ZO 2.5 Virology Flashcards
Wat betekend tropisme?
Virus tropism refers to the range of specific cell types within a single species that a virus can infect and replicate in.
Welke factoren spelen een rol bij tropisme?
Other important factors for host range and tropism are the availability of certain transcription factors and environmental requirements such as temperature and pH. For a large part, this explains why, for example, plant viruses do not infect humans and vice versa. Cellular tropism can also determine the host range of a virus.
Hoe kunnen we virussen detecteren en identificeren?
To be able to detect a virus and to identify a specific virus we focus on virus-specific components such as:
- Specific viral proteins that are not expressed by the uninfected host;
- Virus genome, or parts of the virus genome
As mentioned before, a virus contains either DNA or RNA. RNA and DNA are also expressed by the host but viral DNA and RNA can be identified by specific sequences that can be detected using molecular techniques.
Welke twee typen testen zijn er voor het detecteren van een virus infectie?
- Direct tests: tests that detect (components of the) viral particle. Direct diagnostic tests detect the virus or a component of the virus particle such as viral protein, viral antigen, viral genome or the cytopathic effect (CPE).
- Indirect tests: tests that measure the host immune response to the viral infection. Indirect diagnostic tests detect the response of the immune system to the virus: the induction of virus-specific antibodies which can be measured in plasma and other body fluids.
Welke testen zijn er om virussen direct te detecteren?
- PCR (Polymerase chain reaction)
- EIA
- Immunoblot
- Agglutination Assay
- Immunofluorescence
- EM (Electron Microscopy)
- CPE (Cytopathic effect) - if the virus can be cultured
Welke testen zijn er om virussen indirect te detecteren?
Detection of virus-specific antibodies via EIA, Immunoblot, Agglutination assay or Immunofluorescence. EIA, Immunoblot, Agglutination Assay and Immunofluorescence all belong to the group of Immunoassays.
Wat zijn immunoassays?
Immunoassays are laboratory techniques that make use of the binding between an antigen and its homologous antibody in order to identify and quantify the specific antigen (for direct detection) or antibody (for indirect detection) in a sample
Hoe werkt enzyme immune essays?
EIA stands for Enzyme Immuno Assay; it is a laboratory technique that is based on the specific binding of antibodies to antigens. To detect virus in patient material, antibodies are used which specifically bind to a viral protein (antigen). By immobilizing these antibodies to a test plate, the virus can be captured from the sample and presence of the specific viral antigen can be detected using additional specific antibodies that are linked to an enzyme that can induce a color change of the transparent substrate. This way, minute amounts of viral antigen from patient material can be detected and quantified. Besides viral antigens (direct detection), this technique can also detect virus-specific antibodies (indirect detection).
Hoe werkt een immunoblot voor direct virus detectie?
With this technique, viral proteins can be detected in a sample by first separating these proteins using gel electrophoresis resulting in different bands of proteins. These proteins are transferred to a nitrocellulose membrane. This process is also known as ‘blotting’, hence the term Immunoblot.
Next, antibodies directed against the suspected virus are allowed to incubate with the Immunoblot. If the specific virus protein is present, they are bound by the antibodies which can be detected with various methods, leading to the appearance of bands.
Hoe werkt een immunoblot voor indirecte virus detectie?
The virus-specific proteins are already blotted to a membrane. Next, the sample, usually serum, is added to the membrane. If the sample contains virus specific antibodies the antibodies will bind to the protein blotted on the membrane. Next, these virus-specific antibodies are detected using specific antibodies directed against the human antibodies. Depending on the available virus specific proteins it is possible to specify virus species and even virus subtype.
Hoe werkt de agglutination assay?
This technique uses small beads coated with virus-specific antibodies. If a sample contains the virus to be detected by these antibodies, binding of the virus by the beads results in agglutination of the beads which can be seen by the naked eye. Besides viral antigens (direct detection) this technique can also detect virus-specific antibodies (indirect detection).
Hoe werkt immunofluorescentie?
Immunofluorescence is a technique that, similar to EIA, uses specific antibodies to detect viral protein in patient material or virus cultures. Detection is facilitated by the labelling of the antibody with a fluorescent dye that is detected using fluorescence microscopy. We distinguish between direct immunofluorescence: the specific antibody is (directly) labelled from indirect immunofluorescence: The specific antibody binding the viral protein is detected by a labelled secondary antibody.
Wat is CPE?
The cytopathic effect (CPE) is the change in cell morphology that occurs as a consequence of the presence and replication of the virus in the cell. The type of CPE is specific for the type of cell-line and virus. Not all viruses generate a CPE.
Welke verschillende containers zijn er om bloed in te vervoeren?
Blood samples delivered in several types of containers:
- Stolbloed/serum (Eng: ‘clotted’)
- EDTA-bloed/plasma (Eng: ‘EDTA-treated’)
- Heparine-bloed/plasma (Eng: ‘Heparin-treated’)
These samples are to be collected via a venipuncture in a tube.
Welke samples zijn geschikt voor virologie diagnose?
- All fluids and swabs, as long as transport medium is used.
- Dry swabs cannot be used when cells are required to execute the diagnostic test. (Extra explanation: without fluid, the cells you collect with the swab will die rendering the sample unfit for diagnostic tests that require cells).
- Blood samples containing heparin cannot be used for testing with PCR. (Extra explanation, the heparin inhibits the PCR reaction leading to false negative results).
