36. African swine fever.

Question 1

Definition?

Answer 1

NOTIFIABLE DISEASE!

Definition:

• Usually acute viral disease of domestic swine and wild boar with fever,
• general symptoms,
• extensive haemorrhages and high mortality

Question 2

Occurrence and cause?

Answer 2

Occurrence:

• Southern part of Africa (1921),
• Kenya, Montgomery, Europe Portugal (1957), again in 1959 ʹ
• stayed in soft ticks, Spain (ticks: until 1990)
• America (1970s), Sardinia endemic, Hungary (2018)
• Ticks as biological vectors (virus can replicate in soft ticks and transmit)

Question 3

Ethiology?

Answer 3

Etiology:

• Asfarviridae family, Asfivirus genus, African swine fever virus
• 200 nm, enveloped (but still very resistant), icosahedral, linear dsDNA, 150 kbp, 1 serotype,
• virulence variants (genetically different)
• Arbovirus: present in Ornithodorus species, spread by tick and replicate in tick
• Also direct contact route (via saliva)
• There is no virus neutralization (once infected, become persistant infection, lifelong shedding,
• survival varies), hemabsorption (in hemagglutination test will always be negative - need to cell
• culture: RBC will be absorbed by infected cells)
• Susceptibility: swine, wild boar, African pig species
• Highly resistant (survive in environment for 100-200 days, years long in freezer - frozen meat, 60C
• for 20 min)
• Disinfection with 2% NaOH, 0.3% formalin, hypochlorite 30 min, iodine

Question 4

Epidemiology?

Answer 4

Epidemiology:

• Endemic areas: wartgot, bush pig, giant forest hog, recovered pigs (survived pigs shedding virus),
• ticks
• Europe, America: live pig, pork, (ticks)

Question 5

Pathogenesis?

Answer 5

Pathogenesis:

• infection PO, tick bites > primary replication (tonsils, LN) > viremia for months > spleen,
• LN, bone marrow, blood vessels endothel (hemorrhages) > replication (monocyte, macrophage,
• endothel, hepatocyte, tubular epithel, granulocyte, NOT in lymphocytes)
• Shedding via saliva, nasal discharges, can sheds 48 hr before clinical symptoms
• No virus neutralization (intensive antibody production, but antibodies cannot neutralize virus),
• cytoplasma membrane of macrophages is taken (virus hide/mimic itself with macrophages,
• immunity cannot detect)
• Immune complexes: virus release proteins => causing immunosuppression
• TYPE III THREE HYPERSENSITIVITY

Question 6

High, moderate mild?

Answer 6

Question 7

Clinical signs?

Answer 7

Clinical signs:

• incubation is 1 week
• 40-41C fever, transient anorexia, abortion in ALL virulence variants
• Clinical signs are influenced by virulence of strains
• Wild boar: milder signs, can be chronic form
• Hemorrhages on skin (large areas) with necrotic area, nasal discharges, cyanotic edges on ear

Question 8

Pathology?

Answer 8

Pathology:

• Acute:
• hyperemia,
• petechial hemorrhages everywhere, black LN, pulmonary edema,
• enlarged spleen (characteristic, 6X larger, black)
• Chronic:
• spleen, lymphoid hyperplasia,
• fibrin-rich fluid (pericardium, thorax, abdominal
• cavity),
• pneumonia, skin necrcosis

Question 9

Diagnosis and differential diagnosis?

Answer 9

Diagnosis:

• epidemiology, clinical signs, PM lesions
• Detection of virus: PCR (nucleic acid detection), IF, hemabsorption, virus isolation
• Detection of antibodies: ELISA, western bot
• Animal infection
• Differential diagnosis:

1. classical swine fever (clinical signs and pathology is very similar, differentiate by the 4 pigs test- vaccinated and infect (if 2 were vaccinated against classical swine fever but all died = infection was African swine fever),
2. PDNS,
3. acute swine paratyphoid,
4. erysipelas (Diamond Skin),
5. aujeszky disease

Question 10

Prevention, control?

Answer 10

Prevention, control:

• veterinary administration rules - its a notifiable disease
• Epidemiological measures, tick control
• No vaccine (no antibodies production
• In disease free countries: stamping out of the infected herds, disinfection, leave empty for 1 month
• before repopulation, movement restriction for 1 month after repopulation, serological control