Virology - Calicivirus, coronavirus, reovirus, flavivirus Flashcards
Calicivirus Coronavirus Reovirus Flavivirus
Is calicivirus enveloped?
No
What kind of symmetry does calicivirus nucleocapsid have?
Icosohedral
How many dimers does calicivirus have?
90
What kind of classification of virus is calicivirus?
Positive sense single stranded RNA virus - group 4 of Baltimore classification system
What is an example of a calicivirus?
Norovirus
What does calicivirus mainly cause?
Gastroenteritis - vomiting, diarrhoea
What species does calicivirus affect?
Most species
What are the structural proteins initials?
VP
How many non structural and structural capsid proteins does calicivirus have?
NS - 7
VP - 2
What is the important protein called on the calicivirus and where is it located?
VPg
Covalently bonded on the 5 prime end (5’)
What is found at the 3’ end and what is it for?
Poly A tail
Increase the stability of the RNA
Help transport newly synthesised RNA out of the nucleus into the cytoplasm
What is a strand of positive sense RNA the equivalent to? What does this mean?
mRNA
It is infectious on its own
How does the calicivirus replicate?
It converts its positive sense RNA into negative sense RNA
This then acts as a template for millions of copies of positive sense RNA to be made
What does RdRp stand for and what is it for?
RNA dependent RNA polymerase
Needs RNA to build RNA
Is used to replicate the viral genome
What is RdRp encoded by?
Viral NS7
What does the 5’ cap VPg do?
Protects the 5’ end of the viral RNA from cellular exonucleases
Also acts as a primer during negative strand RNA synthesis
What are the steps of calicivirus infection and replication?
Attachment - cell receptors
Entry - endocytosis
Uncoating and RNA release - escapes the endosome
Translation - RNA attaches to ribosomes and produces RdRp viral protein
RNA replication - RdRp binds to viral genome and replicates it
Assembly - RNA is encapsidated
What receptors does feline calicivirus bind to?
Sialic acid
Junction Associated Molecule-A (JAM-A)
What does calicivirus use to bind to receptors?
VP1
Where does calicivirus replication occur?
In the ER and golgi in membranous vesicles
What is self assembly?
When viral proteins find it more energetically favourable to interact with each other to remain alone
What does calicivirus have on its surface?
32 cup shaped depressions
What does calicivirus do to the cells?
Causes cell lysis/death - cytopathic
Why does calicivirus cause cell death?
Has to exit the cells but it is not enveloped (doesnt bud from the surface of the cell) so cant get out otherwise
What disease does calicivirus cause in cats?
Feline calicivirus (FCV) infection - cat flu
What are the symptoms of feline calicivirus?
Acute oral and upper respiratory system disease Sneezing Palatine ulcerations Fever Nasal discharge etc.
How is feline calicivirus transmitted?
Fomites, direct contact and aerosol over short distances
What is the worse strain of FCV called? What does it cause?
FCV-associated virulent systemic disease
Multiple organ failure
Disseminated intravascular coagulation
Do cats recover from calicivirus?
Most do but some remain as carriers or have persistent infection in some adult cats
How does calicivirus evade the immune system in persistent infection?
Antigenic drift
How is calicivirus diagnosed?
Swabs from nose and oropharynx
Identification using PCR
Can you vaccinate against calicivirus? How?
Yes - intranasal
What antibody is used in the calicivirus vaccine?
IgG
What disease does calicivirus cause in rabbits?
Rabbit haemorrhagic disease
What is the mortality rate of rabbit haemorrhagic disease?
80% - high
How is rabbit haemorrhagic disease transmitted?
Faecal-oral route
Biting insects
Flies
Fomites
What are the symptoms/pathology of rabbit haemorrhagic disease?
Nasal haemorrhage
Necrosis of the liver
Disseminated intravascular coagulation
How is rabbit haemorrhagic disease diagnosed?
Immunofluorescence
PCR - detect viral genome
ELISA - detect viral proteins
Electron microscopy
Is there a vaccine for rabbit haemorrhagic disease?
Yes
What order of viruses is coronavirus in?
Nidovirales
What viral classification are nidovirales?
Positive sense single stranded RNA viruses - group 4 of Baltimore classification system
What does polycistronic RNA genome mean?
The separate proteins that are encoded are found on a single molecule of mRNA
What family is coronavirus in?
Coronaveridae
What genus are in the family coronaveridae?
Coronavirus
Torovirus
What is the genus coronavirus split into?
Alpha, beta and gamma coronaviruses
What do coronaviruses look like?
Surface projections forming a spherical halo made of club shaped surface spike proteins
Does coronavirus have an envelope?
Yes
What symmetry does the coronavirus nucleocapsid have?
Helical - unusual as most positive sense RNA viruses have icosahedral symmetry
What shape does the torovirus have?
Crescent shape
What shape do bafinivirus and ronivirus have? (In the coronaveridae family)
Rod
What is the coronavirus spike structure?
Trimer
Three receptor binding S1 domains
Three S2 domains which anchor the spike into the envelope
How does coronavirus enter cells?
Receptor binding domain on the end of the spike protein attaches to a host cell receptor
This causes endocytosis
Where do coronaviruses replicate?
In the cytoplasm
What does translation of the positive strand genomic material produce?
A large polyprotein which can be broken down into viral proteins such as RdRp
What do viruses assemble in?
Intracellular vesicles
What is a syncytia?
A large multinucleated cell formed from the fusion of lots of different cells
What causes syncytia to occur?
Spike proteins being expressed on the surface of infected cells attach to receptors on neighbouring uninfected cells and fuse them together
How do coronaviruses exit cells?
Budding from the ER into vesicles and then exocytosis
Because they have an envelope
What is the structure of the coronavirus genome?
Nonsegmented - all genes encoded on a single strand of the genome
Largest genome
What do the open reading frames encode?
The replication machinery
What do the nested set of genes on the 3’ end of the genome encode?
Viral structural proteins
WHat is subgenomic RNA?
The genome is truncated - a portion/fragment of the original size
What causes subgenomic RNA?
The RNA polymerase gets bounced off the genome at transcription-regulatory sequences (TRS)
When it rejoins the genome, it skips a bit
What is the process of producing subgenomic RNA called?
Discontinuous transcription
What are the different lengths of RNA that are produced called?
Nested RNA
What is the main disease in pigs that is produced by coronavirus?
Porcine transmissible gastroenteritis
What are the symptoms of porcine transmissible gastroenteritis?
Watery diarrhoea
Vomiting
What is the route of infection of porcine transmissible gastroenteritis?
Ingestion via faecal-oral route
What age of pigs does this affect?
Neonates - mortality
Does cause morbidity in older pigs though
What receptor does porcine transmissible gastroenteritis virus attach to?
Animopeptidase-N (APN) - on epithelial cells of intestinal villi
What part of the intestinal villi is affected in infection by porcine transmissible gastroenteritis?
Crypts
Also infect paneth cells in crypts
What do paneth cells do?
Specialised secretory cells
Produce antimicrobial peptides and immunomodulatory proteins
Regulates composition of gut flora
What does infection with porcine transmissible gastroenteritis ultimately cause?
Stops epithelial escalator Affects villi integrity - blunts them Villi slough off Loss of balance of the gut flora Loss of fluid absorption Cant digest milk
How is porcine transmissible gastroenteritis diagnosed?
Histological staining of the intestines
ELISA on faeces
PCR
How are piglets protected against porcine transmissible gastroenteritis?
Maternal IgA antibodies via colostrum
What are the two types of feline coronavirus?
Feline infections peritonitis virus (FIPV)
Feline enteric coronavirus (FECV)
How is feline coronavirus transmitted?
Faecal-oral route
What does FECV infect?
Gastrointestinal epithelial cells only - causing enteritis
What are the clinical signs of FECV?
Few outward signs
Usually chronic
May be brief bouts of diarrhoea
What is the outcome of FIP?
Progressive disease that is almost always fatal
What is the timeframe of FIP?
8-9 days
How do cats get FIP?
FECV virus mutates in 10% of cats and infects WBCs - monocytes and macrophages
This spreads the virus throughout the body causing big inflammatory reaction in abdomen, kidney and brain
What is antibody dependent enhancement?
Where virus infects macrophages better in the presence of antibodies that are against the spike protein
How do you diagnose FECV and FIP?
Histological examination - only definitive one for FIP
ELISA doesnt distinguish between FECV and FIP
PCR
Can you vaccinate against FIP?
Yes - intranasal
Live mutant strain of the virus
Designed to prevent antibody dependent enhancement
What kind of classification of virus is reovirus?
Double stranded RNA viruses - group 3 in the Baltimore classification system
What viruses are included in the reoveridae family?
All animal viruses with multisegmented double stranded RNA genomes
What kind of symmetry does reovirus nucleocapsid have?
Icosahedral
Are reoviruses enveloped?
No
What is the structure of the reovirus capsid?
Triple layered
What is the structure of the genome of reoviruses?
No poly A tail (does still have a 5’ cap)
Segmented - 9-12 segments
Double stranded
What are the two ways that reovirus alters its genome?
Genetic shift and genetic drift
What does the segments allow reovirus to do?
Genetic shift - via genetic reassortment of the segments
What is genetic shift in reoviruses?
Where they swap segments of their genome with other reoviruses that are coinfecting the same cell forming a recombinant virus
This is a sudden change/mutation.
What is genetic drift?
When mutations occur when the genome is replicating using RdRp
mutations are slowly accumulated over time
How is the reovirus genome replicated?
Negative strand is copied into mRNA by RdRp
These mRNAs are encapsidated and copied to produce negative RNA
The +ve and -ve RNA strands base pair to produce double stranded RNA
Where does reovirus replication occur?
Entirely in the cytoplasm
What does reovirus use to bind to the receptors on host cell?
Sigma1 protein
What receptors does reovirus bind to?
Sialic acid
JAM-A
What extra protein does reovirus use to bind to integrin as a final step to enter the cells?
Lambda1 protein
What are reovirus inclusion bodies called?
Viral factories
Where are viral factories located?
ER vesicles
What do viral inclusion bodies include?
Filaments
Viral proteins
Single and double stranded RNA
Viral particles
What are examples of reovirus?
Rotavirus
Bluetongue virus
What does rotavirus cause?
Watery diarrhoea in young animals (especially intensively farmed)
Looks like white scours
Vomiting
Dehydration
What are rotaviruses divided into and which is the biggest?
Serogroups A-G
A contains the most isolates
How is rotavirus transmitted?
Faecal-oral route
How does rotavirus affect the intestines?
They destroy terminally differentiated enterocytes at the tips of the villi
Shortens the villi so reduces the SA
How does rotavirus cause vomiting and diarrhoea?
NSP4 is released from infected enterocytes
This signals for increased secretion of chloride ions into the intestinal lumen
This causes water to move into the lumen by osmosis
It also stimulates enteric/vagal nerves for intestinal motility and nausea
How do you diagnose rotavirus?
Electron microscopy
ELISA
PCR
What type of vaccine is used for rotavirus and who is it administered to?
Killed virus vaccine
Pregnant animals - raises antibodies (IgA) in colostrum
What is the vector for bluetongue disease?
Culicoides - biting midges
What parts of the body are affected by bluetongue disease?
Initially replicates in the draining regional lymph node
Spreads to organs such as lungs, lymph nodes and spleen
What cells does bluetongue virus replicate in?
Macrophages
Dendritic cells
Vascular endothelium
What cells does bluetongue virus spread in?
All blood cells
What are the clinical signs of bluetongue disease?
Most are asymptomatic
Fever, conjunctivitis, lameness, cyanosis, drooling etc. in varying degrees
What causes death from bluetongue disease?
Pulmonary oedema
How does the virus survive vector free periods?
Overwintering in host lymphocytes - gamma delta T cells
What do inflamed fibroblasts express?
WC1 ligand
What activates T cells to release the bluetongue virus from dormancy?
Co culture of the gamma delta T cells and fibroblasts during inflammation caused by the midge bite
How do you diagnose bluetongue disease?
PCR detecting viral RNA
Difficult to culture
Can you vaccinate against bluetongue disease?
Yes - but only if it is the same serotype as the vaccine
What do you use to vaccinate against multiple serotypes of bluetongue disease?
Polyvalent vaccine
What does flavus mean?
Yellow
Does flavivirus have an envelope? Any features?
Yes - tightly adhered with glycoprotein spikes
What classification of virus is flavivirus?
Single stranded positive sense RNA - group 4 of the Baltimore classification system
What symmetry is flavivirus?
Icosaheral
What is an example of flavivirus in humans?
Zika virus
What are the two main genera of flaviviridae?
Flavivirus
Pestivirus
What vectors spread flavivirus?
Mosquitos and ticks
What cells does flavivirus infect initially?
Keratinocytes and skin dendritic cells in the epidermis
Where in the body does flavivirus replication occur?
Lymphoid organs
Where in the body does flavivirus affect?
Central nervous system - neuroinvasive and neurovirulent
What do the glycoprotein spikes on the flavivirus bind to on target cells to cause endocytosis?
Lectin receptors - DC-SIGN and DC-SIGNR
What do flaviviruses have on their 5’ and 3’ ends of the genome?
5’ - capped
3’ no poly adenylated/poly A tail
What causes the varying lengths of viral genomic RNA (sfRNA) in flaviviruses?
A host enzyme called XRN1 digests it
What does sfRNA stand for?
Small fragment RNA
How does the sfRNA help the flaviviruses?
It makes it more infectious and replicates better
It also stops the immune response
Where does virion assembly occur?
On the membranes of the endoplasmic reticulum
How do immature virions mature?
Conformational change occurs as the virion is transported from the ER to the acidic pH in the golgi
What is cleaved on the virion to make flavivirus infectious? What is produced?
prM protein is cleaved to make M protein
What is the enzyme that cleaves the prM to make the M protein in flavivirus maturation?
Furin
How does flavivirus exit the cell?
Exocytosis and lysis
What are examples of flaviviruses?
Louping ill virus
Bovine viral diarrhoea virus (BVD)
What is louping ill virus spread by?
Ticks - ixodes ricinus
Uses the tick grouse cycle
What part of the body does louping ill virus affect?
CNS - meningoencephalitis
What animal does louping ill virus affect?
Sheep
Other animals can be carriers though
What symptoms does louping ill virus cause?
Two phases
1 - flu like symptoms
2 - more severe, fever and neuro effects
How do you diagnose louping ill virus?
Histology of CNS material
Detection of IgM through ELISA
PCR
Culture
How are animals vaccinated against louping ill virus?
Inactivated virus
Passive immunity from colostrum
What is a diagnostic marker for louping ill virus?
Haemagglutination inhibition - when there is no agglutination of virus and RBCs if they are mixed in serum
What genus is bovine viral diarrhoea (BVD) virus in?
Pestivirus
What is persistant infection by BVD called?
Mucosal disease
What is BVD made up of?
Two major genotypes
Two distinct biotypes in each genotype
What are the different types of biotypes of BVD?
Cytopathic and non-cytopathic (persistant infection)
Which is the most common biotype of BVD?
Biotype 1
What does conversion of biotype 1 to cytopathic form cause in BVD?
Typical mucosal disease
What does conversion of biotype 2 to cytopathic form cause in BVD?
Thrombocytopenia and haemorrhagic disease
Less common
What causes conversion of biotypes to cytopathic strains in BVD?
Massive changes to the viral genome caused by mutations and recombination events
What are the symptoms of BVD?
Mostly subclinical - morbidity rather than mortality Fever Diarrhoea Inappetence Depression
When in gestation does transplacental infection of BVD cause persistent infection?
Between 90-120 days of gestation after foetal immune system develops
Infection before this causes foetal death
When can a persistent infection of BVD turn into a cytopathic disease?
Between 6 months and 2 years
What is the mortality rate of mucosal disease?
100%
What does the cytopathic biotype of BVD have a tropism for?
Gut lymphoid tissue
How do you diagnose BVD?
Look at herd repro records - abortion etc.
Tissue culture - immunofluorescence
PCR
ELISA
How do we control BVD?
Remove persistently infected animals
Inactivated vaccines - reduces clinical disease but not foetal infections
