Virology Exam 1

1. encounter frequently and some cause devestating disease

2. high economic impact diseases

3. cause zoonotic diseases

4. induce cancers (oncogenic)

5. newly emerging viral diseases

6. they are toold for cell biology, gene therapy, vaccines

6 important ways viruses impact domestic animals, humans, and science

1. rabies

2. influenza

3. MERS/ SARS

4. Ebola

5. West Nile

5 examples of zoonotic viruses

naked virus, have indestructable protein shells

which is harder to target: enveloped or naked viruses

host cells because they cannot produce their own energy or proteins (obligate intracellular pathogens)

what do viruses require to survive

very very small though there are ones bigger than small bacteria

what is the size of viruses

1. efficient transmission

2. they are very prone to mutations

3. sucessfully evade host defenses

4. there is limited treatment avialability

5. many species can be infected

5 reasons viruses are so formidable

1. gorw to high titers and shed in large amounts

2. very stable in the environment (naked is best)

3. use a wide variety of transmission modes

3 ways viruses are so good at transmission

more in RNA viruses because have DNA and RNA polymerases to make mistakes

do RNA or DNA viruses have more mutations and why

1. latency (delay between cause and affect)

2. antigenic variation

3. immune supression

3 ways viruses evade host defenses

1. antiboitics will not work unless secondary bacterial infections

why is there limited treatment avialability for viruses

1. primary infection-reinfection

2. wildlife

3. vectors

4. persistently infected hosts

5. environment

5 sources of viruses

1. use bate vaccines (raccons and rabies)

2. cull wildlife to stop zoonotic transmission

2 forms of dealing with viruses from wildlife

1. PPE - big spray, etc.

2. remove standing water/ breeding locations for vectors

2 forms of dealing with viruses from vectors

herpies virus - finds a place to hide and can persistantly infect the population in times of immunocompromisation

describe source of virus: persistently infected hosts

culling or isolation

solution for virus sourced from perisistenly infected host

1. clean environment

2. keep contaiminated environment seperate

2 ways of dealing with viruses sourced from environment

transient infection that comes and goes

describe primary infection-reinfection source of virus

vaccinations

primary way to address primary infection-reinfection source of virus

1. vaccination

2. passive immunity

3. quarentine

4. cull

4 solutions to overall viruses

yes, 8% of our genome is endogenous (interlay originating) retrovirus, also JSRV retrovirus makes enveloped protein needed for placental development in sheep

are some viruses good

used to deal with bacteria in the face of antimicrobial resistance

viruses in treatment

virion

name for intact, complete, physical infectious virus particle

huge variety, DNA, RNA, ds, ss, linear, circular, single molecule, segments, haploid (retroviruses = diploid)

characteristics of viral genomes

can be positive, negative, or ambisense (both)

positive single sense mRNA is what can be red by ribosome to make proteins so viruses need special protein to make the genetic material into positive polaric mRNA

significance of polarity in viral genomes

make contact with cell surface and initiate virus entery into cell

function of capsid or envelope glycoproteins

viral genome

what encodes capsid proteins

1. icosahedral (common)

2. helical

2 forms of capsid symmetry

icosahedral

name capsid structure

rabies

example of virus with capsid in helical form

most efficient way in forming the shell: minimal energy, very stable

why is icosahedral symmetry most common in virus capsids

more proteins

what makes more complex viron

adenovirus has no envelope and herpies has an envelope

difference between edenovirus and herpes virus

rod shaped viruses (bullet)

what types of viruses have helical capsid symmetry

self assemple with viral genome forming spiral within the capsid

how are helical capsids formed

enveloped and RNA viruses

all animal viruses with helical capsid symmetry are ___

1. protect genome

2. delivery viral genome

2 main capsid functions

1. bind to cell membrane

2. promote uncoating og genome to give to polymerase

3. after duplication, re-capsulate genomes

4. facilitate exit of cell through rupture of budding

how capsid facilitates delivery of viral genome

1. basis for serodiagnostic tests

2. target for vaccine development

3. cause robust amune response - outside of virus is what the body responds to and makes Ab to

why: because capsid proteins are highly conserved so they have very slow change over time

3 clinical significance of capsid and why

does not kill the virus, just stops it from taking action

define neutralizing Ab

antibodies cover the capsid/envelope proteins which bind to cell receptors so they can no longer unlock the cell

how do neutralizing Ab work on viruses

lipid bilayer(from host) and glycoporteins(from virus)

what makes up the virion envelope

by budding out of some host cell membrane - usually the plasma membrane and taking the lipid bilayer with it

how does the virion aquire the lipid bilayer of the envelope

1. bind to host cell receptors (host specificity)

2. fuse to cell membrane for entry (enveloped can directly fuse lipid bilayer to cell lipid bylayer)

3. facilitate exit from host cells

4. uncoat nucleaic acids to allow polymerase access

4 functions of envelope and glycoproteins

protective and neutralizing agents

2 unique functions to viral glycoproteins

1. matrix - inner layer of envelope (rigidity)

2. nucleocapsid - additional layer surrounding genome

3. tegument - between capsid and envelope of herpesviruses

3 other structural proteins fond on virions

1. polymerase - biosynthesis

2. regulatory/accessory proteins - alter intracellular environment for biosynthesis

3. non viral (host) proteins

3 non structural protein components of virions

no (except non enveloped viruses) they are very suceptable to physical and chemical agents

are viruses very stable

temperature

what is a big environmental factor for a virion stability

1. type of viral genome

2. virion structure

3. strategy of virus replication

3 factors used for classification of virus

family -viridae

subfamily -virinae

genus -virus

species

levels of taxonomy

same species of virus, different viral proteins and nucleic acid

what is a serotype

different presentation to host, so Ab for one serotype will not work on a different serotype

- need neutralizing antibodies to coat the virus outside

significance of different seroutypes and immune response

same serotype, other biological difference - genome

what is a strain

sample of virus from specific source

what is a virus isolate

- type of transmission

- system affected

- type of disease causes

3 things viruses based on epidemiology classification is based on

respiratory viruses

enteric viruses

arboviruses (arthropod borne)

3 examples of viruses grouped based on epidemiology

- type of genome

- enveloped, non enveloped

- segmented genome or not

- type of disease/transmission/control

4 taxonomic focus for viruses in this course

latency- for life, virus hides and waits for opportunity

important reature of retrovirus and herpesviridae families

2-3

the appropriate virus-cell interaction for virus attachment is

1. cell death: release viruses

2. persistence, productive: slow release of virus without cell death

3. persistence, non-productive (latency): present virus without replication but genes are still there

4. neoplasia: with or without virus production (sometimes just from virus damage)

4 diseases due to virus replication in host cells

unique period in viruses where there is a break down and exposure of nucleic acids to be copied and repachaged

- no infectious virus detectable

- uncoating

describe eclipse period

shorter eclipse period and higher burst size = more mean virus

relationship of viral growth curve and strength of virus

1. virus production occurs in step wise fashion

2. replicating entity is a virus (eclipse phase)

3. how fast the virus replicates (length of eclipse phase)

4. how many progeny viral particles are produced per cell (burse size)

4 factors the viral growth curve tells us

attachment

the goal of vaccination is to interrupt the viral replication cycle at what stage?

virus-receptor interations

what is the key point of virus vulnerability

viral attachment protein (ligand) on the virus connect with virus receptor on cell

how does viral attachment occur

different virus receptors on host cells

why do viruses impact only specific organs sometimes

cells without appropriate receptors

what would make a cell not susceptible to infection by viruse

expansion of tissue preference by virus, host range, and emerging disease

what does changing receptor usage result in

started as feline panleukopenia and then capsid proteins evolved to work for dogs and made parvo and then evolved again to be in dogs and cats

descirbe progression of canine parvovirus

went from racing horses and then had change in viral ligand to enter racing dogs

describe significance of canine influenze H3N8

receptor mediated endocytosis (naked proteins do not fuse)

main form of entry for enveloped virus and naked

1. membrane puncture

2. direct penetration: perforation, lysis

how do naked viruses specifically penetrate membranes

viral fusion proteins in virus envelope

what do enveloped proetins used to penetrate membrane with fusion

they can be the same protein with different domains or different proteins

fusion protein: all enterance into membrane

attachment protein: allow connection

difference between attachment and fusion proteins

have hydrophobic domains (fusion peptides) to be inserted into the membrane

how do fusion proteins work

stimulus causes conformational change to expose the fusion peptide

how are fusion proteins moved from inactive to active

inactive form have hemagglutinin (fusion protein) hidden but multiple triggers lead to conformational change to expose it

describe influenza fusion protein inactive to active change

the absence of correct cellular protease dictates development of disease because it is an activator of fusion proteins

role of protease in viral penetration

- tissue tropism

- host range

- virulence

what do fusion proteins determine (3)

- host immune defences

- antiviral drugs

what are fusion proteins a good target for

syncytial cells because fusion with neighboring cells into one big cell

what can fusion proteins cause to form with surrounding cells

low PAI has low mortality where HPAI has high mortility and the only difference is the proteolytic cleavage site

- LPAI has cleavage site that only few proteases (tripsin) can work on in the respiratory and intestinal organs

-HPAI cleavage site can be cut by most proteases in all sites

explain the difference between low path avian influeza and high path avian influenza and why

endocytic vessicle, cannot leave vessicle unless cleaved

where does protease cleaving of fusion proteins occur

with penentration or shortly after with cellular enzymes and lower pH

when does uncoating occur

1. genome

2. capsid

3. envelope glycoproteins

what 3 things must be formed in biosynthesis

DNA dependent RNA polymerase

what reads DNA and makes mRNA

1. synthesize mRNA to make proteins

2. replicate genome to make more to package into virions

2 requirements of virus in biosynthesis

RNA dependent RNA polymerases

what protein do viruses uniquely have that aids in biosynthesis

make mRNA that is recognized by host cells and goes through host cell translation

regardles of how they replicate, how do all viruses end up getting proteins

+mRNA

what type of information do ribosomes read

cellular DNA dependent RNA polymerase

excpetion: Asfar and Pox carry own DNA dependent RNA polymerase

what do most DNA viruses use to make RNA

hosts DNA dependent DAn polymerase

exception: herpesvirus uses their own DNA polymerase (anti viral target)

how do DNA viruses replicate genome

synthesize different classes of viral genes at sequential times

describe how DNA viruses regulate gene expresion temporally

1. virus does not have to compete with host cell for gene expression because turn off those genes

2. delay expression of highly antigenic structural proteins

2 advantages of temporal regulation of DNA virus gene expression

rapdily dividing cells

ex. papalloma virus upregulates gene expression tog et more cell division

what type of cell do viruses want and give example

only RNA viruses

what organisms have RNA in genetic matierial

1. strandedness

2. segmentation

3. polarity

3 characteristics of viral RNA genomes

virus encoded enzymes: RNA dependent RNA polymerase encoded by the virus

what do RNA viruses use for replication

RNA dependent DNA polymerase/ Reverse Transcriptase

- to go from RNA to DNA and then to +mRNA to protein

- or go RNA to DNA intermediate and then copy into RNA with cellular RNA polymerase

what must the retroviridae carry for genome replication and protein synthesis