Swine Fever Flashcards
What is Pestivirus C?
Classical Swine Fever
What are the virological features of CSFV?
Single stranded +ve sense RNA genome.
* Genomic RNA is infectious, serves as mRNA too.
* Genome approx. 12kb.
* Replicates in the cytoplasm.
What is the genome organisation of pestivirus?
- 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.
What test can detect pestiviruses?
ELISA test
What is the virus inactivated by?
- Detergents and organic solvents
- Low and high pH
- High temperatures
- UV light
What are the most favourable conditions for the virus to survive in?
- Meat- Cool, moist, protein-rich
- In the environment
- Frozen semen
How can classical swine fever be transmissed directly?
- Pig to pig contact
- Oral/ Nasal secretions
- Faeces/ Urine
- Blood
- Semen
- Transplacental
- Contact with wild boar
What is the impact of classical swine fever?
- 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
What are the early clinical signs of clinical swine fever?
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
What are the clinical signs of an established clinical swine fever outbreak?
- gaunt
- hollow-flanked
- posterior paresis
- reddening of the skin
- purplish discolouration ober the abdomen
*
What is the outcome of high virulence?
- Acute disease
- High mortality
- the outcome is generally dependent on host factors
What is the effect of moderate/ low virulence?
- sub-acute or chronic disease
- prolonged incubation
- lower mortality
- outcome can be influenced by host factors
What does clinical swine fever look like in post mortem?
- 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
What vaccine would you use in farmed pigs?
- Live vaccines are used in endemic areas, eg in eastern european countries
What areas do not use live vaccines?
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
How would you control CSF in wild boar?
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
What are the virological features of ASFV?
- Family is asfarviridae
- Genus is Asfivirus
- Group 1- Baltimore
- Double stranded DNA genome linear
- Structure- icosahedral capsid with inner and outer envelopes
What is the genome organisation of ASFV?
- 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
How is ASFV transmissed?
- 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
What are the three cycles of ASF transmission?
- Sylvatic cycle in africa (warthogs and bushpigs)
- domestic cycle
- sylvatic cycle in eurasia (wild boar)
What is the distribution of ASF?
- has 23 different genotypes
- 22 are in eastern and southern africa
- one genotype in europe
What is the pathogenesis of ASF?
- 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
What are the clinical signs of peracute/ highly virulent ASF?
- Sudden death with few or no signs
- highly virulent strain
- pigs becomd depressed, stop eating, huddle together
What are the signs of acute/ highly virulent ASF?
- 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
Where was ASF first initially reported?
1921 in Kenya
by 2007 all countries except sardinia and africa were declared ASF free
How have they controlled ASF in belgium?
- 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
What are some of the differential diagnosis for ASF?
- Salmonella
- Warfarin posioning
- Swine influenza
