Virology Flashcards
What percent of the human genome is retroviral DNA?
8-10%
Do host-adapted viruses cause damage?
No
Describe the difference between positive sense and negative sense strands
Positive sense are ready to encode
Negative sense need to be converted to positive sense to form mRNA
What is the purpose of glycoproteins?
Used to attach to cell surface of host
What is an envelope?
A membrane covering the capsid that comes from the host membrane
What is the most common symmetry?
Icosahedral or helical
What is a capsomere?
A subunit of the capsid that gives the virus its pattern
What two things make up the virion?
Genomic material and capsid
What is the most stable biological morphology?
Isocahedron
What forms the isocahedron?
Viral protein coat or capsid protein
What defines an isocahedron?
20 Equilateral triangles at its faces
What is T equal to in isocahedron?
1
Are most helical viruses enveloped or non-enveloped?
Enveloped - cannot survive in environment
What makes viruses highly adapatable in hosts?
The envelope
Where does transcription and translation occur?
Transcription - nucleus
translation - cytoplasm
What are 6 DNA viruses? (there is a pneumonic)
HHAPPPY Herpes Hepadna Adeno Papova Parvo Pox
Which 3 DNA viruses are naked?
Adeno
Papova
Parvo
(APP)
Which one of those 6 viruses is not icosahedral?
Pox
Which one of those viruses is not dsDNA, but ssDNA?
Parvovirus
What are the 10 steps of replication for DNA viruses?
- Attachment
- Penetration
- Uncoating of virus + transport of genome to replication site
- Early transcription
- Early translation + early proteins
- Viral DNA synthesis
- Late transcription
- Late translation and synthesis of structural proteins
- Assembly
- Release
Which 3 DNA viruses are enveloped?
Herpes, Hepadna, Pox
How does attachment occur?
Via attachment protein on capsid (naked) or envelope attaching to complementary protein on host cell
What can interfere with attachment?
An antibody against spike protein - evolutionary pressure on spike protein to change antigenic nature
What happens if a virus attaches to a rbc, and what can prevent this?
Agglutination
Antibody against spike protein called Haemagglutination-inhibiting antibody
What does penetration involve? (2 options)
Fusion of envelope with PM of cell (mediated by specific proteins) and release of nucleocapsid into cytoplasm
OR engulfement of virus by cell by adsorptive endocytosis before viral genome released
What does uncoating of virus and transport of genome to site of replication involve, where does it occur?
Occurs in cytoplasm but for most DNA viruses happens in nucleus following migration of nucleocapsid through cytoplasm across nuclear membrane
How does herpes virus gain entry to the nucleus?
Carry protein stimulates cell to do mitosis so virus genome can go into nuclei and replicate
Some viruses can only get to nucleus during mitosis
What happens in early transcription, translation and early proteins?
Formation of mRNA from virus DNA, and formation of early viral-coded proteins
What do early viral-coded proteins do?
Enzymes for DNA synthesis
DNA dependent DNA polymerases for example
What enzyme allows the formation of viral mRNA from viral DNA?
DNA-dependent RNA polymerase
Which strand is transcribed?
Template strand
Where do transcriptional events happen and what virus is the exception?
Nucleus
Poxviruses replicate in cytoplasm
Where does mRNA then go to from the nucleus, and what is formed next? then where do those products go?
mRNA goes from nucleus -> cytoplasm where translation of coded proteins occurs to DNA dependent DNA polymerase for example
Coded proteins then go back to nucleus for late transcription
What happens at late transcription?
The viral progeny and immediate early proteins go into the late transcription phase in nucleus for formation of late proteins that form capsomeres and capsid
Where does the primary assembly of herpesvirus occur?
Nucleus
How does release occur?
By autolysis of the cell or by virus induced programmed cell death
What is a prion?
An abnormal form of normal cell protein found in PM of nerve cells
What does prion infection cause?
Spongiform encephalopathy
What 3 adjectives describe prion infections?
Infectious
Heritable
Spontaneous
What are 2 forms of scrapie?
Classical - transmitted between licking bones (not in aus)
Atypical - spontaneous mutation (in aus)
What lesions in the brain do prions cause?
Vacuoles in brain tissue
spongey appearance
What steps for RNA replication are the same as DNA?
1-3
Attachment
Penentration
Uncoating of coat + release of viral genome
Name 4 positive sense RNA viruses
Picornaviridae
Coronaaviridae
Flaviviridae (pestivirus)
Togaviridae
What dont ss rna positive sense viruses need for transcription and translation?
Intravirion enzymes - they are readily transcribable with mRNA that has a methyl cap and poly-A tail
Which type of virus bypassess the nuclei and begins translation right away in the cytoplasm and what does this cause?
Postivie sense RNA
They replicate in the cytoplasm - no nuclear inclusion bodies
How do capsid and enveloped viruses escape the cell?
Capsid - lysis (induction of apoptosis)
Envelope - budding
Some viruses can escape via cell fusion (transmitted by cell to cell contact)
What happens following uncoating of a positive sense RNA virus (5 steps)
Uncoating -> viral RNA translated -> RNA dependent RNA polymerase created -> transcription of mRNA -> viral capsid proteins translated
Where does genome replication occur in +dsRNA virus?
Within capsid - not cytoplasm
Then mRNA template released and translation happens in cytoplasm
What type of virus forms cytoplasmic inclusion bodies?
Positive sense RNA viruses
Name 6 negative sense RNA viruses
Influenza viruses
Always bring polymerase or fail replication
Arenavirus Bunyavirus Paramyxovirus Orthomyxovirus Filovirus Rabdoviruses
What is the first thing negative sense RNA viruses have to do?
Transcribe to positive sense mRNA template by a viral intravirion transcriptase
Once a negative sense virus has coded for +mRNA, what is produced first, and what combines to form progeny virus?
Early viral proteins (RNA polymerase) -> progeny viral (-)sense RNA
Late viral proteins -> structural proteins
Structural proteins + (-) sense RNA assembled to form progeny virus
What is cap snatching and what virus does this?
Viral RNA dependent RNA polymerase cleaves 5’ capped host mRNAs to prime viral RNA synthesis
Influenza A
How do negative sense viruses replicate?
Virus enters by endocytosis and uncoats
viral mRNA transcribed from neg sense genome -> template for translation
Viral proteins accumulate in cytoplasm + associate with viral RNAs to form nucleocapsids
Virions assembled and released from cell
What is one example of a retrovirus?
HIV
How do retroviruses replicate? (4 steps)
- Reverse transcriptase converts viral RNA to ssDNA, then to dsDNA
- dsDNA enters nucleus via integration complex + integrates into cell DNA
- Host cell transcriptase forms early and late phase mRNA, and progeny viral RNA
- Viral proteins and progeny viral RNA combine to form progeny virus
What is canine parvovirus dependent on to replicate in a host?
Dividing crypt cells
What is the incubation for parvo?
3-7d
What can parvo survive in?
pH 3-9
56-80 degrees for 1 hour
What kills parvo?
Formaldehyde and chloramines
Is parvo enveloped or non-enveloped?
Non-enveloped - can survive in environment
What are 4 factors affecting result of viral infection?
NUmber of particles + virulence
Speed of replication and spread to target organs
Degree of cellular damage
Effectiveness of host defence
What are 3 latent infections?
Herpes zoster
Chicken pox
Shingles
Where are localised lesions limited to?
Sites of entry of virus
Skin, respiratory tract, alimentary tract
What is cell tropism and what are 2 examples?
Viruses having affinity for particular tissues
Rabies - neurotropic
BVDV - lymphoid tissues
May have primary, secondary or tertiary phases of replication in other organs
What is an immunopathologic disease?
Antibodies or lymphocytes aggravate viral infections by contributing to destruction
Equine infectious anaemia
What happens the second time of infection with dengue haemorrhagic fever?
Cytokine storm
Antibody dependent enhancement of viral infection - helps virus bind to Fc receptors on monocyte
What is a self-associated molecular pattern?
A “dont eat me” pattern the virus makes to protect against phagocytosis
BVDV E2 protein - allows infected cells to be recognised as self
What are 3 examples of slow infections?
Rabies
Caprine arthritis encephalitis virus
Feline leukaemia
These are all retroviruses
What is rabies, what does it do and how many types are there?
Enveloped retrovirus transmitted by bites
follows retrograde nerve sheaths to CNS inside sensory axons - long incubation period
11 types of rabies - we dont have classical type
What does canine arthritis encephalitis virus cause?
PI in monocyte lineage
monocytes carry genome, replicate after they leave circulation and mature into macrophages
Replication in mammary gland and lung
What 3 viruses cause proliferative lesions and what do they attack?
Papillomavirus
Poxvirus
Herpesvirus
Target G0/G1 or G2/M checkpoints
What causes viral induced neoplasia?
Papillomaviruses
Retroviruses
Herpesviruses
Cervical cancer
What do papillomaviruses cause?
No cell death, inflammation or viremia
Supress type I interferon to bypass immune system
How to papilloma viruses infect?
Get to BM in skin
Basal cells produce virus + replicate in low concentration
Avoid recognition
Produce viral protein e6 (activate p53 gene) and e7 to cause uncontrolled replication
What are 5 factors affecting transfer and persistence of virus infections?
Resistence to environment Mode of transmission Mutations Multiple hosts Persistent Infection
What are 3 characteristics of a non-enveloped virus?
More resistant to environment
Transmission less dependent on close contact
Smaller populations needed to maintain infection
what are 3 characteristics of enveloped virus?
Inactivated outside animal host
Survival depends on close contact
Transmission best in density
How does west nile virus spread?
Mosquito vectors
How does akabane virus spread?
Culicoides species
potent teratogen in cattle, sheep and goats
Causes target areas to be neuron deficient
When does akabane virus cause lesions?
<70d -> resorption or normal calf
76-104d - absence of cerebral hemispheres
103-174d - loss of ventral horn neurons
Perinatal - encephalomyelitis
How does antigenic shift occur?
Poymerases make mistakes in viruses causing small mutations
Can eventually make new strains with different genome
What type of virus causes intranuclear inclusion bodies?
dsDNA enveloped virus
What is inclusion body rhinitis?
Caused by cytomegalovirus (dsDNA enveloped) - damages respiratory epithelium causing ulceration and inflammation
nuclear inclusion bodies - replicate in nucleus
What are 6 ways we can demonstrate characterisitc lesions?
Inclusion bodies Virus isolation PCR Demonsrating viral antigen Immunofluorescence Latex agglutination
How do we PCR RNA viruses?
Convert to DNA first
How do we demonstrate viral antigens?
Within lesions - transmission electronmicroscopy or immunohistochemistry (RAT)
Polycloncal antibodies
Monoclonal antibodies - targets one epitope of virion
How does latex agglutination work?
Coloured latex spehres coated with viral antibodies to detect antigens (or other way around)
What are 4 serology methods?
Agar-gel immuno-diffusion (not sensitive)
Haemagglutination
Doubling dilutions
Haemagglutination inhibition
What is an ELISA?
Enzyme linked immunosorbant assay
antibody onto plate, antigen attaches
Colour change occurs
What are 4 types of vaccines?
- Live
- Inactivated
- Subunit virus vaccines
- DNA virus vaccines
What are 4 types of live vaccines?
- Live pathogenic
- Live attenuated
- Heterologous
- Recombinant
How do heterologous vaccines work?
They are of a closely related virus species of lesser virulence that provides immunity (cross reacts) with the one we want
Canine adenovirus 2 used to provide immunity for CA1
What is a live recombinant virus?
Gene for immunogenic protein from one pathogenic virus inserted into another non-pathogenic virus
3 advantages of live vaccines
Good immune response that is long lived
1 dose required
cheap
3 disadcanages of live vaccines
Danger of reversion to virulence
Severe disease risk in immunocompromised
vaccine must remain alive (storage hard)
How are inactivated vaccines prepared?
Virus grown in vitro and inactivated with chemicals (formaldehyde or B-propiolactone)
Mixed with oil for slow release and long lasting immunity
Disadvantages of killed vaccines
Need booster
Expesive to prepare
More antigen needed than attenuated
Local reactions at site due to adjuvants used
Limited cell mediated response, okay humoral
Advantages of killed vaccines
Cant cause disease
Easier to store
What are 3 examples of adjuvants
Aluminium salts (good antibody, poor CMI response)
Liposomes and immunostimulating complexes
Complete freunds adjuvant
List 4 types of innovative vaccines
DNA vaccine
mRNA vaccine
Subunit vaccine
Virus vector vaccine
All code for antigens
How are subunit virus vaccines made?
By fractionation of whole virus preparations
Antigens produced using recombinant DNA technology
How do DNA virus vaccines work?
Plasmid DNA encoding antigenic protein injected (intramuscular or intradermal) that is expressed in host
Antibody, T cell activation, cytotoxic T cells produced
