hiv

Chapter Overview

  • Topics Covered:

    • Clinical features of HIV and AIDS

    • Morphology of HIV

    • Opportunistic infections associated with HIV

    • Viral genes and antigens

    • Laboratory confirmation of HIV and AIDS

    • Antigenic variation and diversity of HIV

    • Strategies for HIV testing

    • Growth characteristics of the virus

    • Prognosis of HIV

    • Epidemiology and preventive strategies

Learning Objectives

  • Understand HIV structure, viral genes, and antigens.

  • Describe the pathogenesis of HIV.

  • Discuss laboratory diagnosis of AIDS and outline HIV testing strategies.

  • Explain the epidemiology and preventive strategies against HIV.

History of HIV and AIDS

  • Emerged in summer of 1981 with rare diseases like Kaposi's sarcoma and Pneumocystis carinii pneumonia reported among young adult homosexuals and drug users.

  • In 1983, LAV isolated from a West African patient by Luc Montagnier.

  • In 1984, Robert Gallo isolated a related retrovirus called HTLV-III.

  • The virus was officially named HIV in 1986.

Morphology of HIV

  • HIV is a spherical, enveloped RNA virus about 90-120 nm in size.

  • Nucleocapsid consists of an icosahedral shell and conical core with ribonucleoproteins.

  • The envelope contains glycoproteins (gp120 and gp41) crucial for infection.

Viral Genes and Antigens

  • HIV genome is made of two identical single-stranded, positive-sense RNA copies.

  • Key genes include:

    • Gag: codes for core proteins (e.g., p24).

    • Pol: codes for reverse transcriptase.

    • Env: codes for envelope glycoproteins (gp120 and gp41).

  • HIV-1 is the major type affecting global populations, with subtypes A to J identified; HIV-2 is less virulent and mostly found in West Africa.

Antigenic Variation and Diversity of HIV

  • HIV exhibits high mutation rates, resulting in antigenic variation.

  • Variants of HIV emerge, complicating immune response and treatment.

  • Two major strains arise from differences in tropism (CD4 receptor and co-receptor use).

Growth Characteristics

  • Observed differences in growth characteristics among HIV isolates:

    • Strains from asymptomatic patients often grow slowly.

    • Strains from symptomatic patients typically exhibit faster growth rates.

  • HIV is thermolabile, inactivated at 60°C in 10 minutes.

Epidemiology of HIV

  • Major transmission routes include:

    • Sexual contact with infected individuals.

    • Injection drug use via contaminated needles.

  • HIV can also be spread through blood transfusions and from mother to child.

  • Transmission variables impact rate and efficiency dependent on the context (geography, social behavior).

Pathogenesis of HIV

  • HIV infects CD4+ T lymphocytes, leading to impaired immune function.

  • The clinical progression of HIV leads to AIDS:

    • Acute HIV infection occurs 3-6 weeks post-exposure with flu-like symptoms.

    • Asymptomatic phase (clinical latency) may last years.

    • AIDS is characterized by opportunistic infections due to immune suppression.

Opportunistic Infections in AIDS

  • Opportunistic infections are a hallmark of AIDS, including:

    • Fungal infections (e.g., pneumocystis pneumonia).

    • Bacterial infections (e.g., tuberculosis).

    • Viral infections (e.g., CMV, herpes).

  • Patients may present with symptoms such as chronic cough, fever, and weight loss.

Laboratory Diagnosis of HIV and AIDS

  • Initial diagnosis relies on detecting antibodies to HIV using ELISA, followed by confirmatory tests (Western Blot).

  • Antigen tests (p24) can detect infection earlier.

  • PCR tests identify HIV RNA/DNA for diagnosis and viral load monitoring.

Strategies for HIV Testing

  • Testing strategies include:

    • Pre- and post-test counseling.

    • Mandatory screening for blood products.

    • Anonymous testing programs for at-risk populations.

Prognosis of HIV Infection

  • Prognosis depends on factors such as viral load, CD4 counts, and treatment adherence.

  • Early intervention can enhance quality of life and prolong survival.

Antiretroviral Treatment (ART)

  • Highly active antiretroviral therapy (HAART) leads to viral suppression and improved patient outcomes.

  • Regimens include nucleoside and non-nucleoside reverse transcriptase inhibitors, protease inhibitors, and integrase inhibitors.

  • Ongoing monitoring and adjustments are essential to manage resistance.