18 Questions
What is the primary limitation of the Tzanck smear test in diagnosing HSV or VZV?
Poor sensitivity and specificity
What type of analysis can be used to detect the presence of specific viral proteins in tissue sections?
Immunohistochemistry
What is the term for the characteristic changes in cellular morphology caused by viral infections?
Cytopathic effect
What is the purpose of using tagged antibodies in immunohistochemistry?
To detect specific viral proteins
What type of viral diagnostic method involves the amplification of viral nucleic acid sequences?
Polymerase Chain Reaction (PCR)
What is the term for the accumulation of newly assembled virus particles in the cytoplasm or nucleus of infected cells?
Viral inclusion bodies
What is the primary purpose of the TCID50 assay in viral quantification?
To estimate the amount of infectious virus present in a suspension
What is the characteristic feature of owl's eye cells in CMV infection?
Nuclear and cytoplasmic inclusions
What is the primary method used to detect viral infection in the TCID50 assay?
Cytopathic effect
What is the purpose of serial dilution in the TCID50 assay?
To determine the infectious titer of a virus suspension
What is the characteristic feature of Negri bodies in rabies virus infection?
Found in the cytoplasm of nerve cells
What is the primary application of histopathology and cytopathology in viral diagnosis?
To analyze cellular morphology for viral infection
What is a limitation of conventional viral culture?
It requires significant technical expertise
What is the purpose of a phenol red indicator in cell culture medium?
To produce an obvious color change when the pH is out of range
What type of effect can viruses have on cultured cells?
Cytopathic effect
What is a benefit of viral culture compared to other diagnostic techniques?
It can be used for a wide range of specimen types
What is the purpose of a shell vial assay?
To detect viral antigens
What is the unit of measurement for quantifying viral growth?
Plaque-forming units (PFU)
Study Notes
Viral Diagnosis
- Pap smear can detect HPV, showing koilocytic atypia
- Parvovirus B19 can be detected by enlarged nuclei of erythroid precursors in a peripheral blood smear
- HSV can be detected by Tzanck smear of a lesion scraping, showing multinucleated giant cells
Morphologic Changes
- Some viruses produce characteristic changes to cellular morphology
- Changes can be highly specific for viruses, while others may overlap with other diseases or infections
- Confirm etiology with a more specific test
Viral Inclusions
- Newly assembled virus particles can accumulate in the cytoplasm or nucleus
- Aggregates of viruses and viral proteins can be seen as viral inclusion bodies
Immunohistochemistry (IHC)
- Tagged antibodies specific to certain viral proteins can detect specific viruses in tissue sections
Viral Quantification
- TCID50 assay estimates the amount of infectious virus in a suspension
- Serial dilutions of virus are used to infect cell monolayers
- The dilution at which there is no virus in 50% of replicates is the TCID50
Histopathology and Cytopathology
- Techniques used to detect viral infection by examining stained cells (cytology) or tissue sections (histology)
- Detects viral infection by characteristic inclusions or cell morphology
Histologic Identification of Viruses
- CMV: owl's eye cells with nuclear and cytoplasmic inclusions
- Parvovirus B19: enlarged ground glass nuclei in fetal liver
- Adenovirus: smudge cells in lung tissue
- Rabies virus: Negri bodies in the cytoplasm of nerve cells
- HSV: multinucleation, margination, and molding
- JC virus: ground-glass intranuclear appearance in oligodendrocytes
Culture and Tissue-Based Diagnostic Techniques
- Conventional viral culture can identify live viruses in various specimen types
- Cell lines are used to grow and amplify viruses in the laboratory
- Procedure involves inoculating the specimen onto a cellular monolayer
- Factors in cell culture medium include buffered medium, salts, amino acids, glucose, and vitamins
Identify the characteristic morphologic changes to cellular morphology caused by different viruses, including HPV, Parvovirus B19, HSV, and HTLV. Recognize the distinct features of each virus in blood smears and other diagnostic tests.
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