Swine Fever

Question 1

What is Pestivirus C?

Answer 1

Classical Swine Fever

Question 2

What are the virological features of CSFV?

Answer 2

Single stranded +ve sense RNA genome.
* Genomic RNA is infectious, serves as mRNA too.
* Genome approx. 12kb.
* Replicates in the cytoplasm.

Question 3

What is the genome organisation of pestivirus?

Answer 3

• Genome 11.3-13kb.
• Single ORF about 11.7kb.
• Polyprotein is made and cleaved:
• No sub-genomic mRNA made.
• Both cellular and viral proteases process
  the polyprotein.

Question 4

What test can detect pestiviruses?

Answer 4

ELISA test

Question 5

What is the virus inactivated by?

Answer 5

• Detergents and organic solvents
• Low and high pH
• High temperatures
• UV light

Question 6

What are the most favourable conditions for the virus to survive in?

Answer 6

• Meat- Cool, moist, protein-rich
• In the environment
• Frozen semen

Question 7

How can classical swine fever be transmissed directly?

Answer 7

• Pig to pig contact
• Oral/ Nasal secretions
• Faeces/ Urine
• Blood
• Semen
• Transplacental
• Contact with wild boar

Question 8

What is the impact of classical swine fever?

Answer 8

• Notifiable disease
• UK last outbreak in 2000
• by the time CSF is suspected and diagnosed pig movement will have spread the virus across the UK

Question 9

What are the early clinical signs of clinical swine fever?

Answer 9

Only a few pigs are affected
* drowsy, less active
* straight backs
* reduced appetite, marked anorexia
* drop in leukocyte count
* eyes have marked discharge and conjungtivitis

Question 10

What are the clinical signs of an established clinical swine fever outbreak?

Answer 10

• gaunt
• hollow-flanked
• posterior paresis
• reddening of the skin
• purplish discolouration ober the abdomen
  *

Question 11

What is the outcome of high virulence?

Answer 11

• Acute disease
• High mortality
• the outcome is generally dependent on host factors

Question 12

What is the effect of moderate/ low virulence?

Answer 12

• sub-acute or chronic disease
• prolonged incubation
• lower mortality
• outcome can be influenced by host factors

Question 13

What does clinical swine fever look like in post mortem?

Answer 13

• Multiple haemorrhages of various sizes (e.g haemorrhage of lymph nodes)
• Lymph nodes are swollen
• Petechiae on kidneys (urinary bladder, larynx, epiglottis, heart, intestinal mucosa,)
• infarction of the spleen

Question 14

What vaccine would you use in farmed pigs?

Answer 14

• Live vaccines are used in endemic areas, eg in eastern european countries

Question 15

What areas do not use live vaccines?

Answer 15

CSF free areas- e.g parts of the UK
* Risk of vaccine break through
* it complicates detection and control of the disease if an outbreak were to occur

Question 16

How would you control CSF in wild boar?

Answer 16

Oral vaccination- has been succesful in europe in reducing prevalence but it is important that you use the correct bait for target animals
* also important that bait is timed with local food availability

Question 17

What are the virological features of ASFV?

Answer 17

• Family is asfarviridae
• Genus is Asfivirus
• Group 1- Baltimore
• Double stranded DNA genome linear
• Structure- icosahedral capsid with inner and outer envelopes

Question 18

What is the genome organisation of ASFV?

Answer 18

• replicates in the cytoplasm, but requires viral DNA replication particularly in the early stages
• it encodes for many proteins which combat the host cell anti-viral response

Question 19

How is ASFV transmissed?

Answer 19

• The main infection route is oro-nasal (direct or indirect pig feeding)
• It is the only DNA virus that is transmissed by arthropods (soft ticks, ornithodoros erraticus and moubata)
• can also be transmissed via semen

Question 20

What are the three cycles of ASF transmission?

Answer 20

• Sylvatic cycle in africa (warthogs and bushpigs)
• domestic cycle
• sylvatic cycle in eurasia (wild boar)

Question 21

What is the distribution of ASF?

Answer 21

• has 23 different genotypes
• 22 are in eastern and southern africa
• one genotype in europe

Question 22

What is the pathogenesis of ASF?

Answer 22

• enters via the oral-nasal route
• primary replication is in the tonsils and lymph nodes
• primary viremia then follows- it is a virus assocaited with erythrocytes and leukocytes
• generalised infection- has a high virus titre, all infections carry high amounts of the virus
• haemorrhages occur widely
• marked petechaition

Question 23

What are the clinical signs of peracute/ highly virulent ASF?

Answer 23

• Sudden death with few or no signs
• highly virulent strain
• pigs becomd depressed, stop eating, huddle together

Question 24

What are the signs of acute/ highly virulent ASF?

Answer 24

• Fever, depression, loss of appetite, weak hind legs
• vomiting diarrhoea
• nose and eye discharge, mucus membranes are red and congested
• abortion may occur in pregnant sows
• any survivor is a virus carrier for life

Question 25

Where was ASF first initially reported?

Answer 25

1921 in Kenya
by 2007 all countries except sardinia and africa were declared ASF free

Question 26

How have they controlled ASF in belgium?

Answer 26

• Preventative cull of 5000 domestic pigs
• ban of hunting and feeding wild boar
• testing on wild boar found dead
• control on access to the forest
• building network of fences within the infected zone

Question 27

What are some of the differential diagnosis for ASF?

Answer 27

• Salmonella
• Warfarin posioning
• Swine influenza