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Virology- reoviridae
viruses
63
Veterinary Medicine
Undergraduate 3
05/31/2012

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Term
reoviridae viruses =
Definition
rotaviruses
orbiviruses
Term
reoviridae genome =
Definition
dsRNA
Term
reoviridae ENV?
Definition
no!
Term
shape of reoviridae =
Definition
near spherical
Term
commonest cause of neonatal diarrhoea in calves and lambs=
Definition
rotavirus
Term
capsid of rotavirus =
Definition
3layered icosahedral capsid

(3layers of protein)
Term
how long does rotavirus survive in enviro?
Definition
6months -1yr

resistnat to dessictaion and UV light
outer capsid = bile and acid resisitant
Term
in inner capsid of rotavirus =
Definition
12 copies of RNA pol
11segments of dsRNA
capping enzymes
Term
rotavirus replicates in...
Definition
...intestine
Term
infection of rotavirus by...
Definition
...ingestion
Term
for rotavirus to become infectious it requires...
Definition
...predigestion by trypsin (a protease) to gte rid of outer capsid

This restricts rotavirus infection to the intestine as not activated until in intestine
Term
rotavirus infects cell via...
Definition
...adhesion and endocytosis

intermediate capsid inserts proteins into cell mb of endosome = derc IC Ca2+ = change in intermediate capsid = disintergration of endosome and inner capsid/core in cytoplasm
Term
mRNA synth of rotavirus occurs in...
Definition
...virus core

does this to hide dsRNA as dsRNA = a potnent inducer of IFN reaction
Term
protein synth of rotavirus occurs in...
Definition
...cytoplasm, ER mb and golgi body
Term
what is done to prevent initiation of hosts immune response?
Definition
dsRNA hidden in core and - RNA strand only synth in core (as both of these would otherwise trigger IFN immune response)
Term
rotavirus exits host cell via...
Definition
...cell mb budding and then gets rid of lipid ENV (as rotavirus has no ENV)

or cell lysis (larg no of virus released)
Term
the 11 segments of dsRNA in rotavirus encode what?
Definition
9 ds RNAs encode single proteins (monocystronic)

2 dsRNAs produce a peptide thats cleaved into 2 proteins

so in total 13virus proteins are made
Term
inclusion body =
Definition
large amorphous mass of viral protein where viral replictaion occurs
Term
Rs of rotavirus =
Definition
sialic acid

therefore may be zoonotic, spread by insect vectors
Term
are humans at risk of calf ans sheep rotavirus?
Definition
no
Term
do you have to have marked/gross intestinal pathology for diarrhoea to occur sue to rotavirus?
Definition
no
Term
rotavirus enterotoxin =
Definition
NSP4
Term
NSP4 causes ...
Definition
...direct inhibition of SGLT1
...activateion of Ca2+ release from ER

=diarrhoea
Term
activation of Ca2+ release from ER of microvilli due to NSP4 causes...
Definition
1. distruption of cytoskeleton, cell perm and tight junctions = water leaks, cell out
2. loose microvilli = derc SA = decr absorption
3. decr dissacharides such as lactulase = bacteria fermentation of lactose in neonates =osmotic secretion
4. incr ca2+ contributes to virus synth and stability
5. incr Ca2+ causes infected cell to secrete amines, peptides, NO and cytokines = activate neteric NS = activate crypt cell secretion and gut motility
Term
most susceptible to rotavirus infection =
Definition
young
Term
rotavirus is a dz of ________.
Definition
intensifictaion
Term
dx of rotavirus =
Definition
1. EM of faecal rotavirus - looks like wheel
2. strains distinguished by diff sizes of their RNA segments (diff banding pattern of RNA on polyacrilamide gel)
3. Ag capture ELISA test
4. latex agglutination tests
Term
Abs against rotavirus...
Definition
...rotavirus virus proteins on outer capsid = neutralising effect - stop virus adhering to cell mb

Abs have to be in SI (no gd in blood)
Term
most effective protection from rotavirus =
Definition
IgA (from maternal milk therefore calves reared on artificial milk are more at risk of dz)
Term
rotavirus vacc?
Definition
killed vacc used to boost maternal Ab levels
Term
disadvantages of killed rotavirus vacc =
Definition
-many rotavirus strians, not all included in vacc
-annual boosters req
Term
name 2 orbivirus
Definition
Bluetongue virus (BTV)
african horse sickness
Term
orbivirus structure and replication same as...
Definition
...rotavirus
Term
most imp sheep dz in the world =
Definition
BTV
Term
BTV affects what sp?
Definition
SHEEP
cattle
camelids
Term
BTV spread by...
Definition
...midges-cullicoid imicola

(local UK midges can also act as vectors if weather hot enough)
Term
cullicoide imicola =
Definition
small insects (<5mmm long)
short mouthparts
chews through sheep(hosts) skin = ruptures bvs=pool of blood=sucks up blood
Term
BTV replicates where?
Definition
in local areas of midge bite site
Term
BTV infects...
Definition
...reticulo-endothelial cells:
-dendritic cells
-macro
-lympho
-endothelial cells
Term
BTV spreads around body as...
Definition
...cell associuated virameia, howevere it can be free in blood
Term
clinical signs of BTV =
Definition
1. fever - due to damaged endothelium and leukocytes (virus qu. gd at ducking IFN response)
2. inappentance
3. conjunctivitis
4. hyoeraemia (incr blood in organs, mucous mbs and coronary band)
5. drooling
6. lameness
7. oedema (due to leaky bvs)-pulm oedema = resp distress = cyanosis = 'blue tongue', liquid out of nose from lungs - chokes animals
Term
if sheep with BTV got a blue tongue =
Definition
prognosis is BAD!
and it is not as common a sign of BTV as you would think!
Term
on PM what do BTV infected lungs look like?
Definition
v red, heavy lungs with froth in trachea
Term
in general what sp are more resistant to BTV?
Definition
cattle and native african breeds
Term
what must BTV do in midge b4 it can reinfect host?
Definition
replicate in midge gut & spread to salivary glands of midge
Term
does BTV infection harm the midge?
Definition
no

not cytopathic in insect cells 9doesnt want to kill vetcor, need vector to spread and reinfect host)
Term
how long does it take midge to become infectious?
Definition
14days at temp of 10C
Term
replication of BTV in cullicoides is _____ dependent
Definition
temp
Term
a single bite of carrier insect ALWAYS infects sheep with BTV, but an injection of BTV of similar quantity isnt always infectious. WHy?
Definition
insect saliva effects host immunity and viruses pathogenicity
Term
midges overwinter as...
Definition
...eggs in soil or manure

unlikely virus can survive in wintering insect eggs
Term
transovarial transmisison of BTV in insects?
Definition
little evidence
Term
viraemia in cattle =
Definition
longer than sheep and doesnt cause as severe clinical signs
Term
carriers of BTV =
Definition
cattle - BTV may be surviving winter in cattle lymphocytes - gamma delta Tcells can become persistantly infected(viraemia).
Term
how is virus overwintered in cattle viraemia re-activated?
Definition
midge bite in summer = inflam = attract and activate lymhpho =activate and release virus from lympho
Term
what midge feed at the start of summer becomes infected with BTV?
Definition
the midge feed ~ 4hrs after 1st midge feed, as it take ~4hrs to reactivate virus and thereofre for the cow to become an active/infectious carrier
Term
proteome =
Definition
full complement of proteins produced by a particular genome
Term
midge saliva proteome =
Definition
1. inhibit Xa = inhibit blood coagulation
2. collagenase = soften tissue and clot buster
3. apyrase = ATP and ADP to AMP = vasodilation
4. stop Thelpre 1 and incr Thelper 2 response = wrond immune response to tackle virus
5. insect trypsin can cleave virsu outer capsid = enhance BTV infectivity
6. cause inflam response= incr cells in local area of viral infection for virus to infect
Term
vacc for BTV?
Definition
1. inactivated/killed BTV8 strain
2. live attenuated
3. virus like particle
Term
strain of BTV seen in UK =
Definition
BTV8
Term
inactivated/killed BTV8 vacc =
Definition
specific - only effective against BTV8 strain
variable efficacy
safe
used in UK and eliminated BTV8 strain outbreak
Term
why dont we use the live attenuated BTV vacc in UK anymore?
Definition
may revert to virulent strain!
Term
virus like particle BTV vacc =
Definition
inner and outer capsid proteins made in bacculovirus get strong neutralising Ab response against outer capsid = protect from clinical dz, but may not prevent infection or carrier status developing. Safe as no nucleic acid = no replication
Term
is BTV currently a problem in UK?
Definition
no :)
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