Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Micro > Lecture 12 > Flashcards

Lecture 12 Flashcards

1
Q

what is a virus

A

-nonliving
-obligate intracellular parasites
-must use host cells to reproduce
-can infect any living organism including bacteria (bacteriophage)
-very small need an electron microscope
-study of viruses and the diseases they cause is called Virology

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Viral Structure

A
  • Entire structure called a virion
  • Genome can be RNA, DNA, ds or ss surrounded by Capsid made up of capsomere units
  • Capsid + genome= nucleocapsid
  • Can be naked or enveloped

Envelope- extra coat outside the capsid
-Made of host cell lipid membrane
-provide shape
* Some virus have glycoprotein spikes found on the envelope that are used to attach to cells

Envelops make the virus more susceptible to killing by disinfectants in pH or temp

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Viral Classification/Taxonomy

A

Classification based on:
a) Morphology:
* Size and shape of capsid
* Presence or absence of envelopes

b) Type of genome
* DNA or RNA (double stranded/ds or single stranded/ss)

Taxonomy:
Family = viridae→ Papovaviridae
Genus = virus→ Papillomavirus

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Viral Replication
Infectious

A
  1. Attachment or Absorption
    * Recognition, binding to a specific host cell receptor
    * Attachment via adhesion molecules, for example, spikes
  2. Penetration – Entry into the host cell
    * Fusion with cell membrane (enveloped viruses)
    * Endocytosis (enveloped & naked viruses enter via cytoplasmic vacuole)
    * Direct penetration of cell membrane
    (naked virion
  3. Uncoating & Genome replication/Biosynthesis
    * inside the virus loses protein coat (capsid)
    * Release of viral RNA (in host cytoplasm)
    * Or DNA (in host nucleus)
    * The viral genome directs host to replicate & reproduce the viral genome & the proteins to make a new capsid
    * Host cell metabolism may stop or continue, on a restricted scale
  4. Assembly (maturation of the virus)
    * Assembly into a complete viral particle (virion)
  5. Release – Exit from the host cell – infect other host cells
    * Lysis of host cell – host cell is killed (naked virus)
    * Bud through cell membrane – cell intact (enveloped virus) - host not killed. only for enveloped virus enters by fusion and exits by budding
    * Exocytosis – host cell intact (enveloped virus) -host not killed - through a vacuole
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

ways of Viral Transmission

A

Droplet: respiratory route, cough or sneeze

Fecal/oral: improper hand washing or ingestion of contaminated food or water

Sexual: vaginal or anal sex (exchange of body fluids, infected sores, kissing)

Touching contaminated objects

Vector borne

Transplantation: organ or blood

Gestational (transplacental)

Trauma or needle stick injury

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Lysogenic cycle:

A
  • Virus genome not immediately replicated, -becomes incorporated into host genome
  • Replicates with host cell but is not expressed - can last for many years (latency). Virus can be reactivated to go into the lytic cycle
  • Examples: HIV- CD4 lymph , Herpes
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Lytic cycle:

A

replication of viral genome in host cell- cell death due to the virus lysing the cell as it exits
* Or cell gets damaged/dies due to diversion of energy, competition for enzymes or mutations to host genome
* Examples: SARS, Influenza virus & intestinal viruses

Once the virus is out itll spread to body and target organs. This affinity for specific tissue is TROPISM
-Viral symptoms are only clear when there is an immune response and cell/tissue damage.
-the last stage of pathogenesis would be the virus concentrating in sites where it could be shed or passed on

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

VIRAL ANTIGENS

A
  • surface AG that are part of the strcuture
    -AG that illicts an immune response - protein AG
    FLU - Hemagglutinate ag - N spikes and H spikes
    muramidase ag
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

VIRUS GENOME MUTATIONS

DNA vs RNA mutations

A
  • Host cell can sometimes change its receptor site so virus can’t attach anymore. This is where the mutations come it so the virus can adapt or itll be killed by an AB
  • DNA viruses have less mutations because replication of DNA includes a proof reading step by the exonuclease enzyme
  • RNA viruses like influenza & COVID 19 have increased chance of mutation
  • Because RNA replication does not include a proof reading step
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Influenza VIRUS MUTATIONS

A
  • when genomes or AG are altered causing non immune hosts to be infected
    -types A/B are most important because they can mutate and cause epidemics while C cannot . A mutates faster than B.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Influenza A subtypes more than 18 are based on changes to its:

A
  • H antigen: hemagglutin (binds to host cell)
  • N antigen: neuraminidase (cleaves budding viruses from infected cell

Influenza B subtypes are based on changes to its:
* H antigen only - Only 2 subtypes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Antigenic drift:

A
  • Minor slow mutation in H & N antigens
  • Due to errors in replication of genome
  • Immunized hosts are no longer immune to the new strain because Ab’s & previous vaccinations do not match
  • Result is mild flu outbreak every 1-3 years (occurs with influenza A, B)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Antigenic shift:

2 MECHANISMS of ANTIGENIC SHIFT

A
  • Major abrupt change caused when different strains of virus combine their genomes
  • result in new H & or N antigens (occurs only with A)
  • May result in a pandemic
  1. Genetic Reassortment:
    * All influenza infect birds, but some infect pigs or other mammals
    * Pigs have receptors for avian, swine and human virus- can be co-infected with all 3 strains
    * RNA genome become mixed into a single virion = new strain of influenza virus – example H1N1 pandemic in
    2009
  2. Adaptive mutation:
    * Virus adjusts slowly due to increased proximity or mutations that overcome host barriers
    * New strain becomes transmissible from one mammal to another - Crosses the species barrier -H5N1 Bird flu pandemic (jumped from birds to humans)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Acute

Persistent

Chronic infection

A

Acute infection:
* Rapid onset of disease, immune system fights with in usually within days
* can result in death

Persistent infection:
* Long term infection
* chronic, latent or slow

Chronic infection:
* A kind of persistent infection - starts with an acute infection and then stays
* Continued symptoms or reoccurring symptoms

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Latent infection:

Slow infection

Transformation:

A

Latent infection:
* A type of persistent infection -begins with acute infection becomes dormant- lack of demonstrable virus. It can be reactivated at any time to be detectable.

Slow infection:
* A type of persistent infection - usually does NOT start with an acute infection
* Prolonged slow incubation of virus –host has no symptoms
* When numbers get high enough, progressive disease occurs

Transformation:
* Activation or introduction of oncogenes (cancer-causing
viruses) causes uncontrolled and uninhibited cell growth.
Transforms regular cell into cancer cell. -HPV

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Specimen Collection
for Virus

A

-collect in 3-4 of symptoms onset after 7 its useless to collect
-take sample from the place the virus is causing the infection. Swab or sterile tub, scrapings, sputum, feces etc
-Sterile samples are BLOOD, FLDS, TISS

Swab tips- cotton, calcium alginate, dacron
Shafts - wood, plastic steel
* For virus investigation use a Dacron or Rayon swabs with a plastic or wire shaft
* Calcium alginate & wood shafts are toxic & interferes with nucleic acid amplification tests.
* Specimens that may be contaminated with normal flora should be placed in a transport media that contains antibiotics

17
Q

Viral Specimen Transport Media

A

-everything BUT flds
- Viral transport media or Universal transport media
-stable for 48 hours
* buffer, protein (albumin, serum or gelatin) & antibiotics (to get rid of contaminating normal flora)
* Phenol red pH indicator -visual gauge of media integrity – should always be light orangy/red

Body fluids:
* sterile plastic container that doesnt break if frozen
* Are not placed in UTM because it might dilute the amount of virus in the sample and limit detection

  • Specimens that can make it to the lab within 72 hours should be refrigerated at 4C or kept on wet ice after collection and while in transit.
  • delays >72 hours frozen at -70C & shipped on dry ice
  • Never freeze at -20C because ice crystals form which are detrimental to virus
  • freezing and thawing destroy the virus
18
Q

4 Main ways to diagnose viral infections in the
lab:

A
  1. Direct detection of virus antigens in clinical specimen
  2. Isolation of virus in cell culture followed by identification techniques
  3. Serological assays to detect Abs to virus
  4. Nucleic acid based detection
19
Q

Direct Specimen Virus
Detection by Microscopy- staining

A

-stain cells or tissue sample
-examine under the microscope for cytopathic effect

(CPE) - distinct characteristic toxic changes in cells or tissue caused by them being infected by a virus
Example:
* Can use PAP stain to visualize HPV or HSV infected cells
* HPV infected cervical cells called koilocytes show CPE: enlarged nucleus, hyperchromasia, irregular
shaped nuclear membrane and nuclear halo
* Koilocytes cells are a precursor to cervical cancer
* HSV infected epithelial cells called a Tzanck cell will show CPE: enlarged multiple nuclei in a molded pattern

20
Q

DFA stain

A
  • Fluorescent stain that contains a monoclonal viral Ab labeled with a fluorescent dye
  • Specimen is put on a slide and fluorescent stain is added & then washed
  • Examined using a fluorescent microscope
  • If you see fluorescence, it means the antigen (virus) is present in the specimen
21
Q

Enzyme Immunoassays:

A
  • detect virus Ag directly from specimens
  • Ab to virus linked to an enzyme – if sample has antigen will bind – add substrate & bound enzyme acts on it to
    cause a color change
  • Color change means the sample had the virus in it
22
Q

Nucleic Acid Detection:

A
  • amplification of viral DNA or RNA to detect them in a sample

Advantages: Faster results, qPCR lets you quantitate amount of virus in sample, multiplexing allows for testing for multiple viruses simultaneously

Disadvantages: Can’t tell if virus is active or not, expensive

23
Q

SEROLOGY

A
  • Test pt for virus Ab’s (& Ag
  • test for presence of IgM, IgG or Ag
  • use paired samples from acute & convalescent stages

Recent or acute infection indicated by:
* Presence of IgM only
* Or a 4 -fold increase in levels of IgG between acute & convalescent sample

Secondary or Past infection or immunity indicated by:
* Presence of only IgG
* Same amount of IgG in both acute & convalescent samples

Chronic infection indicated by:
* Presence of IgG + the viral antigen in patient sample

Serological Methods: Neutralizing Ab, Compliment Fixation, Hemagglutination inhibition, ELIA, Chemiluminescence, Lateral Flow

24
Q

Elisa

A

the wells are coated with the AG of interest, add the pt serum and the AG specific IgG will bind to AG in well forming AG-AB complex.
Anti- human IgG is added to bind to the AB-AG complex. The Anti human is tagged with a enzyme that changes color with positive reaction . The intensity of color depends on the amount of AB-AG complexes

25
Q

Virus Isolation – Cell
Culture

A

-culturing cells and examining for CPE after growth is the gold standard

passaging - when cells used for culturing are kept alive by being removed with trypsin, diluting them and putting into a new container

There are three cell lines - Primary , finite or continuous

26
Q

Primary cells

A

Example: Primary monkey kidney (PMK)

*tissue directly from animal
* Are closest in function & morphology to the tissue the cells are taken from – heterogenous population
* must be passaged to keep alive - limited life span
* once passaged theyre not considered primary cells
* Now become a cell line -either finite or continuous

27
Q

Finite cell lines:

A
  • divide only a limited number of times,
  • Are slower growing, form a monolayer
  • Example: African Green Monkey fibroblasts
28
Q

Continuous cell lines:

A
  • divide indefinitely – immortal
  • spontaneously occur or you can transform cells into immortal cells by using viral oncogenes or by chemically treating them.
  • Or obtain these cells right from cancerous tissue
  • Divide rapidly & can form either a monolayer or survive suspended in media
  • HELa cells are an example of a continuous cell like
29
Q

Mixed cell lines:

A
  • Engineered cell lines that contain two different cell types susceptible to a number of viruses like those that cause respiratory and enteric infections
  • Decreases the number of cell lines to maintain and culture vials to read

the lab decides on what cell line to use based on needs, availability and cost

30
Q

CPE in Cell Culture

A
  • Virus causes characteristic and visible cytopathic or toxic effects to the cells they are grown on
  • Cell monolayer examined daily using inverted microscope For CPE specific to each virus
  • Provides presumptive ID of virus

Types of CPE:
* Rounding
* Detachment (plaques)
* Clumping
* Ballooning (Giant cell)
* Fusion (syncytium)
* Inclusion body formation

31
Q

Rapid cell culture- Shell vials

A
  • Cells grown on a round coverslip in a small flat bottom tube with screw cap or flat bottom microtitre plates
  • Inoculate with specimen and centrifuge at low speed to promote vial adsorption and infection of monolayer
  • Mild cell trauma from centrifugation mitigates virus entry into the cell
  • Incubate 24-48 hrs Or up to 5 days for some viruses
    -stain with anti viral fluorescent monoclonal AB
32
Q

Confirmation of Virus from Traditional
Culture/Shell Vial Culture

A

Immunofluorescence is used after culture:
1. To confirm presumptive ID of a virus based cells showing specific CPE
2. to detect a virus after inoculation and incubation of a shell vial

  • Cells with CPE are scraped from the monolayer or cells from the shell vial coverslip are scraped onto a glass slide
  • First do a screen immunofluorescent test: Add reagent with pooled Ab- has Ab’s to suspected viruses labeled with a fluorescent dye
  • Positive fluorescence =one of those viruses is present
  • then confirmatory immunofluorescent test: Add cells to each of 8 wells on a slide -add monoclonal Ab to specific virus to each

Micro (15 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions