The natural history of an illness is the term to describe the pattern of a disease if left untreated.

It is very important to understand the natural history of HIV.

Natural history of HIV

The natural history of HIV infection has several different periods including: infection, seroconversion, primary infection, chronic infection and late-stage illness.

Infection

This is the point when the virus infects the first cells. It then takes several hours for these newly infected cells to be carried with the virus to the lymph nodes.

During the next few days or weeks the virus continues to multiply in the lymph nodes. Lymph nodes are packed with CD4 cells, which HIV uses to reproduce.

Seroconversion

After building up in the lymph nodes, HIV burst out into the blood stream and infects other parts of the body. The amount of HIV throughout the body (viral load) reaches very high levels (often millions of copies/mL. As viral load increases, this high level of viral activity produces symptoms in up to 80% people. These symptoms include sweating, fevers, temperature, weakness and tiredness and, more rarely, mouth ulcers.

The body then produces an immune reaction to this new infection, and starts to produce antibodies to fight the virus. It usually takes 1-3 months after infection for antibodies to HIV to be strong enough to be detected on an HIV antigen test. Occasionally it can take longer.

Primary (HIV) infection – PHI

Also called early infection or acute infection. Primary infection describes the first six months after infection.

Chronic infection

Chronic infection describes HIV infection after the first six months. Chronic infection can last for many years. It can take from 2-10 years until the majority of people need treatment. With treatment, chronic infection can be life-long – ie 20, 30, or 40 or more years.

Late stage infection

Late stage infection is the most serious stage. This is usually in people who do not have access to treatment, who are only diagnosed very late, or whose treatment has stopped working. This used to be commonly called AIDS, but this term is now rarely used.

Effect of ARVs on viral dynamics of HIV infection

With ARV treatment, viral load should go down by at least 90% (1 log) after 1 month, and to below 50 copies/mL after 3-6 months.

• A few weeks after infection, your HIV viral load shoots up to very high levels – you are very infectious.
• Your body fights back – your viral load then drops to much lower levels in most people.
• Over the next 2-10 years your viral load increases slowly – your viral load is usually very high (around 50,000-200,000 copies/mL) by the time your CD4 count drops to 200 cells/mm³.
• In 2011, most guidelines recommend starting treatment before the CD4 count falls below 350 and some recommend starting at higher levels.
• ARV treatment stops HIV stops reproducing – this brings your viral load right down again.

If ARV treatment brings viral load down to less than 50 copies/mL, then treatment can last for many years.