HIV

The human immunodeficiency virus, commonly called HIV, is a retrovirus that primarily infects vital components of the human immune system such as CD4+ T cells, macrophages and dendritic cells. It also directly and indirectly destroys CD4+ T cells. As CD4+ T cells are required for the proper functioning of the immune system, when enough CD4+ cells have been destroyed by HIV, the immune system barely works, leading to AIDS. HIV also directly attacks certain human organs, such as the kidneys, the heart and the brain leading to acute renal failure, cardiomyopathy, dementia and encephalopathy. Many of the problems faced by people infected with HIV results from the failure of the immune system to protect them from certain opportunistic infections and cancers.

The clinical course of HIV-1 infection

Infection with HIV-1 is associated with a progressive loss of CD4+ T-cells. This rate of loss can be measured and is used to determine the stage of infection. The loss of CD4+ T-cells is linked with an increase in viral load. The clinical course of HIV-infection generally includes three stages: primary infection, clinical latency and AIDS (Figure 1). HIV plasma levels during all stages of infection range from just 50 to 11 million virions per ml {{ref|Piatak}}.

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Primary Infection

Primary, or acute infection is a period of rapid viral replication that immediately follows the individuals exposure to HIV. During primary HIV infection, most individuals (80 to 90 %) develop an acute syndrome characterised by flu-like symptoms of fever, malaise, lymphadenopathy, pharyngitis, headache, myalgia, and sometimes a rash {{ref|Kahn}}. Within an average of three weeks after transmission of HIV-1, a broad HIV-1 specific immune response occurs that includes seroconversion. Because of the nonspecific nature of these illnesses, it is often not recognized as a sign 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. Since not all patients develop it, and since the same symptoms can be caused by many other common diseases, it cannot be used as an indicator of HIV infection. However, recognizing the syndrome is important because the patient is much more infectious during this period. Some of the symptoms during this early stage of HIV include: Persistent or recurring headaches and fever, diarrhea lasting for more than a week, rapid weight loss, colored growths on the skin, swollen lymph glands, and memory loss.

Related Topics:
Fever - Malaise - Lymphadenopathy - Pharyngitis - Headache - Myalgia - Seroconversion

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Clinical Latency

As a result of the strong immune defence, the number of viral particles in the blood stream declines and the patient enters clinical latency (Figure 1). Clinical latency is variable in length and can vary between two weeks and 20 years. During this phase HIV is active within lymphoid organs where large amounts of virus become trapped in the follicular dendritic cells (FDC) network early in HIV infection. The surrounding tissues that are rich in CD4+ T-cells also become infected, and viral particles accumulate both in infected cells and as free virus. Individuals who have entered into this phase are still infectious.

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The declaration of AIDS

AIDS is the most severe manifestation of infection with HIV. Acute HIV infection progresses over time to clinical latent HIV infection and then to early symptomatic HIV infection and later, to AIDS, which is identified on the basis of certain infections. In 1990, the World Health Organization (WHO) grouped these infections and conditions together by introduced a staging system for patients infected with HIV-1. This was updated in September 2005. Most of these conditions are opportunistic infections that can be easily treated in healthy people.

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• Stage I: HIV disease is asymptomatic and not categorized as AIDS
• Stage II: include minor mucocutaneous manifestations and recurrent upper respiratory tract infections
• Stage III: includes unexplained chronic diarrhea for longer than a month, severe bacterial infections and pulmonary tuberculosis or
• Stage IV includes toxoplasmosis of the brain, candidiasis of the esophagus, trachea, bronchi or lungs and Kaposi's sarcoma; these diseases are used as indicators of AIDS.

In the USA, the definition of AIDS is goverened by the Centers for Disease Control and Prevention (CDC). In 1993, the CDC expanded their definition of AIDS to include healthy HIV positive people with a CD4 positive T cell count of less than 200 per µl of blood. The majority of new AIDS cases in the United States are reported on the basis of a low T cell count in the presence of HIV infection.

Related Topics:
Centers for Disease Control and Prevention - AIDS - AIDS cases in the United States - T cell

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Many factors such as host susceptibility and immune function {{ref|Clerici}}{{ref|Morgan2002a}}{{ref|Tang}}, health care and co-infections {{ref|Gendelman}}{{ref|Bentwich}}{{ref|Morgan2002b}}, as well as factors relating to the viral strain {{ref|Quiñones-Mateu}}{{ref|Campbell2004}} may affect the rate of progression to AIDS. Thus, following infection with HIV-1, the rate of clinical disease progression varies enormously between individuals.

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