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.

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).

HIV infection in humans is considered pandemic by the World Health Organization (WHO).

From its discovery in 1981 to 2006, AIDS killed more than 25 million people. A third of these deaths are occurring in Sub-Saharan Africa, retarding economic growth and increasing poverty. According to current estimates, HIV is set to infect 90 million people in Africa, resulting in a minimum estimate of 18 million orphans.

HIV infects primarily vital cells in the human immune system such as helper T cells (to be specific, CD4+ T cells.

HIV infection leads to low levels of CD4+ T 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.

Most untreated people infected with HIV-1 eventually develop AIDS. These individuals mostly die from opportunistic infections or malignancies associated with the progressive failure of the immune system.

HIV progresses to AIDS at a variable rate affected by viral, host, and environmental factors; most will progress to AIDS within 10 years of HIV infection: some will have progressed much sooner, and some will take much longer.Treatment with anti-retrovirals increases the life expectancy of people infected with HIV.

Three main transmission routes for HIV have been identified. HIV-2 is transmitted much less frequently by the mother-to-child and sexual route than HIV-1.

UNAIDS and the WHO estimate that AIDS has killed more than 25 million people since it was first recognized in 1981, making it one of the most destructive pandemics in recorded history. .

Sub-Saharan Africa remains by far the worst-affected region, with an estimated 21.6 to 27.4 million people currently living with HIV.

South & South East Asia are second-worst affected with 15% of the total. AIDS accounts for the deaths of 500,000 children in this region. South Africa has the largest number of HIV patients in the world followed by Nigeria.

Countries such as Uganda are attempting to curb the epidemic by offering VCT (voluntary counselling and testing), PMTCT (prevention of mother-to-child transmission) and ANC (ante-natal care) services, which include the distribution of antiretroviral therapy.

Classification

There are two species of HIV known to exist: HIV-1 and HIV-2. HIV-1 is the virus that was initially discovered. It is more virulent, more infective, and is the cause of the majority of HIV infections globally. The lower infectivity of HIV-2 relatively poor capacity for transmission, HIV-2 is largely confined to West Africa.
Comparison Of HIV Species
Species Virulence Infectivity Prevalence Inferred Origin
HIV - 1 High High Global Common Chimpanzee
HIV - 2 Lower Low West Africa Sooty Mangabey

Signs & Symptoms

Infection with HIV-1 is associated with a progressive decrease of the CD4+ T cell count and an increase in viral load. The stage of infection can be determined by measuring the patient's CD4+ T cell count, and the level of HIV in the blood.

HIV infection has basically four stages : 1) Incubation period, 2) Acute infection, 3) Latency stage and 4) AIDS.

The initial incubation period upon infection is asymptomatic and usually lasts between two and four weeks. The second stage, acute infection, lasts an average of 28 days and can include symptoms such as fever, lymphadenopathy (swollen lymph nodes), pharyngitis (sore throat), rash, myalgia (muscle pain), malaise, and mouth and esophageal sores.

The Latency stage, which occurs third, shows few or no symptoms and can last anywhere from two weeks to twenty years and beyond. AIDS, the fourth and final stage of HIV infection shows as symptoms of various opportunistic infections.

Main symptoms of acute HIV infection.

The initial infection with HIV generally occurs after transfer of body fluids from an infected person to an uninfected one. The first stage of infection, the primary, or acute infection, is a period of rapid viral replication that immediately follows the individual's exposure to HIV leading to an abundance of virus in the peripheral blood with levels of HIV commonly approaching several million viruses per mL.

This response is accompanied by a marked drop in the numbers of circulating CD4+ T cells. This acute viremia is associated in virtually all patients with the activation of CD8+ T cells, which kill HIV-infected cells.

The CD8+ T cell response is thought to be important in controlling virus levels, which peak and then decline, as the CD4+ T cell counts rebound. A good CD8+ T cell response has been linked to slower disease progression and a better prognosis, though it does not eliminate the virus.

During this period (usually 2–4 weeks post-exposure) most individuals (80 to 90%) develop an influenza, the most common symptoms of which may include fever, lymphadenopathy, pharyngitis, rash, myalgia, malaise, mouth and esophageal sores, and may also include, but less commonly, headache, nausea and vomiting, enlarged liver/spleen, weight loss, thrush, and neurological symptoms. Infected individuals may experience all, some, or none of these symptoms. The duration of symptoms varies, averaging 28 days and usually lasting at least a week.

Because of the nonspecific nature of these symptoms, they are often not recognized as signs of HIV infection. Even if patients go to their doctors or a hospital, they will often be misdiagnosed as having one of the more common infectious diseases with the same symptoms. As a consequence, these primary symptoms are not used to diagnose HIV infection, as they do not develop in all cases and because many are caused by other more common diseases. However, recognizing the syndrome can be important because the patient is much more infectious during this period.

Latency stage

A strong immune defense reduces the number of viral particles in the blood stream, marking the start of the infection's clinical latency stage. Clinical latency can vary between two weeks and 20 years. During this early phase of infection, HIV is active within lymphoid organs, where large amounts of virus become trapped in the follicular dendritic cells (FDC) network.

The surrounding tissues that are rich in CD4+ T cells may also become infected, and viral particles accumulate both in infected cells and as free virus. Individuals who are in this phase are still infectious. During this time, CD4+ CD45RO+ T cells carry most of the proviral load.

AIDS

When CD4+ T cell numbers decline below a critical level of 200 cells per µL, cell-mediated immunity is lost, and infections with a variety of opportunistic microbes appear.

The first symptoms often include moderate and unexplained weight loss, recurring respiratory tract infections (such as sinusitis, bronchitis, otitis media, pharyngitis), prostatitis, skin rashes, and oral ulcerations.

Common opportunistic infections and tumors, most of which are normally controlled by robust CD4+ T cell-mediated immunity then start to affect the patient. Typically, resistance is lost early on to oral Candida species and to Mycobacterium tuberculosis, which leads to an increased susceptibility to oral candidiasis (thrush) and tuberculosis.

Later, reactivation of latent herpes viruses may cause worsening recurrences of herpes simplex eruptions.

Pneumonia caused by the fungus Pneumocystis jirovecii is common and often fatal. In the final stages of AIDS, infection with cytomegalovirus (another herpes virus) or Mycobacterium avium complex is more prominent. Not all patients with AIDS get all these infections or tumors, and there are other tumors and infections that are less prominent but still significant.

The majority of HIV infections are acquired through unprotected sexual relations. Sexual transmission can occur when infected sexual secretions of one partner come into contact with the genital, oral, or rectal mucous membranes of another.

The correct and consistent use of latex condoms reduces the risk of sexual transmission of HIV by about 85%.

In general, if infected blood comes into contact with any open wound, HIV may be transmitted. This transmission route can account for infections in intravenous drug users.

Since transmission of HIV by blood became known medical personnel are required to protect themselves from contact with blood by the use of universal precautions. People who give and receive tattoos, piercings, and scarification procedures can also be at risk of infection.

HIV has been found at low concentrations in the saliva, tears and urine of infected individuals, but there are no recorded cases of infection by these secretions and the potential risk of transmission is negligible..It is not possible for mosquitoes to transmit HIV.

Mother-to-child

The transmission of the virus from the mother to the child can occur in utero (during pregnancy), intrapartum (at childbirth), or via breast feeding. In the absence of treatment, the transmission rate up to birth between the mother and child is around 25%.[31] However, where combination antiretroviral drug treatment and Cesarian section are available, this risk can be reduced to as low as one percent.

Postnatal mother-to-child transmission may be largely prevented by complete avoidance of breast feeding.

Diagnosis

Many HIV-positive people are unaware that they are infected with the virus.

HIV-1 testing consists of initial screening with an enzyme-linked immunosorbent assay (ELISA) to detect antibodies to HIV-1.

Specimens with a reactive ELISA result are retested. If retest is reactive, the specimen is reported as repeatedly reactive and undergoes confirmatory testing with a more specific supplemental test (e.g., Western blot. Specimens that are repeatedly reactive by ELISA and reactive by Western blot are considered HIV-positive and indicative of HIV infection.

Modern HIV testing is extremely accurate.

Treatment

There is currently no publicly available vaccine or cure for HIV or AIDS. However, a vaccine that is a combination of two previously unsuccessful vaccine candidates was reported in September 2009 to have resulted in a 30% reduction in infections in a trial conducted in Thailand. Additionally, a course of antiretroviral treatment administered immediately after exposure, referred to as post-exposure prophylaxis, is believed to reduce the risk of infection if begun as quickly as possible.

Current treatment for HIV infection consists of highly active antiretroviral therapy, or HAART. This has been highly beneficial to many HIV-infected individuals since its introduction in 1996, when the protease inhibitor-based HAART initially became available.

Current HAART options are combinations (or "cocktails") consisting of at least three drugs belonging to at least two types, or "classes," of antiretroviral agents.

In developed countries where HAART is available, doctors assess their patients thoroughly: measuring the viral load, how fast CD4 declines, and patient readiness. They then decide when to recommend starting treatment.

HAART neither cures the patient nor does it uniformly remove all symptoms; high levels of HIV-1, often HAART resistant, return if treatment is stopped. Moreover, it would take more than a lifetime for HIV infection to be cleared using HAART.

Despite this, many HIV-infected individuals have experienced remarkable improvements in their general health and quality of life.

The development of HAART as effective therapy for HIV infection has substantially reduced the death rate from this disease in those areas where these drugs are widely available.

Prognosis

Without treatment, the net median survival time after infection with HIV is estimated to be 9 to 11 years.

In areas where it is widely available, the development of HAART as effective therapy for HIV infection and AIDS reduced the death rate from this disease by 80%, and raised the life expectancy for a newly diagnosed HIV-infected person to 20–50 years.