruses are transmitted as single-stranded, positive-sense, enveloped RNA viruses. Upon entry of the target cell, the viral RNA genome is converted to double-stranded DNA by a virally encoded reverse transcriptase that is present in the virus particle. This viral DNA is then integrated into the cellular DNA by a virally encoded integrase, along with host cellular co-factors, so that the genome can be transcribed. After the virus has infected the cell, two pathways are possible: either the virus becomes latent and the infected cell continues to function, or the virus becomes active and replicates, and a large number of virus particles are liberated that can then infect other cells.
There are two strains of HIV known to exist: HIV-1 and HIV-2. HIV-1 is the virus that was initially discovered and termed LAV. It is more virulent, relatively easily transmitted, and is the cause of the majority of HIV infections globally. HIV-2 is less transmittable and is largely confined to West Africa.
Since the original description in 1981 of an unusual cluster of cases of Pneumocystis carinii pneumonia and Kaposi's sarcoma in previously healthy homosexual males, substantial advances in our understanding of the acquired immune deficiency syndrome (AIDS) have been achieved.In 1984, Institut Pasteur of France discovered what they called the HIV virus, but it wasn't until a year later a US scientist, Dr. Robert Gallo confirmed that HIV was the cause of AIDS.The development of a diagnostic serologic test for HIV-1 in 1985 have served as the basis for developing improvements in diagnosis.
In addition, therapy was dramatically altered with the introduction of antiretroviral drugs in 1987 and revolutionized by combination treatment, known as highly active antiretroviral therapy (HAART), in 1996. In the three years following the introduction of HAART, mortality, AIDS, AIDS-defining diagnoses, and hospitalizations all decreased 60 to 80 percent. The EuroSIDA study, comparing this early HAART period to pre-HAART and later HAART (1998 to 2002) treatment periods, found a sustained decrease in mortality and progression to AIDS with ongoing HAART . Despite the absence of a cure, the natural history of the disease was radically changed .
Stages of HIV infection
HIV-1 infection is divided into the following stages:
- Viral transmission
- Primary HIV infection (also called acute HIV infection or acute seroconversion syndrome)
- Clinical latent period with or without persistent generalized lymphadenopathy (PGL)
- Early symptomatic HIV infection (previously known as "AIDS-related complex" or ARC and more recently referred to as Class B according to the 1993 CDC classification)
- AIDS (AIDS indicator condition according to the 1987 CDC criteria and revised 1993 CDC criteria that include a CD4 cell count below 200/mm3 regardless of the presence or absence of symptoms)
- Advanced HIV infection characterized by a CD4 cell count below 50/mm3
- Sexual intercourse
- Sharing needles or syringes (primarily for drug injection)
- Transfusion of blood and blood products
- Perinatal transmission -babies born to HIV-infected women may become infected before or during birth or through breast-feeding after birth.
- In health care setting, one can be infected with HIV after being stuck with needles containing HIV-infected blood or, less frequently, after infected blood gets into a worker’s open cut or a mucous membrane (for example, the eyes or inside of the nose).
Risk factors for HIV transmission include
- Viral load
- Lack of circumcision
- Sexual risk
- Presence of ulcerative sexually transmitted diseases
- Lack of circumcision
- Host and genetic factors- similarity of HLA-class-I alleles between HIV discordant couples may affect the risk of transmission, by selecting for viral strains that are more likely to escape the immune containment of the seronegative partner