HIV/AIDS: definition prevention, treatment, diagnosis, causes
HIV (human immunodeficiency virus) infection can cause AIDS (acquired immunodeficiency syndrome).
HIV proliferates within the human immune system. The virus consists of an outer envelope with docking sites, an inner core containing the genetic information for replication of the virus, and enzymes that regulate this replication. HIV destroys certain white blood cells known as T helper cells or CD4 cells.
The human immune system generally manages to keep HIV in check for years. This means that although the virus is present in the body, the affected person has no symptoms and does not appear to be ill. At this stage the person is said to be HIV-infected, or HIV-positive.
Prevention is still the only effective means of protection against HIV infection. Awareness of the risk of infection and observance of protective measures are, therefore, of the utmost importance. Currently, prevention measures such as PrEP and PEP are available to suppport the standard recommended safe sex and safe injection practices.
Pre-exposure prophylaxis (or PrEP) for people at high risk for HIV allows to lower the chances of getting infected. PrEP prevents HIV from taking hold and proliferating. Daily PrEP reduces the risk of getting HIV from sex by more than 90%. Among people who inject drugs, it reduces the risk by more than 70%. The risk of getting HIV from sex can be further lower by combining PrEP with condoms and other prevention methods.
PEP, on the other hand, stands for post-exposure prophylaxis, and involves taking antiretroviral medicines (ART) after being potentially exposed to HIV to prevent becoming infected. PEP must be started within 72 hours after a recent possible exposure to HIV.
Both PrEP and PEP are highly effective, but the use of condoms and safe injection practices are still essential to prevent the infection.
Anti-HIV drugs inhibit proliferation of the virus by interfering with various phases of its life cycle. They are always used in combination therapy:
- Reverse transcriptase inhibitors (RT inhibitors) interfere with transcription of the genetic information of the virus from RNA into DNA. They inhibit a process that results in the genetic material of the virus being incorporated into the genetic material of the infected cell.
- Protease inhibitors deprive the virus of proteins that it needs to infect new cells. Although new viral particles continue to be formed, they are unable to infect new cells.
- Fusion inhibitors prevent HIV from entering, and thus infecting, cells. Uninfected cells are protected.
Combination therapy with at least two drugs often reduces viral replication to such an extent that the viral load falls below the detectable limit. Strict observance of the prescribed therapeutic regimen is very important for success. Rapid adaptation of viruses is leading to the development of resistance and cross-resistance to drugs. Thus, there is a need for continuing research and development of new therapies with novel mechanisms of action.
Shortly after being infected with HIV the affected person may develop an acute illness with flu-like symptoms. These symptoms subside after a few days, however, replication of the virus continues insidiously and unnoticed. Even though the infected person may feel well, the virus has commenced its drawn-out battle with the immune system and is spreading further and further throughout the body. Because of this, the disease often remains undiagnosed until it has reached an advanced stage.
Types of HIV tests:
- The HIV antibody test determines whether the virus has stimulated the body to produce immune substances, or antibodies. If HIV antibodies are found in the blood, the result is checked by means of a second blood test.
- The direct virus test, which is based on the polymerase chain reaction (PCR), allows to determine the amount of virus present in the blood, i.e. the ‘viral load’, helps to reliably monitor HIV infection and allows for rational use of available therapies.
- Resistance tests determine which medicines are effective against the virus – an essential condition for effective treatment.
HIV is transmitted via body fluids that contain a large amount of virus. These include blood, semen, vaginal fluid and breast milk.
Methods of transmission with high risk of infection:
- Unprotected sexual intercourse
- Drug consumption with used injecting equipment
- During pregnancy via the umbilical cord, during birth or during breastfeeding
- Administration of blood and blood products, frequent blood transfusions
Human immunodeficiency virus replicates mostly in T helper cells. It does this by reprogramming the metabolism of the infected cell in such a way that it replicates, whereas the infected cell perishes. As T helper cells play an important role in the immune response, the infected person’s immune system becomes progressively weaker. Eventually, the immune system's defence collapses, allowing relatively harmless pathogens to transform into life-threatening opportunistic infections, including:
- Fungal infections (e.g. candidiasis, Pneumocystis pneumonia)
- Viral infections (e.g. herpes, cytomegalovirus)
- Cancers (e.g. Kaposi’s sarcoma, lymphomas, cervical cancer)