Understanding HIV
What is HIV?
Human immunodeficiency virus or HIV is the virus that causes AIDS. HIV is a type of virus called a retrovirus.
What is a retrovirus?
The genes of most living things, including humans, are made of DNA. The DNA exists as a sequence of a code that can be read like a book. In the cell the code is read to make RNA which is then used as the code for the construction of proteins. In other words, the flow of genetic information in the cell is usually from DNA to RNA to protein.
The HIV virus, on the other hand, has its genetic material made from RNA. It has to insert its genetic code into that of the host cell in order to replicate. In order to achieve this it must first make a DNA copy so that it is compatible with the DNA of the host cell. DNA is then made using the code of the RNA. Since this is the opposite of the usual case the viruses that do this are called retroviruses.
What does an HIV virus look like?
This is an artist's drawing of a single HIV virus. As you can see, the virus has several layers, including an outer layer, an inner layer and a core shell. The outer layer is interrupted by glycoproteins (gp) which play an important role in the lifecycle of the virus, and are targeted by a new type of drugs called "entry inhibitors". Within the core shell lies the genetic material of the virus (RNA), as well as some of the enzymes the virus needs to replicate. This includes Reverse Transcriptase, an enzyme that catalyzes the production of DNA based on the RNA genetic code. NRTI and NNRTI drugs inhibit the Reverse Transcriptase enzyme and thus prevent the virus from replicating.
How does HIV live in humans?
HIV uses human cells, mainly white blood cells, as host cells to in which to replicate and thrive. The white blood cells that HIV uses as host cells are called CD4 T-lymphocytes, which are commonly called "CD4 cells" or "T-cells" for short. The numbers of these cells are what are referred to when someone discusses a "CD4 count," or a "T-cell count."
CD4 cells are used to fight infection and are a key element of the immune system. In the process of replication, HIV kills CD4 cells. By replicating and killing CD4 cells, HIV degrades the immune system and renders the patient more susceptible to infections that would otherwise be easily fought off. An adult with a healthy immune system generally has a CD4 cell count of from 600 to 12001
What is AIDS?
A person is diagnosed with AIDS, or acquired immunodeficiency syndrome, according to the U.S. Centers for Disease Control and Prevention (CDC), when they have tested positive for HIV and have one or both of the following conditions:
- A CD4 cell count (or T-cell count) of below 200 per cubic millimeter of blood
- One or more AIDS-related illnesses. These illnesses are sometimes referred to as opportunistic infections since they develop due to the weakened immune system.
What is the treatment for HIV or AIDS?
Every person is different and your doctor will design a specific medical plan for you. It is essential that you follow this plan exactly, taking your medications exactly as prescribed. Some of the medications you will receive are intended to fight opportunistic infections. Other medications target the HIV virus in order to block replication and protect the body's immune system. These drugs are called "antiretroviral drugs." Often several antiretroviral drugs are prescribed for maximum effect. This is sometimes called "cocktail" therapy or highly active antiretroviral therapy (HAART).
Why do treatments fail?
There have been huge advances in the treatment of HIV infection, with the primary weapon being the availability of up to 16 antiretroviral drugs in some countries. In many cases, HAART can reduce the level of virus replication often to a level where no virus can be detected in the blood by currently available tests. However, there are also many factors that can work against the effect of these antiretroviral drugs:
- The virus population in your body may contain some variants or species that are already resistant
- An antiretroviral drug may not have an optimal effect in your body due to high toxicity or side effects
- Your immune system may not work effectively
- Failure to take all your medicines, all the time, as instructed by your physician
- Newly resistant HIV may arise
What is HIV drug resistance?
The net result is that these factors can combine together to create a set of conditions where the virus continues to replicate, leading to drug resistance and treatment failure.
HIV mutates constantly. What does this mean? As HIV replicates, the enzyme called reverse transcriptase carries out the process of making DNA based on the code of the RNA. During the process, this enzyme makes many errors. These errors are called "mutations" and they cause unique, new strains of HIV to be created. Some mutations may allow the virus to replicate in the presence of an antiretroviral drug. These viruses are then said to be resistant to this drug.
With the continuation of this particular drug therapy, the rare resistant virus will continue to replicate and will eventually become dominant. At this point your virus has become resistant to one or more of the drugs in your drug therapy.