Updated: 5/27/2017

Human Immunodeficiency Virus / Acquired Immunodeficiency Syndrome

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Overview
 

 
Snapshot
  • A 24-year-old man presents to his primary care physician with fever, headache, sore throat, and myalgias. He reports his symptoms began a few days ago and believes it is from a "cold." Social history is significant for having multiple male partners. He does not consistently use condoms. His last sexual encounter was 2 months ago. Physical exam is significant for cervical lymphadenopathy. An HIV-1/2 antigen/antibody combination immunoassay is positive for p24 antigen and an elevated HIV viral load. HIV-1/2 antibody differentiation immunoassay shows that he is solely HIV-1 reactive.
Introduction
  • Human immunodeficiency virus (HIV), an RNA retrovirus, can result in
    • acquired immunodeficiency syndrome (AIDS) via
      • gradually losing competence of the host's immune system, which results in
        • opportunistic infections such as
          • Pneumocystis jiroveci
          • Toxoplasma gondii
          • Mycobacterium avium-intracellulare
          • HHV-8
  • Pathogenesis
    • HIV infects CD4+ cells via binding to the CD4 receptor and
      • co-receptors such as
        • CCR5 on macrophages
          • in early infection
          • clinical correlate
            • homozygous CCR5 mutations leads to
              • immunity against HIV infection
            • heterozygous CCR5 mutations leads to
              • a slower infectious course
        • CXCR4 on T cells
          • in late infection
    • the infected cells (CD4+ T-cells, dendritic cells, and macrophages) eventually serve as a resevoir for the virus which
      • delivers the virus throughout the body
  • HIV structure
    • the viral particle contains
      • two copies of an RNA genome as well as
        • gp120 and gp41
          • result from the cleavage of
            • gp 160
          • arise from the env gene
          • gp120
            • allows for the attachment to
              • the host's CD4+ cells
            • allows for antigenic drift leading to
              • evasion of antibody-mediated destruction
          • gp41
            • allows for viral
              • fusion and entry into the host cell
        • p24 and p17 arise from the
          • gag gene and serves as
            • the viral capsid (p24) and
              • viral matrix protein (p17)
        • the pol gene leads to the synthesis of
          • reverse transcriptase which
            • synthesizes dsDNA from
              • RNA in order to
                • integrate the reversed transcribed viral DNA into host's DNA
          • aspartate protease
          • integrase which
            • integrates the reverse transcribed DNA into the host's genome
  • Diagnosis
    • HIV-1/2 antigen/antibody combination immunoassay
      • if positive for HIV-1/2 antibodies or HIV p24 antigen then
        • perform an HIV-1/2 antibody differentiation immunoassay
    • viral load
      • determines the
        • HIV RNA amount in the patient's plasma
 
Opportunistic Infections Based on CD4+ Cell Count
Cell Count (cells/mm3)
Pathogen & Disease(s)
< 500/mm3
  • Candida albicans
    • oral thrush
  • Bartonella henselae
    • bacillary angiomatosis
  • Epstein–Barr virus (EBV)
    • oral hairy leukoplakia
  • HHV-8
    • Kaposi sarcoma
  • HPV
    • squamous cell carcinoma of the anus and cervix
< 200/mm3
  • Pneumocystis jirovecii
    • pneumonia
  • Reactivation of the JC virus
    • progressive multifocal leukoencephalopathy
  • Histoplasma capsulatum
    • nonspecific symptoms such as
      • fever, weightloss, and cough along with
        • oval yeast cells within macrophages
< 100/mm3
  • Candida albicans
    • esophagitis
  • Aspergillus fumigatus
    • hemoptysis and pleurisy
  • Mycobacterium avium-intracellulare and mycobacterium avium complex
    • nonspecific findings such as
      • fever, weight loss, and night sweats
  • Toxoplasma gondii
    • brain abscesses that can appear as
      • ring-enhancing lesions on MRI
  • Cryptococcus neoformans
    • meningitis
  • Cryptosporidium species
    • watery diarrhea
  • Epstein–Barr virus (EBV)
    • B-cell lymphoma
  • Cytomegalovirus
    • retinitis
    • esophagitis
    • colitis
    • encephalitis
    • pneumonitis
 
 

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