Calicivirus Flashcards
- What are Caliciviridae?
- What group of the Baltimore classification system do Caliciviridae belong to?
- Non-enveloped viruses w/ icosahedral symmetry.
38-40nm diameter.
Capsomers are 90 dimers of a single protein arranged in rings on the faces, w/ 32 characteristic cup shaped depressions. - Group 4 (+ sense RNA genome – replicates by generating -sense copy of itself, which can then be used to make more +sense RNA genomes).
Variety in caliciviridae genera.
Closely related genome structures but are genetically and antigenically highly diverse and infect a wide range of mammalian host spp.
What spp. can be affected by calicivirus?
Rabbits, hares (lagovirus).
Pigs, Mink, dogs, sea lions, bats (sapovirus).
Cows (nebovirus).
Rhesus Macaque (Recovirus).
Pigs, cattle, marine mammals, cats, rodents, dogs, bats (norovirus).
Cats, dogs (vesivirus).
Calicivirus genome organisation.
- Linear, +sense RNA genome.
- Viral RNA is infectious and serves as both genome and viral messenger RNA.
- Non-structural (NS1-7) and structural proteins (VP1 and VP2) are encoded by different open reading frames (ORFs).
- The 5’ terminus is linked covalently to a viral protein genome-linked (VPg) protein.
- The 3’ terminus has a poly (A) tract (protective).
- 6-8.5kb long.
Calicivirus genome replication.
+ strand genomes can be directly translated into proteins by host cell ribosomes.
RdRp encoded by viral NS7.
Genome replicated in 2 steps:
- 1) +strand first copied into a full length negative strand.
- 2) negative strand then copied in a full length +strand.
What protective feature is on the 5’ end of the +strand viral RNA?
Protein VPg.
It is covalently attached to the 5’ end.
- It protects the 5’ end of the viral RNA from cellular exonucleases that act in 5’ – 3’ manner.
- Acts as a primer during -ve strand RNA synthesis.
VPg interacts with RdRp = primer dependent replication.
Infection and replication of Calicivirus.
- Attachment of virus to cell surface using carbohydrate attachment factors.
- Entry is dependent on Clathrin-mediated endocytosis.
- Uncoating and RNA release – acidification of the endosome is essential for the uncoating of FCV and the release of the viral RNA into the host cell cytoplasm before replication can ensue.
- The VPg linked to the genome interacts w/ the cellular translation machinery complex and the 40S ribosomal subunit.
- Polypeptide generated and cleaved into lots of individual proteins.
- Then replication of the genome – RdRp making copy of genome. (+sense copied into neg sense).
- Neg sense genome now used as template to make +sense viral genome w/ another RdRp in cytoplasm.
– binds to free VPg also to form complex to allow replication to occur. - W/ viral genomes and viral proteins, viral particles can form which can exit cell.
- What does JAM-A stand for?
- What is it?
- In what part of the cytoplasm does the replication of calicivirus occur?
- Junction Associated Molecule-A.
- A receptor at the cell junctions that feline calicivirus binds to via the viral capsid protein VP1.
- On membranous vesicles at ER and golgi.
What happens when VP1 and VP2 are expressed together?
Self aggregation = Viral particles are formed w/ distinctive cup-shaped depressions.
Is calicivirus cytopathic?
Yes, it causes the death of the cell (lysis) that it is infecting.
What is a plaque assay?
Grow a lawn of susceptible cells on a plate.
Stain the cells (e.g. Crystal Violet).
Add sample (e.g. nasal, buccal etc) to a media.
Dilute mixture of sample and media several times.
Add medias of different dilutions to different plates.
Look at where the viral cytopathic effect is happening.
Count infectious units (areas where stain gone).
Use dilution factor and number of infectious units to determine number of infectious viruses present.
- What does feline calicivirus cause?
- Clinical presentation of feline calicivirus?
- Major cause of upper respiratory disease in domestic and wild cats. Most cats are exposed by 1yr old.
- Gingivitis, nasal discharge, febrile lameness, nasal ulcers, oral ulcers.
How is feline calicivirus transmitted?
Natural transmission mainly by fomites, direct cat-cat contact, and occasionally by aerosol over short distances.
Can also be passively carried to susceptible cats by human handlers.
Large cat populations – ctrl relies on good management procedures.
Clinical and pathological features?
- Infection starts in oropharynx and extends to URT and eyes.
- Initial short incubation period (2-5 days).
- Fever.
- Mild rhinitis.
- Sneezing.
- Nasal discharge.
- Conjunctivitis.
- Palatine ulcerations.
- bronchopneumonia in some cases.
- foot pad lesions.
What does VSD stand for and how is this relevant to calicivirus?
Virulent systemic disease.
Can get strains of feline calicivirus that cause systemic disease.
Started in late 1990s and leads to death or euthanasia in 50% of infected cats.
Cats show varying degrees of pyrexia, cutaneous oedema, ulcerative dermatitis, anorexia, jaundice, severe resp. symptoms, pancreatitis, hepatic necrosis, multi-organ failure and Disseminated Intravascular Coagulation (DIC).
