HIV Progression and Symptoms

After infection, the HI virus enters the blood and attacks the body's immune system, specifically the important T-helper cell which co-ordinates the immune system's response to infections. The HI virus gains entry to the T-helper cell by attaching itself to the CD4 protein on the surface of the cell. Once the HIV has gained entry, it takes over the cell and replicates, seeking new T-helper cells to infect. The infected cell dies after a couple of days.

The HIV replication cycle: The virus that causes AIDS is shown budding out of a human immune cell, which the virus infects and uses to replicate. Visit the National Institute for Allergy and Infectious Diseases to learn more.

 

The body's natural response to an infection is to fight infected cells and replace the cells that have been lost. This response encourages the virus to reproduce itself. This is a gradual process that eventually damages the body's immune system and leaves the body vulnerable to infections and other diseases. The time it takes to do this varies from person to person, but averages at about nine years.

The normal range for CD4+T cells in a healthy person is 800-1200 cells per cubic millilitre of blood. When an HIV infected person's CD4+ T cell count falls below 200, he or she becomes increasingly vulnerable to opportunistic infections. In a person with a healthy immune system these infections would not normally be life-threatening but to an HIV-infected person they could be fatal.

Without treatment, the viral load, which refers to the relative amount of free virus in the blood plasma, will increase to the point where the body can no longer fight it.

The course of an HIV infection. Graph taken from Wikipedia, originally published as Figure 1 in Pantaleo, G. et al (February 1993) New concepts in the immunopathogenesis of human immunodeficiency virus infection. New England Journal of Medicine, Vol. 328(5).

 

The graph above shows viral load (red) against CD4+T cell count (blue). Note the increase in viral load soon after infection. During this period, a potential partner is at greatest risk of contracting the virus.

As the graph also shows, the time it takes between contracting HIV (primary infection) and becoming ill (symptomatic) can be up to 8 years.This asymptomatic stage is also known as a latency period. In many cases, an infected person is unaware of their status during this time as they have not yet fallen ill which means they might unknowingly be putting their partners at risk. This is where the importance of frequent HIV testing and knowing your status becomes apparent - even when you are not showing any signs of illness.

Read more about the stages of HIV here: WHO case definitions of HIV for surveillance and revised clinical staging and immunological classification of HIV-related disease in adults and children. World Health Organization.