Caliciviruses

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(No Transcript)
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Themes
Picorna, calici Picorna, Calici Calici Calici
Reo
Persistent infections Antigenic
variation Immune evasion, Emerging
disease Arthropod-transmitted viruses
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Picornaviruses and Caliciviruses
pico- calici-
genome ss RNA ve sense ss RNA ve sense
genome size 8kb 8kb
capsid icosahedral icosahedral
envelope none none
virion size 25 40
Stable in environment
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Replication

• replicate in cytoplasm
• ve sense genome
• (genome RNA is infectious)
• encode viral polymerase
• mature viral proteins generated
• through proteolytic cleavage
• virions released on cell lysis

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PicoRNAviruses
ss, positive sense RNA, icosahedral capsid, 25nm,
and no envelope
Pico small Greek
Positive sense ICOsahedral RNA genome
4 coat proteins VP1, VP2, VP3,VP4 simple capsid
60 capsomere (composed of VP1,2,3)
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Picornaviruses

• Restricted host range (except FMD)
• Resistant in environment
• Transmission faecal-oral (fomites, aerosol)
• Antigenic variation
• Persistent infection (FMD)
• Associated with vesicular disease and
  encephalomyelitis
• Diagnosis usually by ELISA (Ag detection) or
  virus isolation

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Picornaviridae
9 genera Important veterinary viruses
Cardiovirus encephalomyocarditis virus ECMV
Hepatovirus avian encephalomyelitis
Enterovirus swine vesicular disease,
porcine enteroviruses
Aphthovirus foot and mouth disease
Teschovirus porcine teschovirus
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FMDV

• virus extremely infectious
• rapid replication cycle, high virus yield
• large volumes in aerosols, virus stable
• short incubation period
• wide host range
• dissemination pre-diagnosis - virus excreted up
  to 4 days pre-clinical signs mild clinical
  picture in some hosts (sheep)
• carriers - persists in pharynx
• transmitted by animals/contaminated items/
  people/environment, windborne

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Foot and Mouth Disease Virus

• Aphthovirus genus NOTIFIABLE

First animal virus discovered (1898) one of
most contagious viruses
cloven hoofed animals - cattle, pigs, sheep..
low mortality but high morbidity - fever,
oral/feet/teat lesions dairy herds - reduced milk
yield beef cattle - reduced growth
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FMD excretion
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FMD broad host range
Amount of virus shed Clinical picture Sensitivit
y to infection Carriers
amplifier hosts
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FMDV serotypes
endemic in south america, africa, asia, middle
east
7 immunologically distinct FMD types
(serotypes)
SAT3
SAT1
C
Asia-1

• animal with immune response to one serotype is
  not protected against infection
• by a different serotype
• vaccines must contain serotypes of all strains
  circulating in that region

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Foot and mouth disease UK 2001
2030 cases Slaughter policy 9500 premises 4
million animals 40 total 8 billion
Serotype O
FMD-free areas
? illegal importation of W. Asian meat
inadequate treatment of swill fed to pigs
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Control
FMD-free countries post vaccination/eradication
campaigns importation controls - animals, meat,
animal products surveillance and reporting
procedures World Reference Lab UK Ban on swill
feeding (instigated due to 2001 outbreak) -
outbreak UK 2001 - slaughter policy (infected,
contact premises), animal (
personnel) movement controls, disinfection
Endemic countries vaccination (multivalent)
first virus eradicated worldwide smallpox
1977 first animal virus rinderpest
(paramyxovirus) goal 2010 second targeted
virus poliovirus (picornavirus) ongoing
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Caliciviruses
ss, positive sense RNA, icosahedral capsid, 40nm,
no env
EM - Star of David - cup-shaped on capsid
surface (calyxcup)
- single capsid protein - 2 or 3 open reading
frames

• caliciviruses typically associated with
  respiratory,
• vesicular, haemorrhagic disease,
  gastroenteritis
• emerging diseases Rabbit haemorrhagic disease
  virus (RHDV)
• Humans main cause of non-bacterial
  gastroenteritis

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Veterinary Caliciviruses
vesivirus feline and canine calicivirus
vesicular exanthema of swine lagovirus
rabbit haemorrhagic disease virus
European brown hare syndrome virus
Caliciviruses exist in marine species Ocean
reservoir
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Feline Calicivirus
respiratory disease - (40 cases), usually
associated with feline herpesvirus (cat flue)
main clinical feature chronic stomatitis -
nasal/ocular discharge (rhinitis/conjunctivitis,
oral lesions, fever, lameness), can be fatal in
kittens
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Theme virus persistence

• FCV (calicivirus) vs FHV (herpesvirus)
• major viral causes of upper respiratory tract
  disease (cat 'flu) note NOT influenza virus
  (orthomyxovirus)
• upper respiratory tract, mouth ulcers
• FCV - chronic, productive infection
• FHV - periodic virus shedding (due to
  reactivation of latent virus)

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Rabbit haemorrhagic disease virus

• European rabbit necrotic hepatitis - death in 2
  days, acute respiratory/cardiac failure, up to
  95 mortality

Notifiable

• foecal/oral transmission
• (inhalation, insects)
• some rabbits may be carriers
• control inactivated vaccines
• available (infected rabbits)

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Birna- and reoviruses
birna- reo-
genome dsRNA linear segmented dsRNA linear segmented
capsid icosahedral icosahedral
envelope No No
genome size 6 (2 segs) 22 (10-12 segs)
virion size 60 80
replicate in cytoplasm, virus polymerase stable
in environment potential for reassortment
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Bi-rna-viridae
dsRNA, non-enveloped, 60nm
Two segments
RNA genome
60nm
aquabirnavirus
infectious pancreatic necrosis (IPN) fish
avibirnavirus infectious bursal disease chickens
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Infectious pancreatic necrosis (IPN)

• affects young salmon, trout
• high mortality - gut haemorrhage, pancreatic
  necrosis
• Shetland 10 production (gt1 million fish) 2
  million 2001
• IPN ( Infectious salmon anaemia) - major
  threat to salmon
• farming industry

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Infectious bursal disease of chicks IBDV (Gumboro
disease)

• 3-6 week old chicks
• Virus kills immature B-lymphocytes in
• bursa of Fabricius
• Virus kills T-lymphocytes in the thymus
• Causes severe combined immunodeficiency
• Very virulent (VV) strains 50 mortality
• Recovered chicks immunosuppressed
• - increased susceptibility to pathogens
• - decreased efficacy of vaccines
• Vaccination of breeders, chicks

enlarged bursa of fabricius
Notifiable
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Reoviridae
ds RNA, non-enveloped, cubic symmetry, double
capsid, 60nm.
Respiratory Enteric Orphan VIRUS

• Rotavirus
• Orbivirus

11 genera important veterinary genera -
outer capsid (ico)
inner capsid (ico)
capsid - layered
core
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Rotavirus
latin 'wheel'

• a major cause of diarrhoea (scours) in very
  young calves,
• - foecal/oral transmission (waterborne)
• - vaccines available for dam - boost colostral Ab

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Rotavirus infection
infection of enterocytes at TIPS of villi in
small intestine
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Orbiviruses
latin 'ring'
Bluetongue African horse sickness
Theme Arthropod transmitted
arboviruses - replicate in insect vectors
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Bluetongue

• Africa, Middle East, Asia, Americas
• 24 serotypes antigenically diverse
  (vaccination implications)
• Disease in sheep (deer)
• Cattle important reservoirs (subclinical)
• Transmitted by midge vectors late summer

fever, changes to the mucous linings of the
mouth, nose (cyanosis of tongue), coronary band
reproductive disorder, vascular disease

Notifiable disease
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Culicoides spp. 'no-see-ums'

• female midges feed every 4 d (2 month lifespan)
• once infected pass virus in saliva

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African Horse Sickness

• endemic in Africa (outbreaks in Spain, Portugal
  1980s)
• gt75 mortality (horses)
• with VEE, most important, lethal viral disease
  of horses
• cardiac/respiratory disease - death
  within 1 week
• horse sickness fever - mild zebra,
  donkeys (maintenance hosts)
• fever swelling forebody, coughing
• transmitted by midge (culicoides) vectors
• control vector control, quarantine, vaccination

Notifiable disease