Stages of HIV Infection

The Different Stages of HIV Infection

HIV infects cells in the immune system and the central nervous system. The main type of cell that HIV infects is the T helper lymphocyte. These cells play a crucial role in the immune system, by coordinating the actions of other immune system cells. A large reduction in the number of T helper cells seriously weakens the immune system.

HIV infects the T helper cell because it has the protein CD4 on its surface, which HIV uses to attach itself to the cell before gaining entry. This is why the T helper cell is sometimes referred to as a CD4+ lymphocyte. Once it has found its way into a cell, HIV produces new copies of itself, which can then go on to infect other cells.

Over time, HIV infection leads to a severe reduction in the number of T helper cells available to help fight disease. The process usually takes several years.

HIV infection can generally be broken down into four distinct stages: primary infection, clinically asymptomatic stage, symptomatic HIV infection, and progression from HIV to AIDS.

Stage 1: Primary HIV Infection

This stage of infection lasts for a few weeks and is often accompanied by a short flu-like illness. In up to about 20% of people the symptoms are serious enough to consult a doctor, but the diagnosis of HIV infection is frequently missed.

During this stage there is a large amount of HIV in the peripheral blood and the immune system begins to respond to the virus by producing HIV antibodies and cytotoxic lymphocytes. This process is known as seroconversion. If an HIV antibody test is done before seroconversion is complete then it may not be positive.

Stage 2: Clinically Asymptomatic Stage

This stage lasts for an average of ten years and, as its name suggests, is free from major symptoms, although there may be swollen glands. The level of HIV in the peripheral blood drops to very low levels but people remain infectious and HIV antibodies are detectable in the blood, so antibody tests will show a positive result.

Research has shown that HIV is not dormant during this stage, but is very active in the lymph nodes. A test is available to measure the small amount of HIV that escapes the lymph nodes. This test which measures HIV RNA (HIV genetic material) is referred to as the viral load test, and it has an important role in the treatment of HIV infection.

Stage 3: Symptomatic HIV Infection

Over time the immune system becomes severely damaged by HIV. This is thought to happen for three main reasons:

  • The lymph nodes and tissues become damaged or "burnt out" because of the years of activity;
  • HIV mutates and becomes more pathogenic, in other words stronger and more varied, leading to more T helper cell destruction;
  • The body fails to keep up with replacing the T helper cells that are lost.

As the immune system fails, so symptoms develop. Initially many of the symptoms are mild, but as the immune system deteriorates the symptoms worsen.

Where do opportunistic infections and cancers occur?

Symptomatic HIV infection is mainly caused by the emergence ofopportunistic infections and cancers that the immune system would normally prevent. These can occur in almost all the body systems, but common examples are featured in the table below.

As the table below indicates, symptomatic HIV infection is often characterised by multi-system disease. Treatment for the specific infection or cancer is often carried out, but the underlying cause is the action of HIV as it erodes the immune system. Unless HIV itself can be slowed down the symptoms of immune suppression will continue to worsen.

System Examples of Infection/Cancer
Respiratory system Pneumocystis Carinii Pneumonia (PCP) Tuberculosis (TB) Kaposi’s Sarcoma (KS)
Gastro-intestinal system Cryptosporidiosis Candida Cytomegolavirus (CMV) Isosporiasis Kaposi’s Sarcoma
Central/peripheral Nervous system HIV Cytomegolavirus Toxoplasmosis Cryptococcosis Non Hodgkin’s lymphoma Varicella Zoster Herpes simplex
Skin Herpes simplex Kaposi’s sarcoma Varicella Zoster

Stage 4: Progression from HIV to AIDS

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

At present in the Moldova AIDS diagnosis is confirmed if a person with HIV develops one or more of a specific number of severe opportunistic infections or cancers. In other countries, like for example the US, someone may also be diagnosed with AIDS if they have a very low count of T helper cells in their blood. It is possible for someone to be very ill with HIV but not have an AIDS diagnosis.

WHO clinical staging of HIV disease in adults and adolescents (2006 revision)

In resource-poor communities, medical facilities are sometimes poorly equipped, and it is not possible to use CD4 and viral load test results to determine the right time to begin treatment. The World Health Organization has therefore developed a staging system for HIV disease based on clinical symptoms.

Classification of HIV Stages in Adults and Adolescents

Quantity (%) of CD4 lymphocites per ml blood Clinical Stage
asymptomatic, acute (primary) or primary generalized lymphadenopaphy
Symptomatic non А non С
AIDS related diseases
1. ≥500 (≥29%) A1 В1 C1*
2. 200–499 (14–28%) A2 В2 C2*
3. <200 (<14%) = AIDS indicator A3 В3 C3*

Cаthegories А3, В3 and С1, С2 and С3 are determining AIDS cases and are registered as such

Note: This information is cross-posted and slightly adapted from in order to emphasize some aspects refering particulary to Moldova. For more details, visual adds, updated information and primary sources, please visit web page.