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Picorna and Caliciviruses
October 14, 2009
Viruses with +ve RNA genomes
Aphtho
Picornaviridae
Caliciviridae
Coronaviridae
Arteriviridae
Flaviviridae
Togaviridae
Entero
Rhino
Cardio
Hepato
feline calicivirus
coronaviruses
equine arterivirus
pestiviruses (BVD)
equine encephalitis viruses
Picornaviruses
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“pico” - small
“rna” - RNA
single stranded, positive RNA
unenveloped, relatively stable
a hundred days of foot and mouth
BBC
Foot and mouth disease
• highly contagious disease of domestic and
wild ruminants and pigs.
• systemic disease with high fever, vesicles
on epithelial surfaces
• not usually fatal in adults but causes
economic losses (trade implications)
• can be fatal in young animals - myocarditis
Susceptibility to inactivation
• pH
– stable between pH 7 and 9
– inactivated by:
• 5% acetic acid or other acids
• 1-2% sodium hydroxide or other alkalis
• phenolic and quarternary ammonium compounds - not effective
• oxidizing agents (bleach) effective when environment not
contaminated with organic substances. Detergents increase
effectiveness
• heat
– in suspension 80o for 1 hr, 50o for 2 days, 37o for seven days
– stable when associated with dried organic matter (see Dekker,
1998, Vet. Rec 143:168)
CFIA recommendations for
inactivation
• 50% solution of vinegar in water - 30 min
• sodium carbonate, 100 gm/L - 30 min
• citric acid powder - 2 gm/L - 30 min
Serotypes
• 7 serotypes - O, A, C, South African territories
(SAT)-1, SAT-2, SAT-3, Asia
• At least 60 subtypes
from:
Grubman and
Baxt, 2004
Susceptible species
• domestic ruminants (cattle, buffalo, sheep,
goats, camelids*)
• wild or exotic ruminants (african buffalo,
various antelope and deer species)
• others (pigs, rabbits, mice, guinea pigs,
chickens, elephants, humans)
• horses are resistant
Different effects on susceptible
species
• pigs (amplifying hosts) - secrete large amounts of
virus in breath, air borne spread
• cattle (sentinel hosts) - highly sensitive to
infection by respiratory route
• sheep (maintenance hosts) - mild-asymptomatic
disease, can spread through flocks before
detection
recovery
Pathogenesis
(most animals
but effects can
persist)
infection
(inhalation,
ingestion,
AI)
incubation period
(1-21 days, usually 3-5 in cattle, 4-9 in pigs)
clinical signs
(variable)
persistence
infectious dose =
< 10 particles
virus shedding
(begins 1-4 days before
clinical signs appear)
(months to years
in partially
immune animals,
life time in some
species)
death
(myocarditis
in young
animals)
Clinical signs
high fever 40-41o
•fluid filled vesicles - on
mucosa and face, feet,
hairless areas - rupture
to form ulcers
lameness - ulcers
on feet
salivation,
anorexia - lesions
in mouth
Infection of heart muscle
young animals (up to 6 months of age in cattle)
Epidemiology
• Factors that allow rapid spread and persistence in a
population
– antigenic variation (7 serotypes with no cross protection
and many antigenic variants with limited cross
reactivity)
– large host-range (including wild-life)
– low infectious dose (<10 particles)
– large amounts of virus before clinical signs develop
– no clinical signs in some species (sheep, cattle) allows
spread
– persistent infection in partially immune animals
– hardy virus (many routes of spread, airborne)
Prevention
• In countries with endemic FMD
– vaccination
– vaccination and slaughter
• FMD free countries
– prevent introduction
– in face of outbreak
• test and slaughter
• ring-vaccination and slaughter
• ring-vaccination and slaughter only sick animals
Problems with vaccination
• no cross protection if wrong serotype
• short-lived immunity
• partial protection if variant
– does not prevent infection
– persistent infection
• cannot distinguish between vaccinated and
infected animals
• detection easier if no vaccination
Regaining FMD-free status
• “stamping out” without vaccination - 3 months
after last case
• slaughter and ring vaccination - 3 months after
last slaughter of last vaccinated animal
• if all vaccinated animals are not slaughtered – FMD free status with vaccination
• 12 months after last case
– to regain FMD free without vaccination
• no cases for 12 months after last vaccination
• no importation of vaccinated animals
New Developments
• Techniques that distinguish between
vaccinated and infected animals
Diagnosis
• clinical signs - can be confused with other
vesicular diseases
• laboratory
– sample collection
• vesicle fluid, skin at edge of ruptured vesicle, excretions and
secretions
• inoculated onto susceptible cells
• if cpe - confirm FMD and serotype by capture ELISA
• if no cpe - 2 “blind” passages
– PCR
Idiopathic vesicular disease in swine in Manitoba
Tim Pasma, Suzanne Davidson, Sheryl Shaw, 2008, CVJ
49:84-85
Tim Pasma, 2008, CVJ 49:84-85
Some viruses that cause vesicular
disease in swine
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Foot and mouth disease (reportable)
Swine vesicular disease (reportable)
Vesicular stomatitis (reportable)
Vesicular exanthema (not in N
America)
• Porcine parvovirus
• Porcine enterovirus
Calicivirus
Caliciviruses
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vesicular exanthema of swine
San Miguel sea lion virus
feline calicivirus
rabbit haemorrhagic virus
bovine and porcine enteric caliciviruses
chicken calicivirus
feline calicivirus
Fe calicivirus in exotic cats