HIV

HIV isn't a very [blank_start]tough[blank_end] virus and can't [blank_start]survive[blank_end] outside the body for any significant time. It can be passed on only in [blank_start]body fluids[blank_end], such as blood, vaginal secretions and semen, but [blank_start]not[blank_end] saliva or urine. Infection can occur if you have [blank_start]unprotected sex[blank_end] with someone who is already infected, or if [blank_start]blood[blank_end] from such a person enters your bloodstream. For infection to occur, the body fluids have to be transferred [blank_start]directly[blank_end] into the body of the next host.

For the infection to occur, the body fluids have to be transferred directly into the body of the next host. This can occur in the following ways:

Reasons for lower estimates for HIV/ AIDS cases?

AIDS stands for [blank_start]acquired immune deficiency syndrome[blank_end]. It's caused by infection with the [blank_start]human immunodeficiency virus[blank_end] aka HIV. A syndrome is a collection of symptoms related to the same cause, in this case the action of HIV, which gradually destroys parts of the [blank_start]immune[blank_end] system. The symptoms of AIDS are those of [blank_start]opportunistic[blank_end] infections to which the patient becomes susceptible as their immune system is weakened.

HIV is a structurally [blank_start]complex[blank_end] virus, an example of an [blank_start]enveloped[blank_end] virus. The virus consist of [blank_start]RNA[blank_end] surrounded by a 20-sided (icosahedral) [blank_start]protein capsid[blank_end] (coat) enclosed in a layer of [blank_start]viral protein[blank_end]. The [blank_start]lipid envelope[blank_end] is formed from the [blank_start]host cell membrane[blank_end] as the new virus particles emerge from the cell cytoplasm. Sticking through the envelope are viral [blank_start]glycoprotein[blank_end] (gp) molecules.

Label the diagram:

[blank_start]HIV[blank_end] invades [blank_start]T helper cells[blank_end] within the immune system. Glycoprotein molecules, called [blank_start]gp120[blank_end], which are located on the virus surface, bind to the [blank_start]CD4[blank_end] receptors on the surface of the [blank_start]T helper cells[blank_end]. The envelope surrounding the virus fuses with the [blank_start]T helper cell[blank_end] membrane, enabling the virus [blank_start]RNA[blank_end] to enter the cell. [blank_start]Macrophages[blank_end] also have CD4 receptors, so the viruses can also infect them.

Label the diagram:

Once inside the host [blank_start]T helper cell[blank_end], the virus needs to make the host cell replicate new virus components. HIV genetic material is in the form of [blank_start]RNA[blank_end] not DNA. Therefore the first step is to reverse normal transcription and manufacture DNA from the RNA template. To do this, the virus uses an enzyme called [blank_start]reverse transcriptase[blank_end]. Viruses that contain RNA and use reverse transcriptase in this way are called [blank_start]retroviruses[blank_end]. Once the HIV DNA strand is produced, it is integrated into the host's DNA by another HIV enzyme, [blank_start]integrase[blank_end]. Once the HIV genome is integrated into the host cell's genome, it can be transcribed and translated to produce new virus [blank_start]proteins[blank_end].

The new HIV virus proteins produced, together with [blank_start]glycoproteins[blank_end] and nuclear material, are assembled into new viruses. The new viruses bud out of the T cell, taking some of the host cell [blank_start]surface membrane[blank_end] with them as their [blank_start]envelope[blank_end], and [blank_start]killing[blank_end] the cell as they leave. Infected T helper cells will also be destroyed by [blank_start]T killer cells[blank_end].

As the number of viruses increases, the number of host T helper cells increases.

What does a loss of T helper cells result in?

What factors does the course of HIV/ AIDS depend on?

AIDS has no cure

The Acute Phase:

The Chronic Phase:

In fit young people with a [blank_start]healthy[blank_end] lifestyle, the chronic phase can last for [blank_start]20[blank_end] years or more, especially if combined with [blank_start]drug[blank_end] treatment. Unfortunately, most HIV infection occurs in [blank_start]developing[blank_end] countries with little money available to provide drugs and amongst people who often don't have access to food or [blank_start]clean[blank_end] water. These people may develop AIDS within a [blank_start]few[blank_end] years of infection.

Eventually, the increased number of viruses in circulation ([blank_start]viral load[blank_end]) and a declining number of T helper cells indicates the onset of AIDS, the [blank_start]disease[blank_end] phase. The decreased number of T helper cells leaves the immune system vulnerable to other diseases. These are known as [blank_start]opportunistic infections[blank_end], which can rapidly be fatal. They often include [blank_start]pneumonia[blank_end] and TB. There can be significant [blank_start]weight loss[blank_end]. Patients can also develop [blank_start]dementia[blank_end] - memory and intellect loss. Also susceptible to tumours, such as [blank_start]Kaposi's sarcoma[blank_end]. This cancer is readily identified by purple/ black patches on the skin.

A normal T helper cell count is over 500 per mm cubed of blood. At what T helper cell count is there a high risk of opportunistic infections?

There is [blank_start]no[blank_end] treatment to get rid of HIV in someone who is infected with the virus because the virus is [blank_start]hidden[blank_end] inside T helper cells. But there are drugs available that [blank_start]reduce[blank_end] the production of more viruses. These are known as [blank_start]antiretroviral[blank_end] drugs.

Reverse transcriptase inhibitors:

Protease inhibitors:

Which other drugs have also been approved for use?

HIV can develop [blank_start]resistance[blank_end] to anti-HIV drugs and therefore these drugs are often given in [blank_start]combination[blank_end]. If the virus becomes resistant to one drug, it may still be susceptible to the other drugs being taken. Access to antiretrovirals is increasing across the world and with it comes a decline in the number of AIDS-related deaths.