Virology Flashcards
1
Q
Viral envelope: influenza virus
A
- Hemagglutinin: surface glycoprotein, attaches to sialic acid residues of host cell surface
- Neuraminidase: surface spike, aids in release of virus from host cells
2
Q
Viral proteins: matrix proteins
A
- links envelope and capsid: stabilisation
- can drive final assembly process
- important determinant of budding location
- viral capsid is made of proteins, which assemble without E requirement
- Capsids can be icosahedral or helical
- Icosaheral viruses have 20 facets (each an equilateral triangle. and 12 vertices, which results in 5- 3- and 2-fold symmetry.
- All known human viruses w helical capsids are naked.
3
Q
DNA viruses
A
- Enveloped (dsDNA)
- Pox
- Herpes
- Hepadna
- Naked capsid (dsDNA)
- polyoma
- papilloma
- adeno
- parvo
4
Q
RNA viruses
A
- RNA
- Naked
- Picorna
- Calici
- Enveloped
- Toga
- Flavi
- Corona
- Naked
- RNA
- RNA
- Enveloped
- Rhabdo
- Filo
- Orthomyxo
- Paramyxo
- Bunya
- Arena
- Enveloped
- RNA
- +/- RNA
- double capsid
- reo
- RNA via DNA
- Retro (enveloped)
- RNA via DNA
5
Q
Baltimore classification of viruses: Class I
A
- Class I: dsDNA
- Papilloma, polyoma, herpes, adeno, pox
- some can transform cells
- host enzymes transcrobe IE or E mRNA
- E-proteins: replicate parental DNA & late (L) mRNA;
- L-proteins: assemble into capsids
- Capsids: incorporate the viral DNA to make mature virus
6
Q
Class II
A
Class II: ssDNA
- very small (parvum=small), circo- or parvo-virus (linear so susceptible to DNAses)
- replication occurs in nucleus
- form a (-) strand -> template for (+) strand
- require cell enzymes
- mRNA translated into viral proteins
- NOTE: no immediate early or early proteins
- viral proteins: make up capsids
- viral DNA is encapsidated in progeny virus
- Parvovirus can only replicate when cells are actively replicating
- icosahedral, non-enveloped
7
Q
Class III
A
Class III: ds RNA Virus
- dsRNA: cannot function as mRNA; class III must package an RNAP to make mRNA after infection of host cell
- genomes segmented
- RNA-dependent RNAP in virion
- Ex. Reo-, Birnaviruses, rotavirus
- ds RNA -> transcribed to viral mRNA (v-mRNA) by virus-associated RNA-dependent RNAP
- v-mRNA: translated to structural and non-structural proteins:
- viral proteins to form immature capsid
- mRNA packaged into immature capsid, then copied w/in capsid to form ds RNA
- Rotaviruses, members of Reoviridae
- acute gastro in infants and young children
- icosahedral
- 11 dsRNA segments
- RNA replication: concurrent w packaging of genome segments
8
Q
Class IV
A
Class IV: (+) sense RNA viruses
- Divided into IVa & IVb
- always infectious w/o viral proteins
- ends of genomes often modified w caps
- Ex. Picorna-, toga-, corona-, flaviviruses, dengue
IVa
- polyprotein: post-translational cleavage make multiple viral proteins
- non-structural proteins: transcribe parental (+) RNA into (-) RNA whih in turn is transcribed to (+) RNA
- Structural proteins: make up capsids, incorporate viral RNA - progeny virus
IVb
- stuctural proteins (not one polypeptide)
- parental RNA transcribed into (-) RNA by viral non-structural proteins
- ss (-) RNA -> transcribed into (+) RNA (many copies)
- Capsid incorporates the (+) RNA, other viral proteins -> progency virus
IV: Picornaviruses
- naked, small, icosahedral
- genome is mRNA (naked genome is suffcient for infection)
- virus replicates in cytoplasm, most are cytolytic
- v-RNA: translated into polyprotein; cleaved into enzymatic & structural proteins
- include poliovirus, hepA, rhino- and enteroviruses
9
Q
Class V
A
Class V: ss (-) sense RNA viruses
- more diverse than + sense, larger
- segmentation common
- genome by virus-specfic polymerase (premade); reads (-) RNA -> forms (+) RNA
- assembly of capsid -> incorporation of genomic RNA and viral proteins, including the virus RNAP -> progeny virus
- Ex. Filiviruses, Orthomyxo-, Bunya- (Hantavirus), Paramyxo-viruses
10
Q
Class VI
A
Class VI: ss (+) sense RNA viruses (RT)
- 2 copies of +ve strand RNA (not ds); premade RT generates ds provirus
- retroviruses (HIV)
- Provirus: integrates into host genome, template for synthesis of viral mRNA
- Viral mRNA: viral non-structural and viral structural proteins
- not directly infectious on its own
- Non-structural proteins: may be RT and other polymerases
- Structural proteins: assemble into the capsid
- Mature virion: the capsid incorporates viral genome AND the nucleoproteins including RT -> progeny virus
11
Q
Class VII
A
Class VII: ds DNA viruses, ssRNA intermediate, RT
- Ex. Hepadnaviruses (HBV)
- VII: partially ds DNA virus comes in w its own RT
- core is stripped of nucleic acids
- fills in gaps
- ds supercoiled DNA
- pre-genomic RNA
- structural proteins made and then assemble into a capsid
- pre-genomic RNA goes into capsid; this is ss
- maturation: RT makes a RNA-DNA hybrid in capsid
- RNAase activity digests RNA
- DNA polymerase activity makes the partially dsDNA
- comes out of Golgi and goes out of cell
- VII: HBV
- enveloped virion w partially ds circular DNA genome
- replication is thru a circular RNA intermediate
- virus encodes and carries RT
- HBV has a strict tissue tropism to liver
- HBV genome can integrate into host chromosome
12
Q
Defective virus
A
- complete virus particle BUT unable to replicate w/o helper virus (lacks full complement of genes for complete lifecycle)
- Ex. Hep D requires Hep B to replicate
13
Q
Pseudovirions
A
- contain non-viral DNA, infectious but do not replicate
14
Q
Viroids
A
- infectious, subviral particles
- small, circular ssRNA genomes
- mainly cause plant diseases
- Hep D appears to be a viroid-lke entity (enclosed in Heb B)
15
Q
Virophage
A
- Sputnik: 18 kb circular ds DNA, icosahedral virus (50 nm)
- grows only in a strain of mimivirus w/in infected amoeba
16
Q
Host defenses
A
- non-specific
- interferon
- Type I: IFN-alpha & beta
- Type II: IFN-gamma aka macrophage activation factor
- complement
- other cytokines
- interferon
- specific
- Ab production
- specific immune system
17
Q
Immunopathology
A
- immune response to viral infection can cause tissue injury, i.e. group specific Ab from previous infection actually protect virus.
- Ex. CMV (circulating immune complexes -> depositis -> arthritis)
- Ex2. Dengue (hemorrhagi shock sydnrome: fixation of complement by circulating immune complexes -> release of products via complement cascade -> sudden increase in vascular perm, shock, death
18
Q
Persistent infection & latency
A
- Persistent infection: Ex. Adenovirus; not totally resolved so certain number of viruses constantly produced; infection w/o cell death, selection of ideal target cell subsets (chronic - nonlytic, productive); viruses apply numerous avoidance strategies to persist
- direct selective pressure to suppress infected host’s innate and/or adoptive immune system
- viruses can alter/interfere w the processing of viral peptides by professional APC
- can downregulate co-stimulator and/or MHC molecules (required or T cell signaling)
- inhibit the differentiation of dendritic cells; infect effector T and B cells directly.
- Latency: virus goes there and hides even when host is healthy; recurrent infection;
- modulation of viral gene expression
- viral subversion of cell apoptotic pathways
- avoidance of clearance by immune system
19
Q
Basic steps of viral disease
A
- acquisition
- initiation of infection at primary site
- incubation period (amplification, spread to secondary site)
- replication in target tissues
- immune response (limit & contribute)
- transmission
- resolution or persistent infection
31
Q
EBV (HHV-4)
A
- >90% of EBV-infected people intermittentl shed the virus for life (even asymptomatic)
- approx. 70% of the US population infected by age 30
- causally associated w endemic Burkitt’s lymphoma (AfBL), Hodgkin disease, nasopharygneal carcinoma (NPC)
- has 3 potential outcomes:
- replicate in B cells or epithelial cells permissive or EBV replication
- cause latent infection of B cells in presence of competent T cellls -> Downey cell association (atypical T cells, enlarged cell & nucleus)
- stimulate and immortalize B cells
- Note: both B- & T-cells required for antigenpresentation
32
Q
HHV-8 (KSHV): Kaposi’s sarcoma
A
- tumour of bv wall
- rare in people not infected w HIV
- common in HIV+ people frequently detected tumour in AIDS Pt
- pink, red, or purple lesions on skin and mouth
33
Q
Merkel cell polyomavirus (MCV)
A
- Merkel cell carcinoma (MCC) highly aggressive neuroendocrine carcinoma of skin w a high propensit of recurrence and metastasis
- 5-year disease-specific survival rate ~60%
- MCV associated w most MCC cases (subset of MCC, 20 - 30%, do not harbour MCV and apparently have a distinct pathoetiology)
