Picorna and Caliciviruses October 14, 2009. Viruses with +ve RNA genomes Picornaviridae...
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Transcript of Picorna and Caliciviruses October 14, 2009. Viruses with +ve RNA genomes Picornaviridae...
Viruses with +ve RNA genomes
Picornaviridae
Caliciviridae
Coronaviridae
Arteriviridae
Flaviviridae
Togaviridae
feline calicivirus
equine arterivirus
pestiviruses (BVD)
coronaviruses
equine encephalitis viruses
EnteroAphtho
Rhino
HepatoCardio
Picornaviruses
• “pico” - small
• “rna” - RNA
• single stranded, positive RNA
• unenveloped, relatively stable
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
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
Pathogenesisinfection(inhalation,ingestion,AI)
incubation period(1-21 days, usually 3-5 in cattle, 4-9 in pigs)
clinical signs(variable)
recovery(most animals but effects can persist)
persistence(months to years in partially immune animals, life time in some species)
virus shedding(begins 1-4 days beforeclinical signs appear)
death(myocarditis in young animals)
infectious dose = < 10 particles
Clinical signs
•fluid filled vesicles - on mucosa and face, feet, hairless areas - rupture to form ulcers
lameness - ulcers on feet
high fever - 40-41o
salivation, anorexia - lesions in mouth
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
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 ManitobaTim Pasma, Suzanne Davidson, Sheryl Shaw, 2008, CVJ
49:84-85
Some viruses that cause vesicular disease in swine
• Foot and mouth disease (reportable)
• Swine vesicular disease (reportable)
• Vesicular stomatitis (reportable)
• Vesicular exanthema (not in N America)
• Porcine parvovirus
• Porcine enterovirus
Caliciviruses
• vesicular exanthema of swine
• San Miguel sea lion virus
• feline calicivirus
• rabbit haemorrhagic virus
• bovine and porcine enteric caliciviruses
• chicken calicivirus