Microbio- viriology Flashcards
What did Pasteur develop?
vaccine against rabies
What did Chamberland develop?
a filter to remove bacteria from water
What did Ivanoski discover?
there was filterable infectious agents
What did Beikerinck discover and what were Loeffler & Frosh the first to prove?
Beikerinck discovered that the agent multiplied only in cells
Loeffler & Frosch were the first to prove viral infections in animals
What was Stanley the first to see under a microscope?
the viral structure under EM with tobacco virus
what type of parasite are viruses and what are two characteristics of it?
obligate intracellular
inert outside host cells
hijack and utilize host cellular metabolism to make energy or proteins
what are 6 characteristics of viruses?
small and filterable (pore size 0.2 um) found in almost every ecosystem on earth non-living entities survive hours to days outside host cells shows reduced infectivity with increased time outside host cells don't have standard cellular organelles
define virology
the study of viruses and viral diseases
define virologist
someone who studies viruses
define veterinary virology
the study of viruses in non-human animals
what are 3 reasons why studying veterinary virology is important?
viruses cause high rates of mortality and morbidity in animals
viral diseases in animals cause financial losses to livestock and poultry industries and national and global economy
some viruses are zoonotic
what is the host range of viruses (5) and what is an important fact about host range?
vertebrates, invetrebrates
protists
bacteria, fungi
most viruses are host specific
define bacteriophages and what is an example of the use of bacteriophages?
viruses that infect bacteria
phage therapy to kill bacteria- treatment of wound and skin infections
define onolytic viruses, what can they be used for and what are 6 examples?
viruses that infect and kill cancer cells
oncolysis- stimulation of host anti-tumor immune response
adenovirus, reovirus, measles, vaccinia, Newcastle disease virus, Herpes
what are the 5 components of the virus structure?
nucleic acid capsid capsomere envelope envelope proteins
what is the viral genome made of?
RNA or DNA
what is the capsid and what are 3 characteristics?
protein shell that encases the viral genome most viruses have one capsid (reoviruses have double layered capsid) usually symmetrical (Helical, icosahedral, complex) functions: protection, antigenic sites, attachment
what is the capsomere?
basic subunit protein of the capsid
what is the nucelocapsid?
capsid + viral genome
what is the envelope and what are two functions?
lipid bilayer with embedded (glyco)proteins
facilitates virus entry into host cells
helps virus to adapt fast and evade host immune system
define virion
a coplete virus particle that consists of an RNA or DNA core with a protein coat, sometimes with an envelope
the extracellular infective form a virus
define virus
any aspect of the infectious agent and includes:
the infectious (virion) or inactivated virus particle
viral nucleic acid and protein the infected host cell
define viroid
infectious particle smaller than any known viruses
an agent of plant diseases
particle consists of an extremely small circular RNA molecule, lacks the protein coat
What are the ways to classify viruses? (4)
envelope: naked, enveloped
capsid symmetry: icosahedral, helical, complex
nucleic acid: DNA, RNA, both DNA & RNA
genomic architecture: linear, circular, segmented; ss, ds, ds with regions of ss; sense (+,-,+/-)
define icosahedral capid symmetry
protomers aggregate to form capsomeres which are either hexons or pentons
define helical capsid symmetry and what is the difference when in animals vs plants?
capsomeres and nucleic acid wind together to form a helical or spiral tube
animal= enclosed in a lipoprotein envelope
plants= naked
define complex capsid symmetry, what are two examples and characteristics of them?
virions are composed of several parts, each with separate symmetries and shapes
bacteriophage= icosahedral head and helical tail
pox virus= produces more than DNA and capsid, has additional genes that encode for enzymes
define sense and strandedness for genome architecture, and what is it a reflection of?
sense: polarity of the genome (+ or -)
strandedness: ds or ss
reflection of different replication strategies
what are three possible effects of viruses on infected host cells?
abnormal cell growth
cell damage/death
no apparent changes
what is the result of abnormal cell growth from infected host cells and what are 2 examples?
cancer
Thymic lymphoma in Feline Leukemia Virus
large skin lesions from Papilloma Virus in giraffe
what are 3 results of cell damage/death from infected host cells and what is an example?
lysis= cell bursts open and everything inside the cell spills out- causes severe inflammation
cell membrane alteration
apoptosis= phagocytes eat the material from the killed cell- no inflammation
infectious canine adenovirus induces damage/death of hepatocytes
what are 3 results of no apparent changes of infected host cells and what is an example?
persistent
latent
immuno-suppression
herpes virus
what is an important reservoir host for viruses and why?
bats
important risk in human and animal public health- more than 60 viruses have been detected in bats
what are 4 types of disease transmission and what are examples for each?
horizontal- squirrel pox virus, blue-tongue virus
vertical- canine herpes virus, BVD
cross-species- malignant catarrhal fever: transmitted to cattle from sheep/goats
zoonosis- rabies, SARS, buffalo pox
what are 6 types of routes of transmission?
abiotic environmental factors (wind/water) animal vectors direct contact indirect contact droplets airborne fecal oral
what are the 6 steps of viral replication?
attachment penetration uncoating replication assembly release
what are three characteristics of viral genome?
contains only few genes
genes encode for structural components (capsid proteins)
genes encode for enzymes necessary in the virus life cycle, mainly for nucleic acid synthesis (reverse transcriptase)
what kind of parasites are viruses and what can’t they do?
obligate intracellular
can’t make energy or proteins by themselves
when are proteins & enzymes synthesized and functional and what kind of enzymes are produced by the host cell (4)?
when virus is inside the host cell
enzymes are supplied by the host cell (protein synthesis, ribosomes, tRNA and energy production)
what is the first step of viral replication and what is it the process of?
attachment/adsorption
attachment of the virion to the host cell surface
what type of interaction is involved in the attachment step of replication, what is the interaction between, and what does it determine?
specific interaction
between capsid proteins or envelope spikes and host cell receptors
determines host-specificity and tissue-specificity of viruses
what is the role of receptors?
selectively bind specific substance and mediate its entry or action into the cell
what is a characteristic of animal virus attachment?
attachment sites are distributed all over the viral surface
what is the 2nd step of viral replication and what is it a process of?
penetration/entry
bringing the viral genome to the other side of the host cell’s plasma membrane by entry of a portion of the virion
what two things are penetration/entry dependent on?
energy and temp
what is the host cell classified as if virus can enter the cell?
susceptible to a virus
what are the 3 different mechanisms of penetration/entry?
endocytosis membrane fusion direct penetration (pore or antibody mediated)
what is endocytosis a process of and how it it done, and what type of viruses use this method?
the virus gains entry into the host cell without passing through the cell membrane
active transport in which the virus is engulfed by an energy-using process
enveloped and naked
what is membrane fusion the process of, what is it mediated by (2) and what viruses use this method?
merging (fusion) of the virus envelope with the host cell lipid bilayer membrane
mediated by pH independent or dependent fusion proteins that are anchored on the virus surface
enveloped
what is direct penetration the process of, what is it restricted to and what viruses use this method?
virual genome injection into the host cell’s cytoplasm after initial attachment
restricted to viruses in which only the genome is required for infection (mostly + sense RNA viruses)
naked
what is pore-mediated direct penetration?
creation of pore in host membrane mediated by viral pore-forming peptide associated in viral capsid
what is the 3rd step of viral replication, what is it the process of and what is it mediated by (2)?
uncoating
capsid protein removal and the release of viral genome in the host cell
mediated by cell pH and lysosomal enzymes
how does uncoating affect the infectivity of virions, how do large viruses differ during the uncoating step?
loss of infectivity of virions
large viruses have their own uncoating enzymes
what is the 4th step of viral replication, what is it a process of and what is the flow of genetic info?
replication/synthesis
genomic expression of the viruses, using host cellular machinery to replicate and make functional and structural proteins
flow of genetic info: transcription to translation
what are 5 key enzymes in genetic info flow and what are they involved in?
DNA polymerase= DNA replication (DNA-> DNA)
RNA polymerase= transcription (DNA-> RNA)
Reverse transcriptase= reverse transcription
Ribsomal enzymes= translation (RNA-> protein)
RNA dependent RNA polymerase= RNA replication (RNA-> RNA) - sense RNA
what is essential for viral protein synthesis, what are two stages of protein synthesis and what do they include?
mRNA synthesis
- early protein synthesis= enzyme polymerase, which makes copies of genetic material from progeny viruses
- late protein syntheses= capsid and/or envelope proteins
what do strategies for genomic differ between and what are two types?
differ between taxonomic groups of viruses
Strandness & sense
location of production of mRNA
what are the two locations for production of mRNA, what type of viruses use each, and what are exceptions for each?
nucleus (using host cell’s DNA- dependent RNA polymerase= DNA viruses (except pox virus, uses cytoplasm)
cytoplasm= RNA viruses (except influenza virus- use nucleus and retrovirus- uses reverse transcriptase)
what is the 5th step of viral replication, what is it the process of, what organelle does it involve and where can it take place (3)?
assembly & maturation
packing the viral genome and proteins into new virions following a specific order
Golgi complex
may take place in nucleus, cytoplasm and/or host cell membrane (mostly for enveloped viruses)
what is the 6th step of viral replication, what is it a process of and what are three different mechanisms?
release/shedding
expulsion and release of progeny virions following replication in infected host cells
budding (enveloped), exocytosis, cell lysis (naked)
what is the process of budding in viral replication and what does it create during the process?
pinching off of the new virus from the host cell’s membrane
creates an envelops during the process
what organelle is used in exocytosis, what viruses use this method and how?
goes through Golgi
enveloped= normal
naked= vesicle from Golgi fuses with virion
what is the process of cell lysis during the 6th step of vial replication, what type of viruses require this method and what is another term for this process?
host cell membrane rupture, actively induced by many viruses
bacteriphages require cell lysis to be released from the infected cell
Lytic replication
what are the 5 steps of the life cycle of an animal virus?
adsorption entry: endocytosis biosynthesis of viral components assembly budding
what are the 7 steps of the life cycle of DNA viruses?
virion attaches to host cell
virion enters and its DNA is uncoated
a portion of the DNA is transcribed, producing mRNA that encodes for early viral proteins
DNA is replicated and come viral proteins are made
Late translation, capsid proteins are made
virions mature
virions are released
what is the life cycle of Pox virus?
ds DNA replicates in cytoplasm
large virus, more genes= carry own RNA polymerase
what are the two forms of the life cycle of RNA viruses?
plus sense= direct translation into proteins used in translation
minus sense= transcribe neg to pos sense then translated
what is a term used to describe retroviruses, what does it mean, how are retroviruses characterized and what is their life cycle?
provirus= virus genome that is integrated into the DNA of a host cell
characterized by 2 identical strands of RNA
reverse transcriptase into viral DNA, the new viral DNA is transported into the host cell’s nucleus and integrated as a provirus
can replicate indefinitely and produce many viruses to be released in the host
What are influenza viruses characterized as, where does replication occur and what is the life cycle?
characterized by spiked envelope and segmented genome
replication occurs in the nucleus
attach to target epithelial cell, cell engulfs the virus by endocytosis
viral contents are released and RNA enters the nucleus to be replicated by the viral RNA polymerase into mRNA to make proteins
new viral particles are released into the ECF, the cell is not killed and continues to make new viruses
what is a term used to describe bacteriophages replication, what does it mean and what are two methods of replication?
prophage= virus genome of bacteriophage that is integrated into the DNA of a host cell
Lytic cycle= phage infects cell, phage DNA circularizes separate from host DNA, gets replicated and makes proteins and assembles new virus, which is released during cell lysis
lysogenic cycle= phage infects cell, phage DNA becomes incorporated into host genome. the cell divides and prophage DNA is passed on to daughter cell. under stressful conditions, can turn to lytic cycle
what does the timing of the one-step growth cycle depend on and what are two examples?
depends on virus and host
bacterial viruses= 20-60 min
animal viruses=8-40 h
what are the 4 stages of the virus growth curve and what does the growth look like in each stage?
adsorption & entry= decline
uncoating & replication= steady at 0
maturation: intracellular viruses= exponential growth, extracellular viruses= slightly higher than 0 plateau
release: intracellular= leveling out, extracellular= exponential growth
what is the eclipse period and when does it occur?
infectivity of the virus disappears due to uncoating
during uncoating & replication phase
what is latent period and when does it occur?
replication of viral nuclei and protein
during uncoating & replication to maturation phase
what is the maturation period?
assembly of viral genome and protein into mature virus particles.
if at this time cells are broken, active virus can be detected
define viremia and what are 4 types?
virus spread via the bloodstream
passive, active, primary secondary
define passive viremia and what are 2 examples?
direct inoculation of virus in host’s bloodstream and no replication at site of entry
contaminated syringe, bite of arthropods
define active viremia
viremia following virus replication in host
define primary viremia
spreading into the blood from infected area
define secondary viremia
spreading to other organs/tissues
what are three different courses of infection in host?
acute
latent
persistent
define acute infection in host and what are 3 examples?
rapid onset of disease and symptoms with brief duration
influenza virus, pox virus, enteric viruses
define latent infection in host and what are 3 examples?
virus remains in asymptomatic host cell for long periods
retroviruses, FIP, Feline herpes virus
define persistent infection in host and what are 3 examples?
disease process over a long period, generally fatal
chronic= bovine viral diarrhea virus (BVD)
slowly progressing= lentiviruses, Jaagsiekte Sheep retrovirus
the threshold of virus is required to activate what during the virus spread in host?
adaptive immune response
what are 5 mechanisms of injury for virus spread in host?
inhibition cytopathic effect neoplastic transformation drive host cell to apoptosis non-cytocidal changes (persistent)
what are three types of inhibition in mechanisms of injury?
host cell nucleic acid synthesis
host cell RNA transcription
host cell protein synthesis
what are two cytopathic effects in mechanisms of injury?
toxic viral proteins
interference will cell membrane function
what are 4 reasons to why it is important to diagnose viral infections?
viral disease diagnosis to determine what antiviral chemotherapy is available
screening of blood donors
proper management of diseases
early detection of epidemics
what are the two methods of lab diagnosis and what are examples of each?
direct: virus isolation, genome detection, antigen detection
indirect: serology for IgM and IgG
what are 5 samples that are required for diagnosis of viral infection?
blood sputum/bronchial washes feces cerebrospinal fluid biopsy/necropsy tissues
what are three uses of blood samples in diagnosis of viral infection?
antibodies
virus if the animal is still in viremic stage
virus in blood cells
what type of samples are used in biopsy/necropsy tissue diagnosis?
for culture= fresh
for antigen= may be formalin fixed