Following fusion of the virus with the host cell, HIV enters the cell. The genetic material of the virus, which is RNA, is released and undergoes reverse transcription into DNA. An enzyme in HIV called reverse transcriptase is necessary to catalyze this conversion of viral RNA into DNA. Once the genetic material of HIV has been changed into DNA, this viral DNA enters the host cell nucleus where it can be integrated into the genetic material of the cell. The enzyme integrase catalyzes this process, once the viral DNA is integrated into the genetic material of the host; it is possible that HIV may persist in a latent state for many years.
Activation of the host cells results in the transcription of viral DNA into messenger RNA (mRNA), which is then translated into viral proteins. The new viral RNA forms the genetic material of the next generation of viruses. The viral RNA and viral proteins assemble at the cell membrane into a new virus. Amongst the viral proteins is HIV protease, which is required to process other HIV proteins into their functional forms. Following assembly at the cell surface, the virus then buds forth from the cell and is released to infect another cell.
Host range
The HIV virus mainly infects humans. There are two species of HIV that infect humans;
- HIV 1 it is the more virulent and easily transmitted and is the source of the majority of HIV infections throughout the world. HIV 1 has evolved from a simian immunodeficiency virus (SIV cpz) found in the chimpanzee subspecies.
- HIV 2 is largely confined to West Africa. HIV 2 crossed species from a different strain of SIV, found in sooty mangabey monkeys in guinea-Bissau.
Both species originated in west and central Africa, jumping from primates to humans in a process known as zoonosis.
Mode of transmission
HIV can be transmitted in several ways.
The sexual behaviours that can transmit HIV are;
- Vaginal sex- If a man with HIV has sexual intercourse without a condom, infected fluid can pass into the woman’s blood stream through a tiny cut or sore inside her body.
- Anal sex- If a couple have anal sex, the risk of infection is greater than with vaginal intercourse because the lining of the anus is more delicate.
- Oral sex- With an infected partner does carry some risk of infection though very rare. The virus could get into the blood if you have bleeding gums, tiny sores or ulcers in the mouth.
The body fluids containing HIV include;
- Blood transfusions- Some people have been infected through a transfusion of infected blood.
- Blood products- such as those used by people with haemophilia.
- Semen and possibly pre-seminal fluid
- Vaginal secretion
- Breast milk
Over ways that HIV can be transmitted;
- Injecting drugs- the virus can be passed by sharing needles, syringes, spoons, filters and water.
- Mother to child transmission- an infected pregnant woman can pass the virus to her unborn child either before or during birth.
- Infection in the health care setting- some health care workers have become infected with HIV by being stuck with needles containing HIV-infected blood.
- Tattoos/piercing- if the equipment is not sterile, having a tattoo/piercing done could carry a very small risk.
Clinical features
The most common clinical problems that HIV sufferers is;
- weight loss
- Fungal nail infections
- Oral ulcers
- Angular cheilitis (inflammation of the mouth)
- Herpes
- Respiratory tract infections
- Chronic diarrhoea
- Fever
- Thrush
- TB
- Pneumonia
- Acute renal failure
- Dementia
There are some clinical problems caused by opportunistic infections. These take advantage of the opportunity offered by a weakened immune system. The main opportunistic infections are;
- Protozoal diseases e.g. PCP (pneumonia) and microsporidiosis (an intestinal infection).
- Bacterial diseases e.g. Tuberculosis and septicaemia.
- Fungal diseases e.g. candidiasis (skin infection) and cryptococcosis (pulmonary infection).
- HIV associated malignancies e.g. Kaposi’s sarcoma (vascular cancer) and squamous cell carcinoma (cancer).
Symptoms
The first symptoms of HIV infection can resemble symptoms of common cold or flu viruses. The symptoms of early infection can also be similar to the symptoms of other sexually transmitted diseases and other infections such as ‘mono’ or hepatitis. Some people who contract HIV experience very strong symptoms, but others experience none at all. Those who do have symptoms generally experience;
Other common symptoms can include;
- Headaches
- Swollen lymph nodes
- Sore throat
These symptoms can occur within days or weeks of the initial exposure to the virus during a period called primary or acute HIV infection.
Antibiotic treatment
There are several different antibiotics available to HIV infected people. But before medication is prescribed two tests have to be carried out. These tests are;
- Viral load test- This test measures the amount of HIV in your blood.
- CD4 test-The CD4 test measures the number of T- helper cells in your blood. The more cells you have per cubic millimetre of blood, the stronger your immune system. Patients that have a CD4 count below 200 cells per millimetre of blood should start antiretroviral therapy.
The main type of treatment for HIV or AIDS is antiretroviral therapy (ATR). It is not a cure, but it can stop people from becoming ill for many years. The treatment consists of drugs that have to be taken every day for the rest of someone’s life. HIV is a virus and like other viruses, when it is in the cell in the body it produces new copies of itself. With these new copies, HIV can go and infect other previously healthy cells. Antiretroviral treatment consists of drugs which work against HIV infection itself, by slowing down the replication of HIV in the body. The drugs are often referred as;
- Antiretrovirals
- Anti-HIV
- HIV antiviral
For antiretroviral treatment to be effective for a long time, it has been found that you need to take more than one antiretroviral drug at a time. This is what is known as combination therapy. The term highly active antiretroviral therapy (HAART) is used to describe a combination of three or more anti-HIV drugs. When HIV replicates it often makes mistakes. This means that within any infected person there are many different strains of virus. Occasionally, a new strain is produced that happens to be resistant to the effects of ATR. If the person isn’t taking any other type of drug then the resistant strain is able to replicate quickly and the benefits of treatment are lost.
There are four main groups of anti-HIV drugs. They are;
- Nucleoside/nucleotide reverse transcriptase inhibitors- They work by making sure that during replication, the DNA copy is faulty so the process cannot continue.
- Non-nucleoside reverse transcriptors inhibitors- These also stop the HIV from replicating. They do it by inhibiting the action of the enzyme reverse transcriptase.
- Protease inhibitor- Almost every living cell contains some type of protease. In the final stages of HIV replication, the infected human cell produces long chains of viral proteins. These must be cut up into smaller pieces from which to construct the cores of mature virus particles. Protease inhibitors prevent a special type of HIV protease from carrying out this process and so prevent the production of mature infectious viral particles.
- Fusion or entry inhibitors- In order to enter a human cell, HIV must first attach itself to the cells surface and then fuse its envelope with the cell’s membrane. The attachment process typically involves the binding of an HIV surface protein (gp 120) with a human cell surface protein (CD4) and then fusion process involves a HIV surface protein (gp 41). Entry inhibitors interfere with these proteins.
So unlike the three other classes of drugs, entry inhibitors act against the HIV before it has enters the cell.
Diagram 1
www.petech.ac.za
Diagram 2
www.avert.org
Graphs made using data from www.avert.org
Bibliography
Books
A new introduction to human biology
The new book of knowledge
Leaflets
NHS HIV facts
Websites
www.hivinsite.ucsf.edu
www.avert.org
www.wikipedia.com