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USMLE Step I Microbiology > HIV > Flashcards

HIV Flashcards

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USMLE® Step 1 flashcards Biology 101 flashcards
1
Q

what kind of genome does HIV have?

A
  • diploid genome
    • 2 molecules of RNA
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2
Q

what are the 3 structural genes of HIV?

A
  • env (gp120 and gp41)
    • formed from cleavage of gp160 to form envelop glycoproteins
    • gp120–attachment to host CD4+ T cell
    • gp41–fusion and entry
  • gag (p24 and p17–capsid and matrix proteins, respectively)
  • pol–reverse transcriptase, aspartate protease, integrase
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3
Q

HIV–mechanism

A
  • reverse transcriptase synthesizes dsDNA from genomic RNA
  • dsDNA integrates into host genome
  • virus binds CD4 as well as a coreceptor
    • either CCR5 on macrophages (early infection)
    • OR CXCR4 on T cells (late infection)
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4
Q

HIV–homozygous CCR5 mutations

A
  • = immunity
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5
Q

HIV–heterozygous CCR5 mutation

A
  • = slower course
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6
Q

HIV–tests for diagnosis and pros/cons

A
  • presumptive diagnosis made with ELISA
    • sensitive
    • high false + rate
    • low threshold
      • rule out test
    • results are then confirmed with Western blot assay
      • specific
      • low false + rate
      • high threshold
        • rule in test
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7
Q

HIV–viral load

A
  • viral load tests determine the amount of viral RNA in the plasma
    • high viral load associated with a poor prognosis
  • also use viral load to monitor effect of drug therapy
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8
Q

AIDS–diagnosis

A
  • less than or equal to 200 CD4+ cells/mm3
    • normal is 500-1500 cells/mm3
  • HIV+ with AIDS defining condition (ie. Pneumocystis pneumonia) or CD4+ percentage <14%
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9
Q

what do ELISA/Western blot tests look for to diagnose HIV?

when may they give a false result?

A
  • ELISA/Western blot tests look for antibodies to viral proteins
  • often false - in first 1-2 months of HIV infection
  • often false + initially in babies born to infected mothers (anti-gp120 crosses placenta)
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10
Q

explain the time course of untreated HIV infection

A
  • Four stages of untreated infection:
    • Flu like (acute)
    • Feeling fine (latent)
      • during latent phase, virus replicates in lymph nodes
    • Falling count
    • Final crises
  • Most patients who do not receive treatment eventually die of complications of HIV infection
  • Graph:
    • red line = CD4+ T cell count (cells/mm3)
    • blue line = HIV RNA copies/mL plasma
    • blue boxes on vertical CD4+ count axis indicate moderate immunocompromise (<400 CD4+ cells/mm3) and when AIDS defining illnesses emerge (<200 CD4+ cells/mm3)
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11
Q

other diseases in HIV+ adults

A
  • as CD4+ cell count decreases, risks of reactivation of past infections (ie. TB, HSV, shingles), dissemination of bacterial infections and fungal infections (ie. coccidioidomycosis), and non-Hodgkin lymphomas increase
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12
Q

what are common pathogens in an HIV+ patient when CD4+ cell count < 500/mm3?

A
  • Candida albicans
  • EBV
  • Bartonella henselae
  • HHV-B
  • Cryptosporidium spp.
  • HPV
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13
Q

Candida albicans–presentation in HIV+ patients (CD4+ <500/mm3​)

A
  • oral thrush
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14
Q

Candida albicans–findings in HIV+ patients (CD4+ <500/mm3​)

A
  • scrapable white plaque
  • pseudohyphae on microscopy
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15
Q

EBV–presentation in HIV+ patients (CD4+ <500/mm3)

A
  • oral hairy leukoplakia
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16
Q

EBV–findings in HIV+ patients (CD4+ <500/mm3​)

A
  • unscrapable white plawue on lateral tongue
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17
Q

Bartonella henselae–presentation in HIV+ patients (CD4+ <500/mm3​)

A
  • bacillary angiomatosis
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18
Q

Bartonella henselae–findings in HIV+ patient (CD4+ <500/mm3​)

A
  • biopsy with neutrophilic inflammation
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19
Q

HHV-8–presentation in HIV+ patient (CD4+ <500/mm3​)

A
  • Kaposi sarcoma
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20
Q

HHV-8–findings in HIV+ patient (CD4+ <500/mm3​)

A
  • biopsy with lymphocytic inflammation
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21
Q

Cryptosporidium spp.–presentation in HIV+ patients (CD4+ <500/mm3​)

A
  • chronic, watery diarrhea
22
Q

Cryptosporidium spp.–findings in HIV+ patients (CD4+ <500/mm3​)

A
  • acid fast oocysts in stool
23
Q

HPV–presentation in HIV+ patients (CD4+ <500/mm3​)

A
  • squamous cell carcinoma
    • commonly of anus (men who have sex with men) or cervix (women)
24
Q

what are common pathogens in an HIV+ adult with CD4+ cell count < 200/mm3?

A
  • HIV
  • JC virus (reactivation)
  • pneumocystis jirovecii
25
Q

HIV–presentation in HIV+ patient (CD4+ <200/mm3​)

A
  • dementia
26
Q

JC virus (reactivation)–presentation in HIV+ patient (CD4+ <200/mm3​)

A
  • progressive multifocal leukoencephalopathy
27
Q

JC virus (reactivation)–findings in HIV+ patient (CD4+ <200/mm3​)

A
  • nonenhancing areas of demyelination on MRI
28
Q

Pneumocystis jirovecii–presentation in HIV+ patient (CD4+ <200/mm3​)

A
  • Pneumocystis pneumonia
29
Q

Pneumocystis jirovecii–findings in HIV+ patient (CD4+ <200/mm3​)

A
  • “ground glass” opacities on CXR
30
Q

what are common pathogens in HIV+ adults with CD4+ cell count <100/mm3?

A
  • Aspergillus fumigatus
  • Cryptococcus neoformans
  • Candida albicans
  • CMV
  • EBV
  • Histoplasma capsulatus
  • Mycobacterium avium–intracellulare, Mycobacterium avium**​ complex
  • Toxoplasma gondii
31
Q

Aspergillus fumigatus–presentation in HIV+ patient (CD4+ <100/mm3)

A
  • hemoptysis
  • pleuritic pain
32
Q

Aspergillus fumigatus–findings in HIV+ patient (CD4+ <100/mm3​)

A
  • cavitation or infiltrates on chest imaging
33
Q

Cryptococcus neoformans–presentation on HIV+ patient (CD4+ <100/mm3​)

A
  • meningitis
34
Q

Cryptococcus neoformans–findings in HIV+ patient (CD4+ <100/mm3​)

A
  • encapsulated yeast on India ink stain or capsular antigen +
35
Q

Candida albicans–presentation in HIV+ patient (CD4+ <100/mm3​)

A
  • esophagitis
36
Q

Candida albicans–findings in HIV+ patient (CD4+ <100/mm3​)

A
  • white plaques on endoscopy
  • yeast and pseudohyphae on biopsy
37
Q

CMV–presentation in HIV+ patients (CD4+ <100/mm3​)

A
  • retinitis
  • esophagitis
  • colitis
  • pneumonitis
  • encephalitis
38
Q

CMV–findings in HIV+ patients (CD4+ <100/mm3​)

A
  • linear ulcers on endoscopy, cotton wool spots on fundoscopy
  • biopsy reveals cells with intranuclear (owl eye) inclusion bodies
39
Q

EBV–presentation in HIV+ patient (CD4+ <100/mm3​)

A
  • B cell lymphoma
    • ie. non Hodgkin lymphoma, CNS lymphoma
40
Q

EBV–findings in HIV+ patient (CD4+ <100/mm3​)

A
  • CNS lymphoma
    • ring enhancing, may be solitary (vs. Toxoplasma)
41
Q

Histoplasma capsulatum–presentation in HIV+ patients (CD4+ <100/mm3​)

A
  • fever
  • weight loss
  • fatigue
  • cough
  • dyspnea
  • nausea
  • vomiting
  • diarrhea
42
Q

Histoplasma capsulatum–findings in HIV+ patient (CD4+ <100/mm3​)

A
  • oval yeast cells within macrophages
43
Q

Mycobacterium avium-intracellulare, Mycobacterium avium complex–presentation (CD4+ <100/mm3​)

A
  • nonspecific systemic symptoms
    • fever
    • night sweats
    • weight loss
  • focal lymphadenitis
44
Q

Toxoplasma gondii–presentation in HIV+ patients (CD4+ <100/mm3​)

A
  • brain abscesses
45
Q

Toxoplasma gondii–findings in HIV+ patients (CD4+ <100/mm3​)

A
  • multiple ring enhancing lesions on MRI
46
Q

Prion diseases–mechanism, transmission

A
  • prion dzs are caused by the conversion of a normal (pre-dominantly alpha helical) protein termed prion protein (PrPc) to a beta pleated form (PrPsc)
    • PrPsc is transmissible via CNS related tissue (iatrogenic CJD) or food contaminated by BSE-infected animal products (varian CJD)
  • PrPsc resists protease degradation and facilitates the conversion of still more PrPc to PrPsc
47
Q

Prion diseases–what is it resistant to

A
  • standard sterilizing procedures
    • including standard autoclaving
48
Q

Prion diseases–what does accumulation of PrPsc result in?

A
  • spongiform encephalopathy (A) and dementia
  • ataxia
  • death
49
Q

what are 3 diseases that result from prions?

A
  • Creutzfeldt-Jakob disease
  • Bovine spongiform encephalopathy
  • Kuru
50
Q

Creutzfeldt-Jakob disease

A
  • rapidly progressing dementia
    • typically sporadic (some familiar forms)
51
Q

Bovine spongiform encephalopathy (BSE)

A
  • also known as “mad cow disease”
52
Q

Kuru

A
  • acquired prion disease noted in tribal populations practicing human cannibalism

USMLE Step I Microbiology (44 decks)

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