The Basics

The difference between HIV and AIDS  

Many people use the terms HIV and AIDS interchangeably, however they are not the same thing and it is important to understand the difference. HIV (Human Immunodeficiency Virus) is a virus that is transmitted from person to person by sexual activity, blood to blood contact or during childbirth. Once transmitted, HIV enters cells of the immune system (CD4 cells, also called T-cells) where it reproduces itself, killing CD4 cells in the process. The immune system usually protects us from disease and infection, but HIV weakens the immune system over many years meaning it cannot fight off other infections and diseases that a healthy immune system would normally be able to. A person infected with HIV is described as "HIV-positive," meaning they have tested "positive" to a specific HIV blood test. 

The term AIDS (Acquired Immune Deficiency Syndrome) refers to a more advanced stage of HIV infection. Someone is said to have AIDS if they are diagnosed with one or more of a specific list of infections/conditions as a direct result of a weakened immune system. The weaker the immune system the more a person is at risk of developing AIDS. In the past, before effective HIV treatment was available, most people living with HIV would go on to develop AIDS over many years. The situation is very different today. HIV medications, called antiretroviral medications (ARVs) or antiretroviral therapy (ART), significantly reduce the amount of HIV in the body, which in turn reduces damage to the immune system and prevents progression to AIDS. If someone already has AIDS, then starting on ARVs can allow the immune system to recover and restore health.

HIV transmission  

HIV is only spread via the following body fluids:

  • Blood
  • Semen
  • Vaginal fluids
  • Breast milk

The most common ways HIV is passed from one person to another are:

  • Penetrative sex without a condom
  • Reusing and sharing injecting drug equipment
  • Mother-to-child during pregnancy, birth, or through breastfeeding

HIV is NOT spread by:

  • Hugging
  • Kissing
  • Shaking hands
  • Sharing cutlery 
  • Contact with sweat or tears 

You can NOT contract HIV from:

  • Toilet seats
  • Swimming pools
  • Mosquitoes (or any other insects) 

What HIV does in your body  

When you are infected with HIV, there are multiple things happening to the cells in your immune system. When HIV enters your body, researchers believe that the virus attaches to a specific type of immune system cell called a dendritic cell. These cells are found in the mucus membranes that line the mouth, vagina, rectum, penis and the upper gastrointestinal tract. Scientists think that these dendritic cells move the virus from the site of the infection to your lymph nodes where HIV can infect other immune system cells. HIV can infect multiple cells in your body, including brain cells, but its main target is the CD4 lymphocyte, also called a CD4 cell or a T-cell. The steps of the life-cycle of HIV are important to know because the medications used to control HIV infection work by interrupting this replication cycle at different points. 

The process is broken down into the following steps:

  1. Attachment (or Binding) 
  2. Fusion
  3. Reverse Transcription
  4. Integration
  5. Transcription
  6. Assembly
  7. Budding

For a description of each step, click here. To watch a video explaining HIV replication, click here

Understanding CD4 count and viral load  

Monitoring your CD4 or T-cell count is critical in managing HIV and understanding how it is affecting you and your body. CD4 cells are a key part of your immune system. They are infected and destroyed by HIV. Sometimes, they can be depleted to such dangerous levels that they are no longer able to help your immune system work properly. If this happens, you could be at risk of developing AIDS or AIDS related illnesses.

A general guide to CD4 test results is:

  • 500 to 1,350 CD4 is the ‘normal’ range for adults
  • More than 500 CD4 indicates little or no immune system damage
  • Between 500 and 250 CD4 cells indicates some damage but it is unlikely you will be at risk of major opportunistic infections
  • Less than 250 CD4 indicates more serious immune system damage and suggests that you could be at risk of serious opportunistic illnesses

CD4 counts used to be the only way to understand how HIV was affecting your immune system. The CD4 count is a measure of the damage already done. The viral load is a measure of the risk of future damage. 'Viral load’ is the term used to describe the amount of the HIV virus present in your bloodstream. Knowing how much HIV is present is an important indicator of how much your immune system is at risk of damage, how well your treatments are working, or whether you should consider starting or changing treatments.

A viral load test is a simple blood test. The result of a test is given as the number of viral copies of HIV per millilitre of blood. A ‘copy’ is what HIV produces every time it grows inside a cell: the more copies, the more virus. The amount of virus in your blood may range from a very small number of copies in your blood (below 50 copies per millilitre of blood) to levels in the thousands, hundreds of thousands, or even millions. 

You viral load can be:

  • High (i.e. more than 100,000 copies per ml)
  • Moderate (i.e. 10,000 to 100,000 copies per ml) 
  • Low (i.e. less than 10,000 copies per ml)
  • Undetectable (i.e. less than 40 to 50 copies per ml) 

Undetectable viral load does not mean that you have 'cleared' the virus from your body. It means HIV is present, but in very small amounts (below the number that can be accurately measured by the tests that are available). At this level, the virus is replicating so slowly that little, if any, damage will be happening to your CD4 cells and immune system. Having an undetectable viral load also greatly lowers your chance of transmitting the virus to others.

On their own your viral load results are no cause for alarm. For example, a high viral load result does not mean you are going to be sick tomorrow. Or a low result after your results have been undetectable for some time does not mean you have suddenly “failed” in any way. Your viral load level is a rough guide to the likelihood of future damage to the immune system. So if your viral load is high it means that future damage is more likely. If it is low or undetectable it means future damage is less likely. In order to make decisions about treatments, the viral load has to be read together with the CD4 cell count.

For more information on viral load and CD4 count, click here

The stages of HIV infection and associated symptoms  

The three stages of HIV infection are illustrated below. People may progress through these stages at different rates, depending on a variety of factors. Within 2-4 weeks after HIV infection, many, but not all, people develop flu-like symptoms, often described as “the worst flu ever.” Symptoms can include fever, swollen glands, sore throat, rash, muscle and joint aches and pains, fatigue, and headache and can persist anywhere from a few days to several weeks. This is called “acute retroviral syndrome” (ARS) or “primary HIV infection,” and it’s the body’s natural response to the HIV infection. During this early period of infection, large amounts of virus are being produced in your body, meaning you are at particularly high risk of transmitting HIV to your sexual or drug using partners during this stage. 

After the acute stage of HIV infection, the disease moves into the “clinical latency” stage. “Latency” means a period where a virus is living or developing in a person without causing symptoms. During the clinical latency stage, people who are infected with HIV experience no HIV-related symptoms, or only mild ones. (This stage is sometimes called “asymptomatic HIV infection” or “chronic HIV infection.”) During the clinical latency stage, the HIV virus continues to reproduce at very low levels, although it is still active. If you take ART, you may live with clinical latency for several decades because treatment helps keep the virus in check. For people who are not on ART, the clinical latency stage lasts an average of 10 years, but some people may progress through this stage faster. It is important to remember that people in this symptom-free stage are still able to transmit HIV to others, even if they are on ART, although ART greatly reduces the risk of transmission.

AIDS is the stage of HIV infection that occurs when your immune system is badly damaged and you become vulnerable to infections and infection-related cancers called opportunistic infections. When the number of your CD4 cells falls below 200 cells per cubic millimeter of blood (200 cells/mm3), you are considered to have progressed to AIDS. You are also considered to have progressed to AIDS if you develop one or more opportunistic illnesses, regardless of your CD4 count. During this late stage of HIV infection, people with HIV may have the following symptoms:

  • Rapid weight loss
  • Recurring fever or profuse night sweats
  • Extreme and unexplained tiredness
  • Prolonged swelling of the lymph glands in the armpits, groin, or neck
  • Diarrhea that lasts for more than a week
  • Sores of the mouth, anus, or genitals
  • Pneumonia
  • Red, brown, pink, or purplish blotches on or under the skin or inside the mouth, nose, or eyelids
  • Memory loss, depression, and other neurologic disorders

Many of the severe symptoms and illnesses of HIV disease come from the opportunistic infections that occur because your body’s immune system has been damaged. Without treatment, people who progress to AIDS typically survive about 3 years. Once you have a dangerous opportunistic illness, life-expectancy without treatment falls to about 1 year. However, if you are taking ART and maintain a low viral load, then you may enjoy a near normal life span and will most likely never progress to AIDS.  

1) Acute Infection: During this time, large amounts of the virus are being produced in your body. This has been described as feeling like the 'worst flu ever'. 2) Clinical Latency: This stage of the disease, HIV reproduces at very low levels, although it is still active. During this period you may not have symptoms and this can last up to 8 years or longer. 3) AIDS: As your CD4 cells fall below 200 cells/mm3 you will be diagnosed as having AIDS. Without treatment people typically survive 3 years.