HIV Human Immunodeficiency Virus Human immunodeficiency virus (HIV) is a lentivirus (a member of the retrovirus family) that causes acquired immunodeficiency syndrome (AIDS), a condition in humans in which the immune system begins to fail, leading to life-threatening opportunistic infections. Infection with HIV occurs by the transfer of blood, semen, vaginal fluid, pre-ejaculate , or breast milk . Within these bodily fluids, HIV is present as both free virus particles and virus within infected immune cells. The four major routes of transmission are unsafe sex, contaminated needles, breast milk, and transmission from an infected mother to her baby at birth ( vertical transmission ). Screening of blood products for HIV has largely eliminated transmission through blood transfusions or infected blood products in the developed world. HIV infects primarily vital cells in the human immune system such as helper T cells (to be specific, CD4+ T cells ), macrophages , and dendritic cells . HIV infection leads to low levels of CD4+ T cells through three main mechanisms: First, direct viral killing of infected cells; second, increased rates of apoptosis in infected cells; and third, killing of infected CD4+ T cells by CD8 cytotoxic lymphocytes that recognize infected cells. When CD4+ T cell numbers decline below a critical level, cell-mediated immunity is lost, and the body becomes progressively more susceptible to opportunistic infections.
Classification *There are two species of HIV known to exist: HIV-1 and HIV-2. *HIV-1 is the virus that was initially discovered and termed both LAV and HTLV-III. It is more virulent, more infective and is the cause of the majority of HIV infections globally. *The lower infectivity of HIV-2 compared to HIV-1 implies that fewer of those exposed to HIV-2 will be infected per exposure . Comparison of HIV species Species HIV-1 HIV-2 Virulence High Lower Infectivity High Low Prevalence Global West Africa Inferred origin Common Chimpanzee Sooty Mangabey
The human immunodeficiency virus (HIV) is a type of virus called a retrovirus , which infects humans when it comes in contact with tissues such as those that line the vagina, anal area, mouth, or eyes, or through a break in the skin.
HIV infection is generally a slowly progressive disease in which the virus is present throughout the body at all stages of the disease.
Three stages of HIV infection have been described:
1. The initial stage of infection (primary infection), which occurs within weeks of acquiring the virus, and often is characterized by a "flu-" or "mono-"like illness that generally resolves within weeks.
2. The stage of chronic asymptomatic infection (meaning a long duration of infection without symptoms) lasts an average of eight to 10 years.
3. The stage of symptomatic infection, in which the body's immune (or defense) system has been suppressed and complications have developed, is called the acquired immunodeficiency syndrome (AIDS). The symptoms are caused by the complications of AIDS, which include one or more unusual infections or cancers, severe loss of weight, and intellectual deterioration (called dementia).
When HIV grows (that is, by reproducing itself), it acquires the ability to change (mutate) its own structure. This mutation enables the virus to become resistant to previously effective drug therapy.
The goals of drug therapy are to prevent damage to the immune system by the HIV virus and to halt or delay the progress of the infection to symptomatic disease.
Therapy for HIV includes combinations of drugs that decrease the growth of the virus to such an extent that the treatment prevents or markedly delays the development of viral resistance to the drugs.
The best combination of drugs for HIV has not yet been defined, but one of the most important factors is that the combination be well tolerated so that it can be followed consistently without missing doses.