Viro - Midterm 1

drraythe's version from 2015-08-30 21:41

Viral identification + Epidemiology

Question Answer
If tissues are sampled (biopsy or necropsy) w/ the purpose of viral detection, what should you not do?Place them in fixatives (like formalin)
What conditions should you keep viral samples in? What should you NOT do?Want them cold & moist, but DONT freeze them!
Define sensitivity(% of true positives) % of animals w/ the dz that test positive w/ the test divided by the total number of infected animals
Define specificity(False positive rate) % of healthy animals which test negative by the test divided by the total number of infected animals
Examples of direct examination of virusesElectron microscopy
Light microscopy
Antigen detection
Viral genome detection
Examples of indirect examination of virusesCell culture, embryonated eggs, animals, serology (growin em, looking for results of em)
How many virus particles per mL are required to visualize in a sample w/ electron microscopy? What are the three most common samples?10^6 virus particles per ml required for visualization. Can be feces, vesicle fluid, & skin scrapings
Disadvantages of electron microscopy?1) Expensive equipment
2) Expensive maintenance
3) Require experienced observer
4) Sensitivity often low
How can you ↑ the sensitivity & specificity of electron microscopy?Immune Electron Microscopy
What is an extremely sensitive technique to detect viruses? HOW sensitive?Polymerase Chain Rxn (PCR). PCR allows the in vitro amplification of specific target DNA sequences by a factor of 10^6 & is thus an extremely sensitive technique
Disadvantages of PCR?1) Extremely liable to contamination
2) High degree of operator skill required
3) Need to set up a quantitative curve
4) A positive result may be difficult to interpret, especially w/ latent viruses.
What is still the most common way to amplify/isolate viruses?Cell culture! (Cheap & easy) → form a monolayer on a plastic dish
What are the three types of cell cultures used?1) 1⁰ cells – ex. cells are harvested from tissues such as monkey Kidney (best bc support widest variety, but expensive & difficult to get/maintain)
2) Semi-continuous cells – ex. Human embryonic kidney & skin fibroblasts
3) Continuous cell lines –these are usually transformed & immortal (easiest to handle but limited viruses can grow on it)
Difference between a susceptible cell line & a permissive/non-permissive cell lineSusceptible = virus can infect it
Permissive = allows virus to get in, & has everything virus needs to complete a whole cycle of replication
What two changes might the virus produce in the cells of the cell culture?1) Cytopathic Effect (CPE) (such as the ballooning of cells or syncytia formation, may be specific or non-specific)
2) Hemadsorption - cells acquire the ability to stick to mammalian red blood cells
Some disadvantages of cell culture?LONG PERIOD for growth. Bacterial contamination. Sensitivity depends on condition of specimen. Some viruses dont grow in culture. Mixed infxns = difficult to isolate
If you are using an embryonated egg as a cell culture, what you gotta know?Diff types of viruses need to be injected into diff locations
How would you use a mouse as a virus culture medium?Day old mice inoculated intracerebrally or intraperitoneally
Using serology for Ab detection of viruses → what do you need to know about the IgG stuff? IgM stuff?Initial infxn = 4 fold or more ↑ in titer of IgG or total antibody between acute & convalescent seroconversion. A single high titer of IgG is very unreliable. The presence of IgM is quicker than waiting the two weeks for the IgG, & is a good indicator.... 1 fold increase = reinfxn
Know chart on the top of p 15IgM first to react, IgG takes like 2 weeks but get a stronger response, if reinfxn IgG was already raised from first infxn so then it goes WAYYYYY up, IgM might not even react or will only react a little
What are the criteria for diagnosing a reinfxn?1 fold or more increase in IgG/ total Ab titer between the acute & convalescent seroconversion, OR absence/slight ↑ in IgM
What is Hemagglutination inhibition?Virus specific antibodies will interfere w/ the capacity of the virus to agglutinate RBCs
What are the disadvantages of serology? (6)(1) Long period of time required for diagnosis for paired acute & convalescent sera
(2) Mild local infxns may not produce a detectable humoral immune response
(3) Extensive antigenic cross-reactivity between related viruses → false positives
(4) Immunocompromised patients often give a reduced or absent humoral immune response
(5) Patients given blood or blood products may give a false positive result due to the transfer of antibody
(6) Neutralizing antibodies can only be tested in cell culture, therefore cannot be identified in un-culturable viruses
Summary of detection & identification of viral antigensEnzyme immunoassay methods (ex. Antigen ELISA ), Immunochromatography, Immunofluorescence (IF), Immunohistochemistry (IHC), Immunoelectron microscopy (IEM), Latex particle agglutination
Summary of Direct detection & identification of viral nucleic acidPCR (polymerase chain rxn), RT-PCR & sequencing, in situ hybridization, Southern blot & dot blot, fingerprinting & restriction enzyme mapping
Summary of Virus isolation & identificationVirus isolation in animals & chick embryos, virus isolation in cultured cells, virus quantification (plaque assay)
Summary of Detection & quantification of antiviral antibodiesEnzyme immunoassay methods (ex. Antibody ELISA , Serum neutralization assay (SN), Immunoblotting (Western Blot), Indirect immunofluorescence (IFA), Hemagglutination inhibition assay (HI)
IncidenceFrequency of a dz in a population in a specific period of time
PrevalenceFrequency of a dz in a population at a moment of time
Morbidity% of animals that get sick of a particular dz
EpidemicNumber of cases that exceed the expected number for a particular dz
EndemicContinuous occurrence of a particular dz in a population (area)
AnthropozoonosisAny dz that is transmitted from animals to insect vector to humans.
Arboviral dzWhen an insect vector is involved & the virus replicates in the vector! Some viruses may be mechanically transmitted by vectors but these are not arboviruses
Zoonosis vs anthropozoonosis, vs arboviral dzZoonosis is when Zoonoses are dzs of vertebrate animals that can be transmitted to man: either directly or indirectly through an insect vector & vice versa (anthropozoonosis)When an insect vector is involved & the virus replicates in the vector, the dz is also known as an arboviral dz. Some viruses may be mechanically transmitted by vectors but these are not arboviruses However, not all arboviral dzs are zoonoses: where the transmission cycle takes place exclusively between insect vector & human (dengue) (SO...zoonosis = between animal & man. anthropozoonosis is between animal & man via insect vector. & arboviral is when the virus needs to replicate in the insect as part of the lifecycle, & can be transmitted to man, but isnt necessarily a zoonosis, can just be between insect & man)


Viral Families, Herpesviridae

Question Answer
Enveloped or not? Implication of this?Enveloped → not resistant in enviro → need close contact to spread
Important characteristic of this family?All hosts become latent carriers
Where does it replicate? How can you identify it from this?Nucleus, they leave typical intranuclear inclusion bodies
Some Diagnostics tests to detect Herpesviruses?Observation of intranuclear inclusion bodies & sometimes syncytia in tissues, serology & viral isolation
Are there vx for Herpes?For most yes, sometimes theyre only protecting against the dz & not the infxn tho
Some clinical signs it may showWide variety of clinical signs ranging from CNS to Abortions, mucosal/skin lesions, ocular lesions, respiratory or GI dzs, Neoplasias, etc

Viral Families, Adenoviridae

Question Answer
Enveloped or not?NAKED! Penton fibers cover it though. Bc naked → resistant in enviro → indirect xmission common
Unique things about this group? (3)PENTON FIBERS, & Intranuclear inclusion bodies are found sometimes forming large Paracrystalline arrays of viral particles, & they agglutinate RBCs
Clinical signs of Adeno?Clinical signs are usually respiratory in most species but can also include hepatitis, death & decline in egg production
Diagnostic tests?PCR or serology, HI & viral isolation.
Are there vx for Adeno?There is a vaccine for CAV & egg drop syndrome

Viral Families, Papovaviridae

Question Answer
DNA or RNA?DNA, circular
Enveloped or not?Naked, but direct contact usually required for transmission
Clinical signs of Papova?Warts on the skin & nucleus
Diagnostic tests?Diagnostic tests are not usually required. EM or PCR can be done. Papillomaviruses DO NOT grow in cell culture
Are there vx for Papova?Yes, vx & auto vx
Unique things about this family?Naked but need direct contact, circular DNA, dont usually need diagnostic tests, & dont grow in cell culture

Viral Families, Parvoviridae

Question Answer
DNA or RNA?SS DNA, neg. Replication occurs in the **nucleus of dividing cells** & leave large intranuclear inclusion bodies
Enveloped or not?NAKED, stable in enviro, resist 60ºC for an hour & pH 3 to 9!
Clinical signs?Clinical signs are ataxia (kittens) vomiting & diarrhea (dogs), SMEDI (swine) but all species have PankLeukopenia.
Diagnostic tests?Diagnostic tests are antigen ELISA , PCR, HA. Serology is not very useful bc seroprevalence is very high in swine & the speed & fatality of the dz in cats & dogs
Are there vx?There are vaccines but maternal antibodies usually interfere (importance of timing & boosters)
Unique things about this family?REPLICATES IN DIVIDING CELLS!! Intranuclear inclusion bodies. Hemagglutinate. Causes Panleukopenia in all species, SEROLOGY NOT USEFUL!! Only affects CEREBELLUM, NOT THE WHOLE BRAIN

Viral Families, Coronaviridae

Question Answer
Enveloped or not?ENVELOPED, w/ large, club shaped peplomeres. Despite being enveloped it is moderately resistant in the environment, therefore both direct & indirect transmission is observed
Clinical signs?In general these viruses cause respiratory & gastrointestinal dzs in many species but can also affect the CNS or the reproductive system.
Are there Vx?Vaccines are not always effective & local immunity (mucosal IgA) is more important that systemic IgG. Vaccination of the dam to pass maternal antibodies in colostrum & milk is more effective than vaccinating the young
Unique things about this family?Club shaped peplomeres. Enveloped but resistant enough to be direct or indirect xmission. IgA more important than IgG, so Vx always not the best (more effective to vx dam)

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