AIDS- Definition, HIV, Mechanism, Transmission, Stages, Diagnosis, Prevention  


  • AIDS (acquired immune deficiency syndrome) is a serious and potentially life-threatening condition caused by the human immunodeficiency virus (HIV). HIV attacks and weakens the body’s immune system, making it easier for infections and diseases to take hold. 
  • It is one of the infectious diseases with the highest mortality rates in the world, especially in Sub-Saharan Africa, where the illness has significantly lowered life expectancy and adversely affected health outcomes in recent years.
  • The prevalence of AIDS varies depending on the region, but it remains a major public health concern worldwide. According to the World Health Organization, as of 2018, there were an estimated 38 million people living with HIV/AIDS worldwide.
  • HIV is a virus that attacks and affects the immune system, increasing the probability and seriousness of other infections and disorders. Without treatment, the infection may proceed to a more severe stage known as AIDS.
  • AIDS is the final stage of HIV infection. It occurs when the body’s immune system is severely compromised as a result of the infection.

AIDS Associated Disease Categories:


  • Diarrhea
  • Wasting (extreme weight loss)
  • Abdominal pain
  • Infections of the mouth and esophagus


70% of AIDS patients develop serious respiratory problems.

  • Bronchitis
  • Pneumonia
  • Tuberculosis
  • Lung cancer
  • Sinusitis
  • Pneumonitis


Opportunistic diseases and tumors of central nervous system. Symptoms many include:

Headaches, peripheral nerve problems, and dementia complex (Memory loss, motor problems, difficulty concentration, and paralysis).

Skin Disorders

90% of AIDS patients develop skin or mucous membrane disorders.

  • Kaposi’s sarcoma
  • Herpes zoster (shingles)
  • Herpes simplex
  • Thrush
  • Invasive cervical carcinoma

Eye Infections

50-75% patients develop eye conditions.

  • CMV retinitis
  • Conjunctivitis
  • Dry eye syndrome

Human Immunodeficiency Virus (HIV):

  • Human immunodeficiency virus (HIV) is the virus that attacks the body’s immune system.
  • It is a member of the genus Lentivirus, part of the family retrovirus.
  •  HIV is similar in structure to other retroviruses. It is generally spherical and has a diameter of about 120 nm. It is composed of two strands of RNA, 15 types of viral proteins, and a few proteins from the host cell it infected, all surrounded by a lipid bilayer membrane.
  • The virus is made up of a capsid core that stores the genetic information and has been encased in a protein envelope. Numerous spikes of the glycoprotein are present throughout the protein membrane. Glycoprotein’s inner component, gp41, is joined to the protein’s outer portion, gp120. Other proteins, including several HLA antigens, are also present in the HIV envelope (Human Leucocyte Antigen). Two folded RNA helices can be found in the HIV genome. Reverse transcriptase, an enzyme, is needed for the conversion of RNA into DNA. A different enzyme known as integrase aids in the integration of the viral DNA into the host cell.
  • These components work together to enable the virus to infect immune system cells and push them to replicate the virus. Each molecule in the virus contributes to the process, from viral attachment to budding.
Structure of HIV Virus

Fig: Structure of HIV Virus

Mechanism of action:

  • HIV (human immunodeficiency virus) is a retrovirus that causes AIDS (acquired immunodeficiency syndrome) by attacking and weakening the body’s immune system.
  • The mechanism of action of HIV involves several steps. First, the virus attaches to and enters certain immune cells, such as CD4+ T-cells, macrophages, and dendritic cells. This is accomplished through the interaction of HIV’s surface proteins, such as gp120, with specific receptors on the surface of these cells, such as CD4 and chemokine receptors.
  • Once inside the cell, HIV uses its enzyme reverse transcriptase to convert its viral RNA into DNA. The viral DNA then integrates into the host cell’s genome, where it can remain dormant for extended periods of time.
  • When the host cell is activated, the viral DNA is transcribed into new copies of HIV RNA, which are then used to synthesize the viral proteins and enzymes needed for the replication of the virus. This process is aided by the host cell’s own protein synthesis machinery.
  • The newly formed HIV particles are assembled and released from the host cell, and the cycle begins again as the virus infects new cells. As the virus replicates and spreads, it gradually destroys the body’s immune cells, leading to a weakened immune system and the development of AIDS.
Mechanism of action of HIV Virus

Fig: Mechanism of action of HIV Virus

Clinical Stages of AIDS:

The clinical stages of AIDS, also known as the HIV disease stages, are the different stages a person with HIV goes through from the time of their infection with the virus to the development of AIDS (acquired immunodeficiency syndrome).

The clinical stages of AIDS are based on the level of CD4+ T-cell count in a person’s blood. CD4+ T-cells, also known as CD4 cells or T-helper cells, are a type of white blood cell that plays a key role in the body’s immune response. HIV attacks and destroys CD4 cells, which weakens a person’s immune system and makes them more susceptible to other infections and diseases.

There are three clinical stages of AIDS:

Acute HIV infection

This is the first stage of HIV infection, and it occurs within 2-4 weeks after the virus enters the body. During this stage, a person may experience flu-like symptoms such as fever, sore throat, body aches, and swollen lymph nodes. However, not everyone will have symptoms at this stage.

Clinical latency (also called chronic HIV infection)

This is the second stage of HIV infection, and it can last for many years. During this stage, the virus is still active but reproduces at very low levels, and a person may not have any symptoms or only mild symptoms.


This is the final stage of HIV infection, and it occurs when a person’s immune system is severely weakened and they develop certain opportunistic infections or cancers. At this stage, a person is said to have AIDS and will require medical treatment to prevent or treat these infections.

It is important to note that with proper medical care, people with HIV can live long and healthy lives and may never progress to the AIDS stage. Early diagnosis and treatment with antiretroviral therapy (ART) can help prevent the progression of HIV to AIDS and improve a person’s overall health.


AIDS is caused by the human immunodeficiency virus (HIV), which attacks and weakens the immune system. HIV is primarily transmitted through sexual contact with an infected person, but it can also be transmitted through blood, breast milk, and other bodily fluids.

Here are the main ways that HIV is transmitted:

Sexual contact

HIV is most commonly transmitted through sexual contact with an infected person. This includes vaginal, anal, and oral sex. HIV can be transmitted through any sexual activity that involves the exchange of bodily fluids, such as semen, vaginal fluids, or blood.

Sharing needles or other drug injection equipment: HIV can be transmitted through sharing needles, syringes, or other drug injection equipment with an infected person. This is because these items can be contaminated with small amounts of blood from an infected person, which can then be introduced into the body of the person who is sharing the equipment.

Mother-to-child transmission

HIV can be transmitted from a mother to her child during pregnancy, childbirth, or breastfeeding. This is called mother-to-child transmission.

Blood transfusions

In the past, HIV was sometimes transmitted through blood transfusions with contaminated blood. However, today all donated blood is carefully screened for HIV and other infectious diseases, so the risk of HIV transmission through blood transfusions is very low.

It is important to note that HIV cannot be transmitted through casual contact, such as shaking hands, hugging, or sharing food or drinks with an infected person.


  • The diagnosis of AIDS (acquired immunodeficiency syndrome) is typically based on a combination of a person’s symptoms, medical history, and laboratory test results.
  • To diagnose AIDS, a healthcare provider will first ask about a person’s medical history, including any symptoms they may be experiencing, as well as their sexual history and any potential exposure to HIV (the virus that causes AIDS). The provider may also perform a physical examination to look for signs of HIV infection or other illnesses.
  • The definitive diagnosis of AIDS is based on laboratory tests that measure the level of CD4+ T-cells in a person’s blood. CD4+ T-cells, also known as CD4 cells or T-helper cells, are a type of white blood cell that plays a key role in the body’s immune response. HIV attacks and destroys CD4 cells, which weakens a person’s immune system and makes them more susceptible to other infections and diseases.
  • A person is considered to have AIDS if their CD4+ T-cell count is below 200 cells/mm3, or if they have certain opportunistic infections or cancers that are indicative of a severely weakened immune system. These infections and cancers are known as AIDS-defining conditions.
  • In addition to the CD4+ T-cell count, a healthcare provider may also order other laboratory tests to confirm the diagnosis of AIDS and assess a person’s overall health. These tests may include a viral load test to measure the amount of HIV in the blood, as well as tests to diagnose any other infections or illnesses a person may have.


  • The treatment of HIV (human immunodeficiency virus) infection involves the use of antiretroviral therapy (ART), which is a combination of medications that inhibit the growth and replication of the virus. ART is highly effective at suppressing the virus and can prevent the development of AIDS (acquired immunodeficiency syndrome), but it does not cure HIV infection.
  • ART typically consists of a combination of at least three different medications from at least two different classes of HIV drugs. These medications work in different ways to inhibit the virus, and using a combination of drugs reduces the risk of the virus developing resistance to treatment.
  • The specific medications and drug regimen used in the treatment of HIV infection will depend on a person’s individual circumstances, such as the stage of their infection and any other medical conditions they may have. A healthcare provider will work with the person to determine the best treatment plan for their needs.
  • A person with HIV may also require other medications in addition to ART to treat or prevent opportunistic infections, which are diseases that happen more frequently or are more severe in individuals with weakened immune systems.
  • It is important for a person with HIV to take their ART medications exactly as prescribed and to continue taking them even if they are feeling well. This will help suppress the virus and prevent the development of resistance to treatment. Regular medical follow-up is also essential to monitor the effectiveness of the treatment and to make any necessary adjustments.

Basics of HIV Prevention:

There are several effective strategies for preventing the transmission of HIV (human immunodeficiency virus), the virus that causes AIDS (acquired immunodeficiency syndrome).

  • One of the most effective ways to prevent HIV transmission is to use condoms consistently and correctly during sexual activity. Condoms provide a barrier that can prevent the exchange of bodily fluids that can transmit HIV, and they are highly effective at preventing the transmission of the virus when used consistently and correctly.
  • Another important strategy for preventing HIV transmission is to avoid sharing needles or other drug injection equipment. HIV can be transmitted through contaminated needles and other equipment, so it is important for people who inject drugs to use clean needles and equipment every time. Needle and syringe exchange programs and other harm reduction services can help reduce the risk of HIV transmission among people who inject drugs.
  • Another way to prevent HIV transmission is to get tested for the virus and, if necessary, start antiretroviral therapy (ART) as soon as possible. ART is a combination of medications that can suppress the virus and prevent the development of AIDS, but it is most effective when started early in the course of infection. Regular testing can help identify HIV infection early, so treatment can be started promptly.
  • It is also important to practice safer sex and avoid high-risk behaviors, such as having sex without a condom or having sex with multiple partners. And, for people who are pregnant, it is important to get tested for HIV and receive appropriate medical care to prevent mother-to-child transmission of the virus.
  • Overall, a combination of these strategies can help reduce the risk of HIV transmission and prevent the spread of the virus.


  • Fanales-Belasio E, Raimondo M, Suligoi B, Buttò S. HIV virology and pathogenetic mechanisms of infection: a brief overview. Ann Ist Super Sanita. 2010;46(1):5-14. doi: 10.4415/ANN_10_01_02. PMID: 20348614.
  • Turner BG, Summers MF. Structural biology of HIV. J Mol Biol. 1999 Jan 8;285(1):1-32. doi: 10.1006/jmbi.1998.2354. PMID: 9878383.
  • Detres LL. Al dia en patogenesis del VIH [Update on HIV pathogenesis]. Sidahora. 1995 Apr-May:13-4. Spanish. PMID: 11363197.
  • Volmink J, Marais B. HIV: mother-to-child transmission. BMJ Clin Evid. 2008 Feb 5;2008:0909. PMID: 19450331; PMCID: PMC2907958.
  • Richman DD. Introduction: challenges to finding a cure for HIV infection. Curr Opin HIV AIDS. 2011 Jan;6(1):1-3. doi: 10.1097/COH.0b013e328340ffa6. PMID: 21242886; PMCID: PMC3077900.
  • Moir S, Chun TW, Fauci AS. Pathogenic mechanisms of HIV disease. Annu Rev Pathol. 2011;6:223-48. doi: 10.1146/annurev-pathol-011110-130254. PMID: 21034222.
  • Sued O, Figueroa MI, Cahn P. Clinical challenges in HIV/AIDS: Hints for advancing prevention and patient management strategies. Adv Drug Deliv Rev. 2016 Aug 1;103:5-19. doi: 10.1016/j.addr.2016.04.016. Epub 2016 Apr 23. PMID: 27117711.
  • Billard L, Zhao Z. A review and synthesis of the HIV/AIDS epidemic as a multi-stage process. Math Biosci. 1993 Sep-Oct;117(1-2):19-33. doi: 10.1016/0025-5564(93)90015-3. PMID: 8400574.

Leave a Comment

Your email address will not be published. Required fields are marked *