Human Immunodeficiency Virus HIV Question And Answers

Human Immunodeficiency Virus (HIV)

 

Question 1. Write notes on laboratory diagnosis of HIV.
Or
Write down the laboratory diagnosis of HIV infection.
Or
Write a short note on lab diagnosis of HIV/AIDS.
Or
Write a short note on laboratory diagnosis of AIDS.
Answer:

Laboratory Diagnosis of HIV/AIDS

Read And Learn More: Microbiology Question And Answers

1. Immunological Tests

• Total leukocyte count and Total lymphocyte count show leucopenia and lymphocyte count decreases to 2000 mm3
• The count of CD4 + T cells is less than 200 mm3
• CD4 and CD8 ratios get reversed due to a decrease in the count of CD4 cells.
• There is an increase in IgG and IgA antibodies.

2. Specific Tests: Various specific tests used in laboratory diagnosis of HIV/AIDS infection are:

• Antigen detection test:
  • This is done by ELISA.
  • The antigen is detected during the window period and in the AIDS patient.
  • This test becomes negative when antibodies appear.
• Nucleic Acid Detection: This method is used in the diagnosis of HIV in all stages.
  • Target amplification test: In this, a PCR test is done for the detection of nucleic acid, and RT–PCR is done for quantification of viral load.
  • Signal amplification test: In this, a branched DNA test is done.
  • In situ hybridization: In this method, viral nucleic acid is detected inside the tissues by using probes.
• Virus isolation:
  • In this method, the lymphocytes of the patient are cultivated with uninfected lymphocytes in the presence of interleukin-2.
  • Conformity of the presence of the virus is by detection of p24 antigen and reverse transcriptase activity.
• Antibody detection:
  • The appearance of antibodies is 2 to 6 months prior to sexual exposure.
  • In the patient’s serum, IgG and IgM antibodies are seen.
  • For antibody detection, there are two types of tests, i.e. screening tests and confirmatory tests
•  Screening Tests:
  • ELISA
  • Rapid tests
    1. Dot blot assay
    2. Particle agglutination
    3. HIV spot and comb tests.
  • Simple tests.
• Supplemental Tests:
  •  Western blot test
  •  Indirect immunofluorescence test
  • Radio immunoprecipitation assay.

Screening tests:

• ELISA test: ELISA is the method most commonly used. It is a highly sensitive and specific test. ELISA test is an extremely good screening test and most laboratories use a commercial ELISA kit that contains both HIV-1 and HIV-2
• Rapid tests: These tests take less than 30 minutes and don’t require expensive equipment. The rapid tests include dot-blot assay particle agglutination, HIV spot, and Comb’s tests.
• Simple tests: They take 1–2 hours and do not require expensive equipment.

Supplemental tests:

• Western blot test: In this test, HIV proteins are separated by polyacrylamide gel electrophoresis. The separated proteins are blotted onto strips of nitrocellulose paper.
• These strips are reacted with test sera. Antibodies to HIV proteins, if present in test serum, combine with different fragments of HIV.
• The position of the color band on the strip indicates the fragment of antigen with which antibodies have reacted.
• The position of the band is indicative of the antigen with which it is reacted. Positive tests show the presence of at least two bands of antigen p24, gp41, and gp120/60.
• Indirect immunofluorescence test: HIV-infected cells are fixed onto glass slides and then reacted with serum followed by fluorescein-conjugated anti-human gamma globulin.
• In a positive test, apple-green fluorescence appears when examined under a fluorescent microscope.

Question 2. Write a short note on HIV.
Or
Draw a neat labeled diagram of HIV.
Or
Draw a schematic diagram of the human immunodeficiency virus (HIV).
Or
Draw and label a diagram of the human immunodeficiency virus.
Answer:

HIV means Human Immuno Deficiency Virus, which was discovered by Luc Montagnier.

• HIV leads to AIDS.
• HIV is a retrovirus and belongs to the genus Lentivirus

HIV occurs in two types, i.e. HIV-1 which is isolated from Europe, the USA, and Central Africa. Another is HIV-2 which is isolated from West Africa.

Morphology:

• It is a spherical-enveloped virus that is 90-120 nm in diameter.
• It has two identical copies of single-stranded positive sense
• RNA genome.
• The virus core is surrounded by a nucleocapsid composed of protein.
• The virus has a lipoprotein envelope and glycoproteins which are virus-coded.
• Major virus-coded envelope glycoproteins are projecting spikes on the surface and anchoring transmembrane pedicles.

Viral Genes and Antigens: HIV consists of three structural and five non-structural genes. Structural genes are gag, pol, and env, while non-structural genes are Tat, Rev, Nef, Vif, and Vpr which are present in HIV-1 and HIV-2. Other than this, HIV-1 contains Vpu and HIV-2 has Vpx.

1. Structural Genes: These genes are present in all retroviruses.

• Gag Gene:
  • Encodes for core and shell antigens of the virus.
  • Expressed as precursor protein p55.
  • The precursor protein is cleaved into three proteins, i.e. p15, p18, and p24.
• Env Gene:
  • Encode for envelope antigen, i.e. envelope glycoprotein (GP 160).
  • gp 160 is cleaved into gp120 which is a principle envelope spike antigen and gp 41 which is a transmembrane antigen.
• Pol Gene:
  • Encodes for reverse transcriptase.
  • Expressed as precursor protein p100.
  • Cleaved into three proteins, i.e. p31, p51, p64.

2. Non-structural Genes: Present only in HIV:

• Tat gene: Specific, a transactivating factor that enhances viral protein synthesis.
• Rev gene: Required for expression of the structural gene.
•  Nef gene: Regulates latent state of virus.
• Vif gene: Confer infectivity to virus
• Vpr gene: Stimulate promoter region of the virus
• Vpu and Vpx gene: Code for small virus protein. Enhance maturation as well as the release of progeny virus from cells.

Question 3. Write on the different clinical courses of HIV infection.
Answer:

The clinical course of HIV infection can present as follows:

1. Acute HIV infection:
   • It is characterized by acute onset of fever, malaise, sore throat, myalgia, arthralgia, skin rash, and lymphadenopathy.
   • Peripheral blood usually shows lymphocytosis.
   • Virus, viral nucleic acid, or viral p24 antigen may be detected during acute infection.
   • HIV antibodies are negative at the onset of the disease but become positive during its course.
2. Asymptomatic infection: In this course, all infected persons are usually well.
   • Patients show positive HIV antibody tests and are infectious.
3. Persistent generalized lymphadenopathy:
   • It is characterized by enlarged nodes (more than l cm) at two or more extragenital sites for at least 3 months.
   • Persistent generalized lymphadenopathy must be differentiated from other causes of lymphadenopathy, such as lymphomas.
4. Symptomatic HIV infection:
   • When the CD4+ T lymphocyte count falls below 400 per mm3, the patient may develop symptoms like fever, diarrhea, weight loss, night sweats, and opportunistic infections.
   • During this phase, some patients develop an illness which is known as an AIDS-related complex or condition.
   • When CD4+ cells fall below 200 per mm3, the titer of the virus increases markedly and there is the irreversible breakdown of immune defense mechanisms, which is defined as AIDS.
   • Most of the patients with HIV disease die of infections other than HIV, for example, Opportunistic infections and malignancies.
   • AIDS is the end stage of HIV infection.
   • In addition to opportunistic infections, the patient may also develop primary CNS lymphoma and progressive multifocal leukoencephalopathy.
   • Dementia, severe encephalopathy, myelopathy, peripheral neuropathy, diminished concentration, and motor disturbances may develop in patients with HIV infection.

Question 4. Describe The Diagnosis Of HIV Infection
Answer:

Diagnosis of HIV Infection

• Diagnosis of HIV infection is based on the history of the patient and laboratory diagnosis.
• History of Patient History of a patient plays an important role in making the diagnosis of a patient.
• The patient should be asked briefly about the following:
• The brief sexual history of the patient should be asked. Ask about the sexual partners of the patient.
• If the patient has multiple sexual partners or if he/she a homosexual.
• Ask the patient about recent or past blood transfusions or about any surgical procedures that he had gone through.
• Ask the patient about the sharing of needles or if he is a drug addict.
• Ask about the profession of the patient, and if he/she is a healthcare worker.
• All the above points along with laboratory investigations help in making the diagnosis of HIV patients.

Question 5. Mention modes of infection of HIV.
Answer:

Following are the modes of infection of HIV:

• Sexual intercourse, i.e. anal or vaginal, or oral.
• Transfusion of blood and blood products, i.e. by blood transfusion
• Tissue and organ donations
• Injections and injuries: Use of unsterile syringes and needles, sharing contaminated syringes and needles by drug abusers, needlesticks, and other accidental injuries.
• Perinatally, i.e. virus it is transmitted from mother to baby at birth and after birth through feeding the breast milk