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Questions and Answers
What is the primary function of the Pol gene in HIV?
Which co-receptor is primarily involved in the entry of HIV into CD4 cells?
What is the result of the reverse transcriptase enzyme's lack of proofreading mechanism?
What is the role of the Env gene in HIV?
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What is the final step of HIV replication?
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What is the primary function of the Gag gene in HIV?
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What is the response of cytotoxic lymphocytes to HIV in early infection?
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What percentage of people experience asymptomatic primary infection from HIV?
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What is the term for the stage where HIV RNA copies increase?
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What is the classification of HIV based on?
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What is the term for the primary infection stage?
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What is the test used to detect the viral antigen rather than the antibody?
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What is the most useful indicator of current immune status?
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What is the term for the stage where there is a steep increase in HIV RNA copies, leading to opportunistic diseases and death?
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What is the number of symptoms of HIV category C?
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What is the term for the production of a neutralising antibody against gp120 in all patients?
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What is the main reason why the term STI is preferred over STD?
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What is the primary reason for the increase in STIs among males?
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Which of the following is NOT a predominant mode of STIs?
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What is a common risk factor for STIs?
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How many STIs are mentioned in the text?
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Study Notes
HIV Structure and Replication
- HIV is a lentivirus, a member of the retrovirus family.
- There are two types of HIV: HIV-1 (most virulent) and HIV-2 (almost entirely found in West Africa).
- HIV has three major structural genes: Gag, Pol, and Env.
- Gag encodes nuclear proteins, Pol encodes viral enzymes (reverse transcriptase, integrase, protease), and Env encodes envelope glycoproteins.
- Reverse transcriptase transcribes single-stranded RNA into double-stranded DNA, but with no proofreading mechanism, making replication highly error-prone due to mutations.
- The viral envelope is a lipid bilayer that expresses gp120 and gp41, which produce a complex to bind to CD4.
HIV Entry into CD4 Cells
- gp120 mediates target recognition, and gp41 mediates fusion.
- Co-receptors (CCR5 and CXCR4) are present on host cells and are required for viral entry.
HIV Replication Steps
- Complementary DNA (cDNA) strand is produced from viral RNA by reverse transcriptase.
- A second cDNA strand is synthesized.
- cDNA is transported to the cytoplasm.
- Integrase cleaves cDNA and inserts it into the host genome.
- Viral products are transcribed by the host cell.
- The products are cleaved into proteins by the HIV protease enzyme.
- The proteins assemble into new virus particles.
- The virus buds from the cell surface.
Immune Response to HIV
- The humoral immune response involves B cells producing a 'neutralizing antibody' against gp120, but this fails to clear the virus.
- The cytotoxic immune response involves cytotoxic lymphocytes controlling HIV replication in early infection, but this is eventually overcome by progressive damage to the immune system.
Primary Infection and Stages
- Primary infection from HIV occurs 2-6 weeks after infection, also known as seroconversion.
- 40% of people who experience primary infection are asymptomatic.
- Symptoms of primary infection include fever, sore throat, malaise, athralgia/myalgia, lymphadenopathy, oro-genital ulceration, rash, headache, diarrhea, and oral candida.
- The three stages that proceed primary infection are acute HIV syndrome, clinical latency, and symptoms of AIDS.
HIV Classification
- HIV is classified using CD4 cell count categories.
HIV Classification Categories
- Category A: acute HIV infection, asymptomatic HIV infection, and persistent generalized lymphadenopathy.
- Category B: symptoms include bacillary angiomatosis, candidiasis, cervical dysplasia, fever, diarrhea, herpes zoster, idiopathic thrombocytopenic purpura, and more.
- Category C: symptoms include candidiasis of bronchi, trachea or lungs, cervical cancer, coccidioidomycosis, cryptococcosis, and more.
HIV Diagnosis
- Five tests are used to diagnose HIV: HIV antibody test, HIV p24 antigen test, CD4 count, HIV load (viral load/HIV RNA), and nucleic acid testing.
What is an STI?
- A sexually transmitted infection (STI) is an infection spread by sexual contact.
Why is the term STI preferred over STD?
- STI is preferred because not all cases of sexually transmitted infections show symptoms, unlike diseases.
Predominant Modes of STIs
- Two of the most common STIs are:
- Chlamydia
- Gonorrhoea
Types of STIs
- There are several types of STIs, including:
- Chlamydia
- Genital warts
- Gonorrhoea
- Herpes
- HIV
- Syphilis
Trends in STI Prevalence
- The number of males with STIs has increased due to an increase in men who have sex with men (MSM).
Risk Factors for STIs
- Certain factors increase the risk of getting an STI, including:
- Young age (especially <25 years old)
- Unprotected sex
- Having multiple sex partners
- Previous history of STIs
- Having sex under the influence of drugs/alcohol
- Not using condoms
- Having a sexual partner with an STI
- Not getting regular STI testing
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Description
Learn about the basic structure and replication of Human Immunodeficiency Virus (HIV), including its genes and enzymes. Understand the roles of Gag, Pol, and Env genes in the HIV replication process.
