Picornaviridae, Calciviridae, Nodaviridae Flashcards
Picornaviridae
- positive sense ssRNA’
- non-enveloped; stable in environment
- icosahedral
FMDV
Apthovirus of Picornaviridae
- high contagious disease of cloven foot animals
- fever and vesicle fomration on epithelial surfaces; mouth, muzzle, teat, interdigital space and coronary band
Swine vesicular disease
- Enterovirus of picornaviridae
- exotic to AUS
- lesions look same as FMDV
- ELISA used to diagnose
Teschovirus
Picornivaridae that causes SMEDI
Tremovirus: Avian encephalomyelitis virus
- chicken
- virus shed in faeces
- vertical transmission
Most picornaviruses have
high morbidity & low mortality
Transmission of picornaviruses
- contagious
- direct contact; abrasions to skin and mucosal surfaces aids entry
- indirect from contaminated env or fomites
- biting arthropods (mechanical vectors)
- aerosols
- ingestions
- insemination/sexua
Pathogenesis of picornaviruses
- viral RNA enters cell through membrane channel
- Rapid replication in cytoplasm
- Cellular ‘shutdown’ occurs; cellular protein synthesis declines
- Viral release when cell lyses- cytolytic
- Viraemia and tissue tropism
FMD
- affects wide variety of cloven foot animals; not horses
- large volumes produced in superficial lesion facilitating transmission
FMD virus can persist in
cats, dogs, humans, rodents but don’t cause disease- act as vectors
- migratory birds can facilitate long range movement
- humans can disseminate virus
Properties of FMDV
- tendency to mutate (difficult to control by vaccination)
- moderately stable in environment
- survives long periods in animal secretions and products
- epitheliotropic
Transmission of FMDV
- low mortality + high morbidity= infected animals become viral factories
- contagious
- direct contact, aerosols, sexual, abrasion, indirect- fomites, wind, dust
Pathogenesis of FMD
- Usually enters through respiratory tract w inial replication in oropharynx
- viraemia occurs
- localization in superficial epithelial cells
- malignant disease form that has high mortality in young animals; virus localizes in heart –> necrosis and death
FMDV diagnosis
- notifiable
- samples: all secretions- fluids, blood, post mortem
- ELISA for viral antigen
- cell culture for virus isolation
- RT-PCR
FMDV control
- very difficult; high contagious, multiple hosts, stable in environment, carriers and subclinical shedders, multiple antigenic types, short-term immunity
- vaccines must be serotype specific
- live attenuated vaccine is unsafe
- biosecurity, quaranting, restrict movement, hygiene, burning slaughtered animals
Caliciviridae
- small positive sense ssRNA
- non-enveloped
- icosahedral
- stable and resistant
RHDV
Calicivirus: Rabbit haemorrhagic disease virus- acute fatal disease in euro rabbits over 2 months old
Transmission of calicivirus
- ingestion or aerosol from animal secretions
- fomites
Pathogensis of calicivirus
- rapid replication in cytoplasm; cytolytic
- shut down host protein synthesis
- wide range of tissue tropism
Calicivirus causes
FCV VESV: blistering of skin and mucous membrane
FCV: pneumonia
RHDV and EBHVS: hepatitis
CCV: enteritis
Calicivirus has infidelity of RNA polymerase enzyme which results in
many mutants
- multiple strains and serotypes which makes vaccination difficult
VES
Calicivirus: Vesicular exanthema of swine
- cooking garbage before feeding to pigs
- reservoirs in marine animals
RHDV
Calicivirus: Rabbit Haemorrhagic disease virus
- high mortality
- rabbit under 2 months are resistant
- rapid onset of haemorrhage and necros in lung and liver
- faecal oral route; ~100% mortality
RHDV control and prevention
Vaccination:
- non-enveloped so humoral immunity sufficient
- killed vaccine available
- enhanced biosecuri; quarantine, isolation, ectoparasite control
Nodaviridae
- small. non-enveloped +ssRNA
Nodaviridae: Alphanodavirus
infects insects
Nodavirdae: Betanodavirus;
Infects fish
various genotypes
Nodavirdae: Viral Nervous Necrosis (VNN)
viral encephalopathy and retinopathy (VER)
- large juvenile fish
- huge problem in barramundi
Viral Nervous Necrosis
- invades proliferating neural tissue
- common in larval and juvenile fish
- subclinical in adults (carriers)
Transmission of VNN
- shed in reproductive fluid
- vertical transmission; in or on fertilised eggs
- horizontal transmission; fish to fish, water, aerosols, pond to pond
Treatment and control VNN
- no known treatment
- kill all infected stock
- decontaminate
- maximise water flow rates to reduce viral conc
- optimise water quality
VNN prevention
enhanced biosecurity screen breeding stock: - RT-PCR analysis- reject any positive - don't mix batches - stress free environment - hygiene
