Picornaviridae, Calciviridae, Nodaviridae

Question 1

Picornaviridae

Answer 1

• positive sense ssRNA’
• non-enveloped; stable in environment
• icosahedral

Question 2

FMDV

Answer 2

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

Question 3

Swine vesicular disease

Answer 3

• Enterovirus of picornaviridae
• exotic to AUS
• lesions look same as FMDV
• ELISA used to diagnose

Question 4

Teschovirus

Answer 4

Picornivaridae that causes SMEDI

Question 5

Tremovirus: Avian encephalomyelitis virus

Answer 5

• chicken
• virus shed in faeces
• vertical transmission

Question 6

Most picornaviruses have

Answer 6

high morbidity & low mortality

Question 7

Transmission of picornaviruses

Answer 7

• 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

Question 8

Pathogenesis of picornaviruses

Answer 8

1. viral RNA enters cell through membrane channel
2. Rapid replication in cytoplasm
3. Cellular ‘shutdown’ occurs; cellular protein synthesis declines
4. Viral release when cell lyses- cytolytic
5. Viraemia and tissue tropism

Question 9

FMD

Answer 9

• affects wide variety of cloven foot animals; not horses

- large volumes produced in superficial lesion facilitating transmission

Question 10

FMD virus can persist in

Answer 10

cats, dogs, humans, rodents but don’t cause disease- act as vectors

• migratory birds can facilitate long range movement
• humans can disseminate virus

Question 11

Properties of FMDV

Answer 11

• tendency to mutate (difficult to control by vaccination)
• moderately stable in environment
• survives long periods in animal secretions and products
• epitheliotropic

Question 12

Transmission of FMDV

Answer 12

• low mortality + high morbidity= infected animals become viral factories
• contagious
• direct contact, aerosols, sexual, abrasion, indirect- fomites, wind, dust

Question 13

Pathogenesis of FMD

Answer 13

1. Usually enters through respiratory tract w inial replication in oropharynx
2. viraemia occurs
3. localization in superficial epithelial cells
4. malignant disease form that has high mortality in young animals; virus localizes in heart –> necrosis and death

Question 14

FMDV diagnosis

Answer 14

• notifiable
• samples: all secretions- fluids, blood, post mortem
• ELISA for viral antigen
• cell culture for virus isolation
• RT-PCR

Question 15

FMDV control

Answer 15

• 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

Question 16

Caliciviridae

Answer 16

• small positive sense ssRNA
• non-enveloped
• icosahedral
• stable and resistant

Question 17

RHDV

Answer 17

Calicivirus: Rabbit haemorrhagic disease virus- acute fatal disease in euro rabbits over 2 months old

Question 18

Transmission of calicivirus

Answer 18

• ingestion or aerosol from animal secretions

- fomites

Question 19

Pathogensis of calicivirus

Answer 19

• rapid replication in cytoplasm; cytolytic
• shut down host protein synthesis
• wide range of tissue tropism

Question 20

Calicivirus causes

Answer 20

FCV VESV: blistering of skin and mucous membrane
FCV: pneumonia
RHDV and EBHVS: hepatitis
CCV: enteritis

Question 21

Calicivirus has infidelity of RNA polymerase enzyme which results in

Answer 21

many mutants

- multiple strains and serotypes which makes vaccination difficult

Question 22

VES

Answer 22

Calicivirus: Vesicular exanthema of swine

• cooking garbage before feeding to pigs
• reservoirs in marine animals

Question 23

RHDV

Answer 23

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

Question 24

RHDV control and prevention

Answer 24

Vaccination:

• non-enveloped so humoral immunity sufficient
• killed vaccine available
• enhanced biosecuri; quarantine, isolation, ectoparasite control

Question 25

Nodaviridae

Answer 25

• small. non-enveloped +ssRNA

Question 26

Nodaviridae: Alphanodavirus

Answer 26

infects insects

Question 27

Nodavirdae: Betanodavirus;

Answer 27

Infects fish

various genotypes

Question 28

Nodavirdae: Viral Nervous Necrosis (VNN)

Answer 28

viral encephalopathy and retinopathy (VER)

• large juvenile fish
• huge problem in barramundi

Question 29

Viral Nervous Necrosis

Answer 29

• invades proliferating neural tissue
• common in larval and juvenile fish
• subclinical in adults (carriers)

Question 30

Transmission of VNN

Answer 30

• shed in reproductive fluid
• vertical transmission; in or on fertilised eggs
• horizontal transmission; fish to fish, water, aerosols, pond to pond

Question 31

Treatment and control VNN

Answer 31

• no known treatment
• kill all infected stock
• decontaminate
• maximise water flow rates to reduce viral conc
• optimise water quality

Question 32

VNN prevention

Answer 32

enhanced biosecurity
screen breeding stock:
- RT-PCR analysis- reject any positive
- don't mix batches
- stress free environment
- hygiene