HIV stands for Human Immunodeficiency Virus. HIV attacks your immune system, a system of organs and cells throughout the body which usually fight off infection and keep you well. HIV affects the immune system by targeting and destroying cells which normally fight off infection. The main cells infected by HIV are called the CD4 (or T4) cells — a type of white blood cell.

If you have been told that you are HIV positive, this means that you have been infected with HIV, and your immune system has made antibodies in response to infection. Howvever, different from many other diseases, HIV antibodies do not protect from further infection nor do they kill the virus. Instead, HIV continues to reproduce itself within the CD4 cells, creating ‘viral copies’ which cause further damage to the immune system. The more HIV reproduces, the greater the number of new cells likely to become infected and destroyed by the virus. If your immune system is weakened, this is described as being ‘immunosuppressed’ or ‘immunocompromised’. This means that you are at risk of developing ‘opportunistic illnesses’ or other more serious diseases that are associated with AIDS. Opportunistic infections are a class of rare conditions that are not usually seen in healthy individuals but can occur in immunocompromised individuals. These are discussed in more detail below. AIDS stands for acquired immune deficiency syndrome – the most advanced stage of HIV disease.

HIV treatments are drugs which stop the virus from reproducing, and so dramatically inhibit its ability to infect and destroy new cells. Treatments will prevent ongoing immune system damage and allow the immune system to partially restore itself.

The following is a description of what is called the ‘natural history’ of HIV or what happens in HIV disease without treatment. It’s important to remember that antiviral treatment has significantly altered this natural history, often stalling disease progression before immune system damage can cause illness or AIDS, and improving health and survival — including for people who have previously had opportunistic infections.

The natural history below describes the stages of HIV disease. It is a common, but not universal description of HIV disease. People often think that without treatment, HIV leads inevitably to illness and AIDS. However a small but significant number of people, called “long-term non-progressors” or “elite controllers”, are able to live with HIV for a long time.

Stage 1 – primary infection

When people first become infected with HIV, they may experience a flu-like illness, sometimes accompanied by a rash, which is referred to as seroconversion illness. Not all people who have been exposed to HIV will experience seroconversion illness. Some people have no symptoms at all.  Also known as acute HIV infection, it is the time at which HIV tests begin to return a positive result rather than a negative result.

Stage 2 – asymptomatic infection

For a number of years following infection, many people with HIV will feel well and be symptom-free. Despite feeling well, the virus is usually starting to damage the immune system.

Stage 3 – symptomatic illness

The symptoms people might experience at this stage include diarrhoea, minor skin conditions, minor oral (mouth) conditions, lack of energy, night sweats, and/or persistently swollen glands lasting longer than two months.  For some people in this phase, an illness may be more severe than it would be in an unifected individual.  For example, shingles might involve more than one nerve and the rash be more extensive and more painful.

Stage 4 – advanced disease (previously known as AIDS)

At this stage, HIV will have done great damage to your body’s ability to cope with illness and infection. People at this stage experience severe symptoms, and are at risk of opportunistic illnesses.  AIDS defining events are not the only illnesses which occur in advanced immunosuppression; there are serious non-AIDS conditions which can threaten life. Thus the term AIDS is used less frequently these days.

Opportunistic illnesses are infections which most people have been exposed to at some point in their lives but which are suppressed by healthy immune systems. HIV can weaken the immune system to the point where these infections can emerge. Alternatively, some people with weakened immune systems may become sick if exposed to an opportunistic illness for the first time, whereas people with stronger immune systems would not.

Some opportunistic illnesses can cause serious illness (including some types of cancers) or can be fatal. There are effective treatments available for most opportunistic illnesses. You can reduce the risk of some opportunistic illnesses by taking treatments that may prevent the illness from occurring. This is called prophylaxis. In particular, if your CD4 count is under 250, you should talk to your doctor about whether you should be taking prophylaxis. For some people, treating HIV involves using both antiviral and prophylactic treatments.

HIV treatments have dramatically changed the experience of living with HIV. A person recently diagnosed who is in the early stages of HIV infection can anticipate a life expectancy similar to their HIV-negative peers. However, every person is different so your experience of living with HIV will be based on the interaction of factors including:

• how advanced your HIV infection is when you are diagnosed
• how well you look after yourself emotionally and physically
• decisions about HIV treatments
• how well treatments work for you
• factors based on your own physiology and genetics
• co-infection with other illnesses such as sexually transmissible infections and hepatitis