S1B4 - Study Questions 02 Flashcards
Which are the smallest DNA and RNA viruses?
Parvovirus B19 is the smallest DNA virus and picornaviridae are the smallest RNA viruses.
What are the 3 signs of viral infection?
SIGNS OF VIRAL INFECTION
A virally-infected cell generally presents three signals that it is infected.
- The production of double-stranded RNA, which induces interferon
- The expression of viral protein on the surface of the plasma membrane, thus causing activation of cytotoxic T-cells, natural killer cells and sometimes induction of antibody synthesis.
- The formation of an inclusion body either within the cytoplasm or the nucleus or very rarely within both the cytoplasm and nucleus.
What are CPE, Negri bodies?
CYTOLOGY.
Observation of virus-induced cytopathologic effects (CPE) on cells, e.g., inclusion bodies (Cowdry type A nuclear inclusion bodies, Negri bodies, nuclear owl’s eye inclusions), cell lysis, vacuolation, syncytia (multinucleated cells formed by cell fusion).
Differentiate hemagglutinins from hemagglutination?
VIRAL DETECTION.
CPE – inclusions, plaques or other cytopathologic effects may be characteristic of certain viruses. Although rubella virus doesn’t produce obvious CPE, its presence can be suggested by its ability to interfere with picornavirus replication in a process known as heterologous interference. Cells infected with influenza, parainfluenza, mumps or togavirus, express hemadsorption receptors on their cells surfaces. These receptors (hemagglutinins) cause erythrocytes to bind to each other (hemagglutination), which can be used diagnostically. Even more useful is a process known as Hemagglutination Inhibition, whereby the use of the appropriate specific antibody can block the hemagglutination and identify the viral agent causing the hemagglutination.
Differentitate LD50 from ID50
Viral quantization
- Tissue culture dose (TCD50) – the titer of virus causing CPE in 50% of the tissue culture cells
- Lethal dose (LD50) – the titer of virus killing 50% of the test animals.
- Infectious dose (ID50) – the titer of virus infecting 50% of the test animals.
- Plaque-forming units – the concentration of particles (or units) capable of producing a hole (absence of abundant growth) in a bacterial lawn or tissue culture monolayer. CPE can also be the end-point in this calculation.
What is the meaning of seroconversion and how is it calculated?
Virus-specific seroconversion – a 4-fold increase in titer between acute and convalescent phases (~3 weeks apart)
Differentiate Type II and Type III hypersensitivity and the role they play in host damage?
Type II hypersensitivity – IgG and/or IgM antibodies are involved in this reaction. The effects can be of two types: The virus (or viral component) - complement - antibody complex is fixed to a cell, usually an erythrocyte or leukocyte or platelet, resulting in complement-dependent cell lysis. This is the pathogenic mechanism in many viral diseases where anemia is one of the clinical manifestations. Similarly, a virus component, commonly the capsid protein, may be expressed on the surface of the infected cell. Antibody and complement bind to this infected cell and cause a lysis of that cell. This is thought to be the major mechanism of viral-induced cell lysis in tissues.
Type III hypersensitivity – (Uncommon) IgG and/or IgM antibodies form complexes with viral antigen and complement, generating neutrophil chemotactic factors, with resultant local tissue inflammation and destruction. Although much rarer, some viral diseases may result in a generalized rather than localized tissue destruction. This type of disease is a multi-system complement-dependent vasculitis in which immune complexes are deposited along the endothelial surfaces of blood vessels, stimulating inflammation and vascular wall damage.
How does a virus play a role in cancer; what is transformation?
Cell transformation - Certain viruses have the ability to enter a cell and follow one of two alternative courses. They either multiply in a normal manner and are eventually released from the cell, or they may be dormant in the cell and eventually transform the cell into a malignant cell. It is believed that the transformation process involves the integration of viral nucleic acid into the host chromosome. When this happens, the cell achieves certain characteristics of malignant cells.
What kinds of cytoplasmic changes are caused by myxoviruses, rabies virus and poxviruses?
Cytoplasmic changes
- RNA viruses, e.g., rabies, can produce a large eosinophilic mass in the cytoplasm.
- Myxoviruses (e.g., influenza) cause cytoplasmic vacuolization, contraction and degeneration. “Buds” appear on cell surface.
- Myxoviruses (mumps) cause eosinophilia and Feulgen-negative cytoplasmic inclusions.
- Reovirus and measles virus cause eosinophilia.
- Poxviruses cause formation of Feulgen-positive cytoplasmic inclusions, which contain virions.
- Herpesvirus causes vacuolization.
What kinds of nuclear changes are caused by rabies virus, herpesvirus, adenovirus, poxvirus and measles virus?
Nuclear changes
- Pyknosis (nucleus pushed to eccentric position in cell); e.g., a rabies virus inclusion body.
- Nuclear inclusion (bodies in the nucleus); e.g., herpesvirus, adenovirus.
- Margination and coarsening of chromatin; e.g., herpesvirus, poxvirus.
- Polykaryocytosis (many nuclei in the same cytoplasmic field); e.g., herpesvirus and measles virus.
How do viruses affect host cell membranes? What problems can arise for the cell?
Membrane changes
The human cell membrane is a dynamic structure continually changing in lipid and protein content during normal cellular growth and division. Viral infection of the cell often results in viral protein being incorporated into this membrane. These changes can lead to production of antibodies against the cell membrane and lysis of this membrane.
What does the presence of virus-specific IgM indicate?
Virus-specific IgM indicates recent infection.
