Virology - Orthomyxovirus and retroviruses Flashcards
What are the main viruses in the orthomyxovirus family?
Influenza
What classification is orthomyxovirus genome?
Negative sense single stranded RNA
Group 5 of Baltimore classification system
Is orthomyxovirus enveloped?
Yes
What shape is orthomyxovirus?
Pleiomorphic - many different shapes
What is found in the lipid envelop of orthomyxovirus?
Peplomers - large glycoprotein spikes that protrude from the surface
What does having an lipid envelope cause in viruses?
Sensitivity to heat, acids
Are labile under normal environmental conditions
What symmetry does orthomyxovirus nucleocapsid have?
Helical
What are the two different types of cell surface peplomers in orthomyxovirus?
HA - haemagglutinin
NA - neuraminidase
Give the names eg. H1N1
What is haemagglutinin (HA) responsible for
on orthomyxovirus?
Attachment of virus to cells
What does neuraminidase do for orthomyxovirus?
Cleaves sialic acid from viral receptors glycoprotein so the virus can be released from the cell surface by budding
What activates haemagglutinin (HA) (in influenza viruses)?
Host cell proteases cleave it at its hinge region
What does HA1 bind to (in influenza viruses)?
Sialic acid
What does HA2 mediate (in influenza viruses)?
Membrane fusion
Fusion of the viral envelope with the endosomal membrane releasing viral contents into the cytoplasm
What type of sialic acid is found in mammalian respiratory tracts?
Galactose a-2,6 sialic acid
What type of sialic acid is found in wildfowl intestine?
Galactose a-2,3 sialic acid
Why is the type of sialic acid relevant (in influenza viruses)?
Some influenza viruses bind to one type better than the other
What type of sialic acid is found in pigs receptors?
Both a -2,3 and a-2,6 sialic acid expressed on their receptors
So pigs can catch both human and avian influenza
Mutations occur in pigs a lot as well
What type of influenza affects birds?
Influenza A - all subtypes
How many different haemagglutinin subtypes are there (in influenza viruses)?
18
How many different neuraminidase subtypes are there (in influenza viruses)?
11
What cell types are susceptible to influenza?
Ciliated columnar epithelium
Found in the respiratory tract
Where is ciliated columnar epithelium found?
Respiratory tract - sinuses, larynx, trachea, bronchi and bronchioles
How many segments of the influenza genome are there?
8
Which genome segments code for RNA polymerase (in influenza viruses)?
1,2,3
Which genome segment codes for haemagglutinin (in influenza viruses)?
4
Which genome segment codes for neuraminidase (in influenza viruses)?
6
How does influenza replicate its genome?
-ve sense RNA converted to +ve sense by RdRp
The +ve sense then makes viral proteins and is copied to make many -ve sense RNA which is then packaged
Where is RdRp found in influenza viruses?
Attached to the -ve sense RNA already
Cant make one bcos they are -ve sense not +ve sense
What triggers HA2 membrane fusion (in influenza viruses)?
Drop in pH in endosome
Where does genome replication/conversion to +ve sense RNA occur (in influenza viruses)?
Cell nucleus
What does antigenic drift cause changes to in influenza viruses?
The surface proteins haemagglutinin and neuraminidase
What does antigenic shift cause in influenza viruses?
Genome segments from two different viral strains are reassorted
Where does influenza virus assenbly and budding occur?
On the apical side of the epithelial layer - budding into the lumen of the airway
How does influenza virus enter the host?
Faecal oral route in birds
Small particles inhaled into lungs
Larger particles from coughs etc. into upper airways
How does influenza interfere with cell function?
Causes apoptosis
This causes inflammation, fever etc.
What causes more virulent strains of avian influenza?
Mutations causing cleavage of haemagglutinin in most tissues rather than just respiratory. This causes generalised infection as infectious virions can be released everywhere
What are the avian influenza designations and what determines them?
Low pathogenic avian influenza (LPAI)
Highly pathogenic avian influenza (HPAI)
The potential of the virus to kill chickens
What are tee main symptoms of highly pathogenic avian influenza?
Cyanosis
Bleeding from everywhere
Death
How do you diagnose avian influenza?
PCR assay to detect matrix protein gene
Then test for H5 and H7 genes
Then sequence to determine if there is enhanced cleavage
How do we control avian influenza?
Vaccination not permitted
Reporting, rapid action and culling
Surveillance
What are the symptoms of equine influenza?
High temperature
Nasal discharge
Dry cough
How is equine influenza spread?
Aerosols from coughing
Highly contagous
What are the two subtypes of equine influenza?
H3N8 and H7N7
How is equine influenza diagnosed?
PCR
Haemagglutination inhibition assay
How is equine influenza controlled?
Vaccination - inactivated with multiple different lineages
How is equine influenza treated?
No treatment, just supportive nursing care
What is the classification of retrovirus genome?
Positive strand RNA virus with DNA intermediate
Group 6 of the Baltimore classification system
The genome is diploid (the only one)
What enzyme is used by retroviruses?
Reverse transcriptase
What is an example of a retrovirus in humans?
HIV - AIDS
What are some conditions caused by retroviruses?
Inflammation
Neurodegeneration
Immunodeficiency
Cellular transformation
Do retroviruses have an envelope?
Yes
What symmetry does the retrovirus nucleocapsid have?
Icosahedral
What is found in the retrovirus capsid?
Two copies of the positive sense RNA - dimer
Reverse transcriptase - 30 molecules
What does integrase do in retroviruses?
Helps integrate the converted double stranded viral genome into the host cell genome
What does protease do in retroviruses?
Converts immature virions that are budding from the cell into mature, infectious virions
Cuts up the gag-pol polyproteins
What does the relationship between envelope glycoproteins and host cell receptors mean in retroviruses?
The specific receptors responsible for virus attachment are unique to each retrovirus
This makes retroviruses species restricted
What are the three major regions of the retrovirus genome?
Gag
Pol
Env
What does the gag region of the retrovirus genome code for?
Structural proteins eg. capsid, matrix proteins
What does the pol region of the retrovirus genome code for?
The enzymes eg. reverse transcriptase
What does the env region of the retrovirus genome code for?
The peplomers - transmembrane glycoproteins
What does the retrovirus genome have on its ends?
5’ cap
Poly A tail
What does the reverse transcriptase enzyme have that allows it to produce double stranded DNA?
RdDp and DdDp (not RdRp, look closely)
So is a DNA polymerase that can copy either a DNA or an RNA template
Where does DNA synthesis occur for retroviruses?
In the cytoplasm
What is the hand domain of reverse transcriptase?
The part that grabs the viral genome
What are the finger and thumb domains of reverse transcriptase?
The walls of the nucleic acid binding cleft
What is the palm region of reverse transcriptase?
The base that contains the DNA polymerase active site
What is a risk of reverse transcribing the retroviral genome?
It has no proofreading function
This causes a high error rate
What part of the retrovirus gets deposited in the cytoplasm when it enters a host cell?
Only the capsid containing the genomic material
Where does reverse transcription occur? Why?
Inside the capsid in the cytoplasm
Prevents DNA being degraded
What is the term for when the double stranded DNA has been integrated into the host cell genome but is transcriptionally inactive?
Provirus
What converts a provirus to a functioning retrovirus?
Host cell RNA polymerase starts transcribing it
Where do retroviruses assemble?
On the inner surface of the plasma membrane
What do budding retroviruses have?
An electron dense ring showing the gag pol polyproteins that are on the inner leaflet of the envelope
What do mature retroviruses have?
A distinct conical structure inside the retrovirus
What converts immature retroviruses to mautre retroviruses?
Protease
What are oncogenes?
Genes that cause cancer
How do retroviruses cause cancer? 3 ways
Contain stolen oncogenes in their genomes
Can stimulate overexpression of endogenous oncogenes
Can produce viral proteins that are oncogenic
How may cancer cases have an infectious aetiology?
1 in 6
What is the viral oncogene which causes the malignant changes induced by the Rous sarcoma virus?
v-src
What is the v-src oncogene?
A tyrosine kinase which specifically phosphorylates tyrosine residues of critical cellular substrates in cells
What does v-src cause?
Activation of oncogenic transduction pathways and therefore tumourgenesis
What is the normal cellular counterpart of v-src?
c-src
Very similar to v-src but found in host cells
What is different between v-src and c-src?
c-src is tightly regulated
v-src lacks 19 amino acids in the regulatory C terminal region of the genome
c-src is maintained in an inactive state, only activated by specific stimuli
What are oncogenes required for and not required for by viruses?
Not required for virus replication
But are responsible for cellular transformation and development of cancer
What is v-sis?
FeLv - growth factor that transforms fibroblasts into leukemia/sarcoma
What is v-erb?
Avian leukosis virus - growth factor receptor
What is v-fms?
Feline sarcoma virus - tyrosine phosphokinase
What is v-myc?
Feline/avian leukaemia virus - nuclear transcription factor
What is the name for viruses that contain oncogenes?
Acute transforming retroviruses
What are acute transforming retroviruses?
Retroviruses containing oncogenes that integrate into the host genome and induce tumours rapidly
What does a replication defective retrovirus mean?
Through obtaining an oncogene from the mammalian host, the retrovirus has lost an essential gene that controls the ability to replicate
What is a replication competent retrovirus?
A retrovirus that can still replicate while containing an oncogene in its viral genome
How do replication defective retroviruses replicate?
With the help of an endogenous retrovirus that can produce the proteins that its missing
Or if the cell is coinfected with another virus (helper virus) which can supply the proteins
What is a non-acute retrovirus?
Induce tumours with a longer latency/over a long period of time
What is a proto-oncogene?
Host cell genes that regulate cell growth eg. encode growth factors
How do non-acute retroviruses cause tumours?
They cause insertional mutagenesis by influencing host cell proto-oncogenes with their powerful promoters on inserted proviruses which disrupts host cell growth regulation.
Also disrupt a tumour suppressor gene
What are some examples of non-acute retroviruses?
Avian leukosis virus Murine leukaemia virus Murine mammary tumour virus Feline leukaemia virus Non require a helper virus to replicate
What is something else that can cause oncogenesis other than viral genome?
Viral regulatory proteins
What spreads equine infectious anaemia?
Biting insects eg. horseflies, stable flies and mosquitoes
Also colostrum to foals
How does equine infectious anaemia manifest?
Acute - fatal within a month
Chronic - 8-12 months
Inapparent carriers - after about a year
What cells does equine infectious anaemia infect?
Monocytes and macrophages
What organs/tissues does equine infectious anaemia infect?
Spleen
Liver
Tissues with lots of macrophages
What are the clinical signs of equine infectious anaemia?
Fever - spike in virus causes a spike in fever
Anaemia
Thrombocytopenia
Wasting
Hoe is it diagnosed?
Lots of testing
Coggins test
PCR
What is the Coggins test?
Agar gel immunodiffusion test
Antibodies precipitate when bound to a capsid antigen
Is there a vaccine for equine infectious anaemia?
In china, not in UK
What is feline leukaemia virus?
An exogenous gamma retrovirus
How is feline leukaemia virus transmitted?
Shed at mucosal sites
Transmitted via saliva or milk
What disease syndromes are associated with feline leukaemia virus?
Neoplastic disorders bone marrow suppression Neuro disorders Immunodeficiency etc.
When can feline leukaemia virus cause oncogenesis?
When it integrates into the host genome in close proximity to cellular oncogenes c-myc
What type of cancer is most common in feline leukaemia virus?
Lymphoma
How do you diagnose feline leukaemia virus? What do you test for
PCR - detects provirus
Indirect immunofluorescence procedure o - detects p27 core protein
Can you vaccinate against feline leukaemia virus?
Yes but they do not eliminate pre-existing infections
How to prevent feline leukaemia virus?
It is a labile environment so disinfection can kill it
Regularly test cat colonies
What does Jaagsiekte sheep retrovirus cause?
Infectious pulmonary adenocarcinomas
How is Jaagsiekte sheep retrovirus spread?
As aerosolised pulmonary fluid between sheep in close contact
What is the cellular receptor for Jaagsiekte sheep retrovirus?
Hyaluronidase 2 on many different types of cells
What type of retrovirus is Jaagsiekte sheep retrovirus?
Simple retrovirus that doesnt contain a viral oncogene
How does Jaagsiekte sheep retrovirus induce cellular transformation?
It produces a protein called Env protein that is responsible for oncogenesis
What defines the Jaagsiekte sheep retrovirus tissue tropism?
The LTR region and the env gene product
What is the retrovirus ligand for the hyaluronidase 2 receptor?
The env glycoprotein
What are the two specific cell types that the retroviral LTR can work in?
Alveolar type 2 pneumocyres
Bronchiolar cells
So is confined to the lungs
What time period does Jaagsiekte sheep retrovirus act in?
Lung tumours in as little as 10 days
How do you diagnose Jaagsiekte sheep retrovirus?
ELISA
PCR
Can you vaccinate against Jaagsiekte sheep retrovirus?
Nope
How do you prevent Jaagsiekte sheep retrovirus?
Depopulation measures
Remove clinically infected sheep from flock
