The stages of HIV infection

The mechanism and stages of infection

HIV infects immune system cells and cells of the central nervous system. The main cell that HIV infects is called the 'T helper' lymphocytes. This type of T lymphocytes is crucial cells of our immune (defense) system for coordinating all the other immune cells, and any damage or loss of T helper cells seriously impairs the immune system.

HIV infects the T helper cell because it contains on its surface CD4 protein which is necessary for HIV to infect a cell. T helper cells are therefore also known as CD4 lymphocytes.

Once it enters the T-helper cell, HIV takes control of it and begins to replicate (reproduce), and infected T-helper cells die in a few days. New viruses then look for a new T-helper cell to infect and replicate the entire process while, on the other hand, immune system rapidly kills HIV and HIV-infected cells, and replaces the T-helper cells that are destroyed.

HIV progression can generally goes through four distinct phases:
1. primary infection
2. clinically asymptomatic stage
3. symptomatic HIV infection
4. Progression from HIV to AIDS.

PHASE 1: Primary HIV Infection

The initial phase of the infection may be completely absent in many people. In the case of about 20% of those infected, it occurs immediately after the transmission of the infection, lasts for several weeks and has symptoms similar to a flu, which is sometimes called a seroconversion illness. After that the immune system begins to respond to a large amount of HIV in the peripheral blood by producing antibodies to the virus and cytotoxic lymphocytes.

At this stage, when the test results for antibodies to HIV (ELISA test), may be falsely negative.

PHASE 2: Clinical asymptomatic phase

The duration of this phase is individual, although the average is about 10 years. As its name suggests, is has no symptoms, but sometimes swollen glands may be present.

The amount of virus in peripheral blood drops to a very low levels, but the HIV antibodies are detectable in the blood.

Researchs show that during this phase, the virus is extremely active in the lymph nodes. Large amounts of T-helper cells are infected and die, and large amounts of virus is produced.

It is a new kind of test that measures small amounts of HIV to flee from the lymph nodes. This test, which measures HIV RNA (genetic material) is called a test of the virulence of HIV (viral load test) and has an increasing role in the treatment of HIV infection.

PHASE 3: Symptomatic HIV Infection

Over time the immune system loses the struggle and it is no longer able to contain HIV, which occurs due to three main reasons:
• The lymph nodes and tissues become damaged or depleted due to years of activity;
• HIV mutates and becomes more pathogenic, in other words, it becomes stronger and more diverse, leading to increased destruction of T-helper lymphocytes;
• The body is no longer able to keep up with replacing the T-helper cells that are destroyed and their number is rapidly decreasing.

Immune system fails and there are first signs of illness. Initially, symptoms are mild, with a further deterioration of the immune system; symptoms can get worse and become more difficult.

Where is possible for opportunistic infections and cancers to occure?

Symptomatic HIV infection is characterized by the appearance of opportunistic infections and cancers that would normaly be prevented by a healthy immune system. These diseases can occur in almost entire body and the most common examples are shown in the table below.

As the table indicates, symptomatic HIV infection includes multi-system diseases. The resulting disease or cancers are treated, but the real underlying cause is the HIV, and he continues to weaken the immune system allowing new diseases to appear. If the virus does not slow down the symptoms of immune suppression will continue to deteriorate.

System
Examples of the infection / tumor

The respiratory system
Pneumocystis carinii pneumonia (PCP), tuberculosis (TB), Kaposi's sarcoma (KS)

Gastro-intestinal tract
Cryptosporidioza, Candida, Cytomegolavirus (CMV), Isosporiasis, Kaposi's Sarcoma

Central / peripheral nervous system
Cytomegolavirus, Toxoplasmoza, Cryptococcosa, Non-Hodgkin lymph, Varicella Zoster, Herpes simplex

Skin
Herpes simplex, Kaposi's sarcoma, Varicella Zoster

STAGE 4: Progression from HIV infection to AIDS

As the immune system becomes more and more damaged the illnesses become more severe leading eventually to the diagnosis of AIDS.

AIDS diagnosis is confirmed when a person develops one or more serious opportunistic infections or tumors.

People can become very sick from HIV and still not develop AIDS.