The Different Stages of HIV Infection
HIV infects cells in the immune system and the central nervous system. The main cell HIV infects is called a T helper lymphocyte. The T helper cell is a crucial part of the immune system, and co-ordinates 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. The infected cells are often destroyed or stop working properly.
However, battling against HIV the immune system is rapidly killing virus particles and HIV-infected cells, and replacing the T helper cells that have been lost.
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. Large amounts of T helper cells are infected and die and a large amount of virus is produced.
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 loses the struggle to contain HIV. This is 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 of opportunistic 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 |
Find out more about opportunistic infections.
STAGE 4 : Progression from HIV to AIDS
As the immune system becomes more and more damaged the illnesses that present become more and more severe leading eventually to an AIDS diagnosis.
At present in the UK an AIDS diagnosis is confirmed if a person with HIV develops one or more of a specific number of severe opportunistic infections or cancers. However people can still be very ill with HIV but not have an AIDS diagnosis.
WHO disease staging system
In resource-poor countries and communities, sometimes medical facilities and testing is unavailable, and it isn't possible to decide the appropriate time to begin treatment on the basis of test results. The World Health Organization has developed a disease staging system for HIV infection which is not dependent on testing.
WHO disease staging system for HIV Infection and Disease in Adults and Adolescents
Clinical Stage I:
1. Asymptomatic
2. Generalized lymphadenopathy
Performance scale 1: asymptomatic, normal activity
Clinical Stage II:
3. Weight loss <10% of body weight
4. Minor mucocutaneous
manifestations (seborrheic dermatitis, prurigo, fungal nail infections,
recurrent oral ulcerations, angular cheilitis)
5. Herpes zoster
within the last five years
6. Recurrent upper respiratory tract
infections (i.e. bacterial sinusitis)
And/or performance scale 2: symptomatic, normal activity
Clinical Stage III:
7. Weight loss >10% of body weight
8. Unexplained chronic
diarrhoea, >1 month
9. Unexplained prolonged fever (intermittent
or constant), >1 month
10. Oral candidiasis (thrush)
11. Oral
hairy leucoplakia
12. Pulmonary tuberculosis
13. Severe bacterial
infections (i.e. pneumonia, pyomyositis)
And/or performance scale 3: bedridden <50% of the day during last month
Clinical Stage IV:
14. HIV wasting syndrome [i]
15. Pneumocystic carinii pneumonia
16. Toxoplasmosis of the brain
17. Cryptosporidiosis with diarrhoea
>1 month
18. Cryptococcosis, extrapulmonary
19. Cytomegalovirus
disease of an organ other than liver, spleen or lymph node (e.g.
retinitis)
20. Herpes simplex virus infection, mucocutaneous (>1
month) or visceral
21. Progressive multifocal leucoencephalopathy
22. Any disseminated endemic mycosis
23. Candidiasis of esophagus,
trachea, bronchi
24. Atypical mycobacteriosis, disseminated or
pulmonory
25. Non-typhoid Salmonella septicemia
26. Extrapulmonary
tuberculosis
27. Lymphoma
28. Kaposi's sarcoma
29. HIV
encephalopathy [ii]
And/or performance scale 4: bedridden >50% of the day during last month
Footnotes:
- HIV wasting syndrome: weight loss of >10% of body weight, plus either unexplained chronic diarrohea (>1 month) or chronic weakness and unexplained prolonged fever (>1 month).
- HIV encephalopathy: clinical findings of disabling cognitive and/or motor dysfunction interfering with activities of daily living, progressing over weeks to months, in the absence of a concurrent illness or condition, other than HIV infection, which could explain the findings.
More information
AVERT.org has more about HIV/AIDS treatment and care, and more about HIV testing.
Last updated August 17, 2005
