Slow Virus Infections, Bacteriophages, Serology for Viruses Flashcards
What are the “conventional” slow virus infections?
4 are listed
- SSPE: Subacute Sclerosing Pan-encephalitis (Dawson encephalitis) following years of measles infection. Chronic CNS degeneration.
- PML: Progressive Multifocal Leukoencephalopathy from JC virus (a polyomavirus). Infected oligodendrocytes -> demyelinating of CNS. Mainly in immuno-compromised.
- Post-rubella panencephalitis
- Persistent enterovirus infections
What are the “unconventional” slow virus infections?
They’re not even viruses but prion diseases, so it’s an outdated classification system (although apparently some researchers believe the prion diseases are caused by still-undiscovered viruses)
-Spongiform encephalopathies: kuru, Creutzfield-Jakob, vCJD, BSE, Gerstmann - Straussler - Sheinker, Familial Fatal Insomnia. Fatal, no recovery, no treatment. Prions are infectious proteins that destroy other proteins of the CNS.
What are some features of slow virus diseases?
- Typically asymptomatic primary infection. Extended period of latency, progressive course from months to years
- Immune system fails to protect against it
- No treatments exist, just prevention (Vaccines for measles, rubella. Autoclave for prions)
Bacteriophages
- Structure, morphology
- 2 types of phages
- dsRNA or DNA, ssDNA. Special “syringe-like” structures to bind cell receptors and inject phage nucleic acid in host cell
1. Lytic Phages: produce many copies of themselves and kill host cells (for example E. coli T-even phage)
2. Temperate Phages: able to enter a non-lytic prophage stage, replicate their nucleic acids (for example E. coli lambda phage). If bacteria contains it, it’s called a “lysogenic bacteria.” A signal can cause the virus to enter a lytic cycle.
Bacteriophages:
-What is transduction?
-Transduction: transfer of cell DNA by means of bacteriophage. The phage is a vector in this case.
Bacteriophages:
-What is bacteriophage typing? How is it performed?
- Categorizing bacteria based on their susceptibility to bacteriophages. Done for epidemiological studies, especially S. aureus and Salmonella.
- Surface plate is innoculated and various phages are spotted around the plate. After incubation, the phage type is determined by the pattern of lysis.
- If the lytic pattern is the same = “clonal spreading” has occurred.
Bacteriophages:
Besides phage typing, what are some other uses for bacteriophages?
- Therapy: used somewhat like antibiotics but even more specific, harmless to human. May be too specific to certain strains to actually end an infection though. May work when there is a biofilm layer that antibiotics have trouble penetrating
- Biotechnology: phages used as vectors to insert DNA as needed
Bacteriophages:
-What is the phage titer-elevation reaction?
Phage titer rises in the presence of a homologue bacterium
i don’t really get what this means but was mentioned by the department, hopefully it’s nothing
Virus Serology:
-General concepts for IgM and IgG detection
-IgM usually indicates newer infection, IgG indicates that the virus must have been around long enough to seroconvert. If negative for IgM and positive for IgG = “convalescent” stage.
Virus Serology
-Typical methods for detecting serum antibodies against viruses
- Indirect ELISA: antigen stuck in tube, add serum, wash, add secondary antibody against the serum antibodies and the secondary Ab is somehow labeled/identifiable (e.g. HRPO)
- Sandwich ELISA: antibody is stuck to tube, add serum maybe containing antigens (in this case the antigens can be serum antibodies), wash, and then add identifiable antibodies
- Competitive ELISA: antigen attached to tube, add serum + labeled antibodies together, add chromogenic substrate. Amount of color is inversely proportional to amount of antibody in test specimen
- Complement Fixation: take patient serum, remove complement, replace with standardized complement. Add antigens to serum, then add sheep RBCs that have been pre-bound to antibodies. If serum has the Ab you want, then complement is used up by first Ag-Ab rxn and there will be no cell lysis. If there are no Ab, then complement remains to lyse the sheep RBCs.
- HAI: Hemagglutination inhibition test (described later)
Virus serology:
-Relevance to hepatitis viruses
- HAV: IgM for acute, IgG probably means either vaccinated or the infection has been resolved
- HBV: just look at the hepatitis cards, this one is too detailed
- HCV: IgG used for HCV screening, confirm with PCR
Virus serology:
-HIV
-HIV-1 and HIV-2 have serology tests where there is a notable initial window period of negative results. Tests should be repeated if HIV is suspected. Most patients seroconvert within 3 months. Positive results confirmed with Western blot.
Virus serology:
- EBV
- Rubella
- Parvovirus
- EBV in infectious mononucleosis gets special Paul-Bunnel monospot test where the person has non-specific antibodies that can agglutinate sheep RBCs
- Rubella: test for IgM in pregnancy because acute infection is major risk
- Parvovirus: same, really applies to any TORCH infection
Virus Serology:
Hemagglutination (HA) and Hemagglutination Inhibition (HAI) Tests for viruses:
-HA: some viruses have surface proteins which agglutinate RBCs (influenza binds sialic acid receptors). Dilutions are made which indicate the lowest concentration of virus to cause hemagglutination
HAI: antibodies against influenza prevent it from attaching to RBCs, so you basically do the same but with serum to see if it contains antibodies (no hemagglutination present) vs no antibodies (hemagglutination present)
Virus Serology
-HAI test for Rubella
- Some ancient test for Rubella that is certainly not used anymore but they maybe want us to know
- Have parallel dilution test: “T” for total and “M” Meritett (exhausted) that contains SAP Staphylococcal Protein A to bind to IgG, making a complex that sediments after centrifugation.
Evaluation:
-(T) neg (M) neg = no antibodies, susceptible
-(T) pos (M) neg = only IgG present, immune
(T) pos (M) pos = fresh infection, has IgM too. Major problem for fetus if seen in pregnant women
