Human immunodeficiency virus, or HIV, is part of a family of viruses called retroviridae, that is, a retrovirus. These viruses are unique because they make use of an enzyme called reverse transcriptase (in concert with another, called integrase) to make DNA out of their own genetic code, RNA, allowing the virus to integrate its own genes into those of its host's cells. HIV, as a retrovirus, has a number of characteristics that are important to understand.
History
It is thought that, through zoonosis (the crossing of a pathogen from animals to humans), HIV crossed from primates to humans sometime in the early twentieth century. A paper by Michael Worobey, et. al., details that HIV was already diverse (having different strains) before it ever reached pandemic levels. Note that the small RNA genetic code of HIV and other viruses mutates quickly because virus reproduction has no self-correcting mechanisms and because it happens very rapidly.
Types
HIV is divided into two major types, HIV-1 and HIV-2. HIV-1 is the more widely spread and more virulent (more pathogenic, that is, capable of causing disease) than HIV-2, which is found mostly in West Africa, according to the CDC (Centers for Disease Control). The severity of the degree to which the immune system becomes compromised due to infection with HIV-2 seems to be less than that of the disease associated with HIV-1, and HIV-2 is also somewhat less infectious (able to be transmitted). In addition to the two major types, there are many strains of HIV, and, because HIV can mutate within one person's body and because of multiple infections, it is possible that one individual may be infected with several strains of the virus.
Features
HIV is a lentivirus, which means that it is a slow-acting virus, sometimes taking up to twenty years to cause symptoms, during which time the virus is considered to be latent. During infection, HIV binds as an antigen to T cells, part of the body's immune defense mechanism, and this causes the proliferation of antibodies, which attack the virus. The point at which there are a detectable level of HIV antibodies is called seroconversion, and at this point an infected person will test positive for HIV.
Significance
Retroviruses are set apart from other viruses because they employ reverse transcriptase to make DNA out of the virus' RNA; using integrase, another enzyme, this new viral DNA is then spliced into host cells. This effectively turns the host cell into a factory for the production of more virus particles.
Effects
Because T cells, used in the body's defense against HIV, are themselves the target of the virus, the body is increasingly unable to fight off both HIV and other infections. When the body's CD4 (a type of T cell) level drops below 200 cells per µL, the body will no longer be able to fight off infections using the immune system, and a syndrome called AIDS (acquired immune deficiency syndrome) is said to develop. AIDS is a collection of conditions, such as pneumocystis pneumonia (PCP), thrush, and Kaposi's sarcoma (a type of skin cancer), which are called opportunistic infections; these do not appear in persons with healthily functioning immune systems.
Tags: because they, genetic code, HIV-1 HIV-2, host cells, immune system, major types