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31 Cards in this Set
- Front
- Back
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How many genera of Reoviridae are there and what form does there nucleic acid take ?
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9
dsRNA |
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What genera of Reoviridae is the commonest cause of neonatal diarrhoea ?
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Rotavirus
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How many capsid layers do rotaviruses have and what properties does this confer on them ?
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Three
Outer - sticky projections grab host cell Intermediate - (12 copies) RNA polymerase, - internal synth of viral mRNA Inner - capsid has 11 segments of dsRNA lining it |
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What morphology is typical of rotaviruses?
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3 layered, non enveloped Icosahedral capsid
Confers good env survival, acid, bile, desiccation & UV resistant survive on pasture from year to year. Quite big |
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What must happen to rotaviruses before they can infect an enterocyte ?
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Trypsin / acid degradation of outer capsid
hence restriction of infection site |
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Post binding to enterocytes rotaviruses enter cells via ---------- and avoid endosome digestion by -------- [Ca]. they also incorporate there ----- capsid in to the endosome ------- disrupting it.
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endocytosis
decreasing outer membrane |
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What advantage does internal +sense RNA synthesis confer to rotaviruses ?
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Prevents cell detecting viruses dsRNA & signalling infection - interferon response.
ssRNA exits via holes in capsid to cytoplasm |
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Once rotaviruses +sense ssRNA is in the cytoplasm it initiates …….
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Protein synthesis.
Inner capsid assembly incorporating +sense RNA triggering -ve RNA complementary strand synthesis |
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What unique final assembly do rotaviruses employ ?
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outer capsid proteins made in RER, a
ssociate with cell membrane & bud inner capsule through to golgi. End with lipid free outer capsid. Don’t have to kill cell to get out - can escape by lysis or exocytosis. |
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What unique exit strategy can rotaviruses employ and how does this advantage the virus ?
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escape by lysis or exocytosis
don't have to kill cell to exit so more particles can be replicated by one host cell |
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What receptors on host cells can rotaviruses bind to enter cells ?
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Sialic acid, heparin, intergrins acts as receptors,
but not specific so not spp specific |
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Why can diarrhoea caused by rotaviruses occur without marked / prior to pathology ?
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Rotavirus Non Structural Protein 4 effects enterocytes by
- blocks disaccharideases on lumenal membrane - blocks Na Glucose symport - both increase osmotic P - sugar fermented by bacteriain GIT = GAS, & osmotic P - loosens intracellular junctions - cytokine, amine release stimulated |
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How do rotaviruses cause tight junction loosening ?
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CA released for ER
- mediates cell cytostuctural relaxation - inhibits SGLT1 |
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How does rotaviruses mediated cytokine and amine release enhance the diarrhoea?
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Cytokines
- vasoactive - increase cell permeability - increase fluid & molecule loss to lumen - increase motility of GIT - increase mucous secretion |
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How should rotavirus infections be treated ?
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Supportive care
electrolytes & fluids |
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how does normal cell function enhance diarrhoea in rotavirus infections?
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Crypt cells function is unaffected so endogenous pumping Cl into lumen ongoing
NSP4 enhances crypt cell Cl secretion. |
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How can rotavirus infections be diagnosed ?
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Traditionally - fecal sample under EM
Now strains distinguished by differing RNA segment sizes in agarose gel. Dip stick on farm - 2 lines = +ve. |
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When can gene reassortment occur in rotaviruses ?
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2 or more viruses infect same host - swap bits
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How is immunity to rotavirus infections mediated ?
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Ab to outer capsid VP 7 & 4.
Needs to be lumenal Continuous IgA in milk = protective low damage does not = dz animals may build up immunity by weaning stage. |
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What strategies can be employed to counter rotavirus infections ?
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Killed vaccines used to boost maternal antibody levels
Must continue to feed colostrum/milk to dairy calves But many strains - not all included in vaccine Annual booster required |
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What type of virus is blue tongue, what spp does it affect and what cell type ?
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Orbivirus
sheeps, cattle, camelids wide variety of cell types |
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What does this image of midge bites on a sheep show ?
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Inflammation round bite site -
happy virus infecting lots of cells viraemia spreads to distant sites & other midges |
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What are the clinical signs of Blue tounge virus ?
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fever, loss of appetite, conjunctivitis - because BVs inflammed, hyperaemia of mucus membranes, drooling, lameness - hyperaemia of coronary band.
Inflammation in lungs and resp tract - oedema in lung = cyanotic = blue tongue. (often don’t see) symptoms more severe in sheep than cattle. |
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How does Blue tongue cause death ?
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Pulmonary oedema
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Blue tongue in insects is not cytopathic but one bite of what mammalian spp host is ---------.
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sheep
infective |
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How may blue tongue virus infectivity be increased by midges ?
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Insect trypsin may cleave virus outer capsid protein and enhance virus infectivity (by sugar digesting enzymes)
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Does insect saliva have an effect on the virus pathogenicity?
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Yes
- factors in midge saliva affect coagulation pathway, - factor Xa inhibitor, collagenase, - apyrase - prevents ATPO dependent platelet aggregation, - vasodilator proteins = encourage virus to replicate and spread at site of infection. |
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What factors were thought to affect blue tongue spread to northern climes ?
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Replication of Blue Tongue virus in culicoides is temperature dependent - 14 days in a row staying above 10C needed for transmission of virus.
Unexpectedly turned up in 2007 ermany / Netherlands wind spread to UK |
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What made blue tongue potentialy endemic in the UK ?
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Overwintering: midge adults don’t survive in cold weather. Carrier animals (cattle) must be involved in overwinter survival
Virus overwinters in host T-lymphocytes, T cell activation = virus is reactivated Midge bites causes inflammations - activates T-lymphocytes & therefore virus (Inflamed fibroblasts express WT1 ligand which activates T-cells via WT-1 ligand, which then release virus) |
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How long does reactivation take in the carrier from activation to transmissibility?
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4 hours.
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How has BTV8 strain of blue tongue been controlled ?
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Vaccination in control zone - where no infection occurred
with inactivated BTV8 virus strain specific - variable efficacy - Can have live attenuated virus (but recimbination means can revert to virulent) - Virus like particle - inner and outer capsid proteins made in Bacculovirus spontaneously assemble into capsids with no nucleic acid - Strong neutralising antibody responses - protect from clinical disease but may not prevent infection or carrier status developing |
