HIV/AIDS

HIV/AIDS

  • Structure of HIV: HIV is a retrovirus containing two copies of single-stranded RNA. It has a protein coat (capsid) and an outer envelope with glycoproteins embedded in a lipid bilayer. [1]

  • Three main structural genes of HIV:

  • gag: encodes for the structural proteins of the virus, including the capsid (p24), matrix, and nucleocapsid proteins.

  • pol: encodes for the viral enzymes, including reverse transcriptase, integrase, and protease.

  • env: encodes for the envelope glycoproteins gp120 and gp41. These proteins are responsible for binding to the host cell and mediating fusion.

  • Replication of HIV:

  1. Attachment: HIV attaches to the host cell, primarily the CD4+ T helper (Th) cells. This attachment requires a coreceptor. [1]

  2. Fusion and uncoating: The virus fuses with the host cell membrane and releases its contents into the cytoplasm. [1]

  3. Reverse transcription: The viral enzyme reverse transcriptase converts the viral RNA into complementary DNA (cDNA). [1, 2]

  4. Integration: The viral cDNA integrates into the host genome as a provirus. [2]

  5. Transcription and translation: The viral DNA is transcribed into viral RNA and translated into viral proteins. [2]

  6. Assembly: New viral particles are assembled. [2]

  7. Budding: Intact virions bud out of the host cell membrane. [2]

  • Modes of Transmission of HIV: HIV is transmitted through intimate contact involving the exchange of body fluids. [3]

  • Sexual contact: This is the most common mode of transmission, responsible for the majority of cases. [3]

  • Contact with blood or other body fluids: This includes transmission through:

  • Intravenous (IV) drug use, where needles are shared. [3]

  • Transfusions or other blood product recipients. [3]

  • Occupational injuries, such as needlesticks or mucous membrane exposure in healthcare workers. [3]

  • Perinatal transmission: Transmission from mother to child can occur before, during, or after birth (through breast milk). [1]

  • Clinical Course of HIV and Criteria for AIDS Diagnosis:

  • Primary infection (acute, early infection): This stage may be asymptomatic or present with flu-like symptoms that resolve on their own. There is a high level of viremia (virus in the blood) and a decrease in CD4 T-cell count. [4]

  • Clinical latency: During this stage, there is an absence of clinical symptoms. Viremia decreases, and CD4 T-cell count increases. [4]

  • AIDS (acquired immunodeficiency syndrome): Viremia resurges, and CD4 T-cell count drops drastically, leading to profound immunosuppression. This makes the individual susceptible to life-threatening opportunistic infections and malignancies. [4]

  • AIDS diagnosis criteria: According to the CDC guidelines, AIDS is diagnosed when the absolute CD4+ T lymphocyte count falls below 200 cells/mL (normal range: 500-1500 cells/mL). [5]

  • Screening and Confirmatory Tests for HIV Antibodies:

  • Previous algorithm:Screen for HIV-1/HIV-2 antibodies using ELISA or rapid EIA. [6]

  • Confirm positive test results by repeating ELISA, followed by Western blot. [6]

  • Current algorithm:Fourth-generation HIV-1/HIV-2 antibody/p24 antigen combination immunoassay: [6-8]

  1. Patient serum is incubated with a solid phase containing HIV-1 antigens, HIV-2 antigens, and antibody to HIV-1 p24. [6]

  2. HIV-1 or HIV-2 antibodies in the sample bind to their respective antigens, and HIV-1 p24 antigen binds to anti-p24 on the solid phase. [7]

  3. After washing, a labeled anti-p24 conjugate and labeled HIV-1/HIV-2 antigens are added. [7]

  4. After another incubation and wash, a trigger solution or substrate/stop solution is added, and relative light units or optical absorbance is measured. [8]

  • Confirm positive results with a rapid EIA. [8]

  • Reasons for False-Positive and False-Negative ELISA Results in HIV Testing: The sources provided do not contain information on reasons for false-positive and false-negative ELISA results in HIV testing.

  • Concept of "Core Window" and Expected Serologic Findings: The sources provided do not contain information that explains the concept of "core window" and expected serologic findings.

  • Standard Laboratory Testing Protocol to Confirm HIV-Positive Status:

  • If the initial HIV-ELISA is positive, the current standard protocol involves confirming the result with a rapid EIA. [8]

  • Reasons for Performing a p24 Antigen Test and Procedure:

  • The p24 antigen test is included in the fourth-generation combination immunoassay to detect HIV infection earlier than antibody tests alone. [6, 7]

  • The procedure involves incubating patient serum with a solid phase containing anti-p24 antibodies. If p24 antigen is present in the sample, it will bind to the antibodies, and a signal will be generated after the addition of labeled conjugates and substrate. [6-8]

  • Requirements to Release a Positive HIV Result: The sources provided do not explicitly state the requirements to release a positive HIV result.

  • Laboratory Testing to Monitor HIV/AIDS Patients Over Time:

  • CD4 T-cell count: This is the best indicator of immune function in HIV-infected individuals. It involves incubating peripheral blood with fluorescent-labeled anti-CD4 and analyzing the results using flow cytometry. [8]

  • In untreated patients, the CD4 T-cell number progressively declines, and the CD4 T:CD8 T-cell ratio is less than 1:1. [8]

  • A CD4 T-cell count below 200/mL indicates stage 3 infection (AIDS). [8]

  • A significant decline in CD4 T-cell count over time may indicate a need to modify CART or administer prophylactic therapy for certain infections. [9]

  • Quantitative viral load assays: These assays measure the amount of HIV RNA circulating in the patient's plasma using methods like qPCR and bDNA. [9]

  • HIV RNA is detectable about 11 days after infection. [9]

  • Successful CART therapy leads to a drop in viral load to an undetectable level. [9]

  • A significant increase in viral load indicates a need for drug resistance testing and potential modification of CART. [9]

  • Drug resistance testing: This testing is crucial for guiding treatment decisions and ensuring the effectiveness of ART. [10]

  • Genotype resistance assays: Performed in clinical labs, these assays amplify HIV reverse transcriptase and protease genes from RNA in patient plasma using RT-PCR. The amplified products are sequenced and analyzed for mutations that confer resistance to antiretroviral drugs. [10]

  • Phenotype resistance assays: Conducted by specialized reference laboratories, these assays determine the ability of HIV from clinical samples to grow in the presence of antiretroviral drugs, providing information about the virus's susceptibility to different medications. [10, 11]

  • Testing of infants younger than 18 months:Maternal antibodies in infant serum can complicate serologic test results. Therefore, molecular methods like qualitative HIV-1 DNA PCR using the infant's peripheral blood mononuclear cells are preferred for diagnosis. [11]

  • Serologic testing at 12 to 18 months of age may be used to confirm the diagnosis. [11]