History, Etiology, transmission, pathogenesis, clinical signs, diagnosis, prevention and control

1. Faculty of Veterinary Medicine & Animal
Husbandry
Somali National University
Mogadishu, Gaheyr Campus
Oct. 02. 2022
Viral Diseases
AFRICAN SWINE FEVER (ASF)

2. History
1921: Discovered in Kenya
Today: endemic
in most of
sub-Saharan
Africa including
the island
of Madagascar

3. 1957: First occurrence outside Africa
- Portugal
1960s:
Portugal and Spain
1970-1980s:
Spread to Europe
The Netherlands,
Italy, France, Belgium
1990s: Disease eradicated Remains
endemic on the Island of Sardinia

4. Tick Vector
1963: Virus isolated from soft
tick Ornithodoros erraticus
1971: Western Hemisphere
Cuba, the Dominican
Republic, Haiti, Brazil
Eradicated

5. 2007: Republic of Georgia
Spread in Caucasus
Region (Eurasia),
including Russia
Federation
2015:
Eastern Europe
Lithuania, Latvia,
Poland, Romania
Wild boar in Iran

6. Outbreaks
China: 2018 first time reported, domestic pigs
Belgium: Wild boars
Hungary, Estonia, Latvia, Lithuania, Russia, Poland,
Ukraine, Bulgaria, Romania

7. Uncooked/undercooked pork products fed to pigs
(imported, illegal)
Portugal , Spain (1960); Italy (1983); Belgium
(1985); Russia (2008); Romania, China (2018)
Raw pork waste/garbage at airport or shipping
ports
Lisbon (1957), Malta, Sardinia (1978), Georgia
(2007)
Movement of infected wild boars Russia (2008)

8. African swine fever is an important viral disease of
pigs that has become a serious threat to worldwide pork
production since 2007. African swine fever virus
(ASFV) usually circulates in sub-Saharan Africa, where
it is thought to have originated in wild warthogs but has
become a common virus in domesticated pigs.

9. ASF viruses range from highly pathogenic strains that may
kill nearly the entire herd to less virulent isolates that cause
a milder, nonspecific illness difficult to recognize as African
swine fever.

10. Etiology
African swine fever results from infection by African
swine fever virus (ASFV), an enveloped virus in the
genus Asfivirus and family Asfarviridae.

11. More than 20 genotypes of ASFV have been identified,
many from wildlife cycles in Africa. Some of these
viruses also occur in domesticated pigs.

12. The virus introduced in 2007 into the Caucasus belongs
to genotype II, while a virus that has been endemic in
Sardinia (Italy) since the 1960s is of genotype I.

13. Map: ASF Infection Distribution OIE: Jan-Sept 2018.
Geographic Distribution

14. Morbidity up to 100% Previously unexposed herds
Mortality varies with genotype virulence Ranges
from <5% to 100%
All ages affected
Subacute mortality = 30% to 70%
May be asymptomatic in wild pigs

15. Economic Impact
Animal health
High morbidity and mortality
Highly contagious
Import and export bans
Movement restrictions
Quarantine and depopulation
Required for eradication
1971-Cuba: 400,000 pigs
2018-Romania: over 120,000 pigs
Can become prolonged epidemic

16. Species Affected
Domestic pigs
Feral swine
Wild pigs
Eurasian wild boars
Warthogs (reservoir)
Bush pigs (reservoir)
Giant forest hogs
European boar warthog
bush pig
Domestic pig

17. Transmission
Direct contact with infected pig
Usually oronasal
All secretions/excretions, blood, tissues
Environmental contamination with products
Ingestion of contaminated
pork products
Fed to pigs – swill, waste, garbage
Carcasses

18. Fomites
Clothing, vehicles, equipment
Environmental contamination
Blood, diarrhea, feces
Vectors
Biological: Bite from soft ticks
Ornithodoros
Mechanical: Other insects
Mosquitoes, biting flies (Stomoxys)

19. Ornithodoros soft ticks
Transstadial
Transovarial
Sexual transmission
Infected for life
Colonies maintain virus for years
Tick-to-pig transmission
Important in Africa
Maintained between warthogs and tick

20. Clinical Features
Incubation period
5-21 days following direct contact
< 5 days after tick bite
Forms of disease
Peracute – sudden death
Acute
Subacute
Chronic

21. Sudden deaths with few lesions (peracute cases)
may be the first sign of an infection in some herds.
Acute cases are characterized by a high fever,
anorexia, lethargy, weakness and recumbency.
Erythema can be seen, and is most apparent in white
pigs.

22. There may also be other hemorrhagic signs, including
epistaxis and hemorrhages in the skin.
Respiratory signs (including dyspnea), nasal and
conjunctival discharges, and neurological signs have
been reported.
Pregnant animals frequently abort.

23. Subacute African swine fever is similar, but with less severe
clinical signs. Fever, thrombocytopenia and leukopenia may
be transient; however, hemorrhages can occur during the
period of thrombocytopenia. Abortions are sometimes the first
sign of an outbreak in this form. Affected pigs usually die or
recover within 3 to 4 weeks.

24. Pigs with the chronic form have nonspecific signs such as
an intermittent low fever, appetite loss and depression.
Other signs may be limited to emaciation and stunting,
but some pigs develop respiratory problems and swollen
joints. Coughing is common, and diarrhea and occasional
vomiting have been reported.

25. Pig. There is bloody, mucoid, foamy nasal discharge.

26. Pig, limbs. There is marked hyperemia of the distal limbs.

27. Pig, perineal skin. There is a large sharply demarcated zone of hyperemia.

28. Pig. There are multiple sharply demarcated foci of cutaneous hemorrhage and/or necrosis;
hemorrhagic lesions may contain dark red (necrotic) centers

29. Pig. There are multiple sharply demarcated foci of cutaneous hemorrhage and/or
necrosis; hemorrhagic lesions may contain dark red (necrotic) centers.

30. Pig, skin. Necrotic exudate is sloughing from the lesion on the left.

31. Postmortem Lesions
The gross lesions are highly variable, and are influenced by
the virulence of the isolate and the course of the disease.
Numerous organs may be affected, to varying extent, in
animals with acute or subacute African swine fever.
The carcass is often in good condition in animals that die
acutely.

32. Pig, kidney. There is moderate perirenal (retroperitoneal) edema.

33. Pig, kidney. Petechiae are disseminated throughout the cortex, and there are larger
coalescing pelvic hemorrhages.

34. Pig, kidney. Close-up of cortical petechiae.

35. Pig, kidney. There is severe disseminated cortical petechiation; the pale foci are
infarcts.

36. Pig, urinary bladder. There are disseminated mucosal petechiae.

37. Pig, heart. There is abundant straw-colored pericardial fluid (hydropericardium), and
multifocal epicardial hemorrhage.

38. Pig, heart. Subendocardial hemorrhage.

39. Pig, lung. The lung is noncollapsed and edematous; there is dorsal hemorrhage and ventral
consolidation.

40. Pig, stomach. There is "paintbrush" hemorrhage on the serosa.

41. Pig, mandibular lymph node. There is moderate peripheral (medullary) hemorrhage

42. Pig, stomach. The hepatogastric lymph node is markedly enlarged and hemorrhagic, and the
adjacent lesser omentum is edematous

43. Pig, stomach. The stomach is filled with clotted blood, and the wall is markedly
edematous.

44. Pig, spiral colon. The colon is distended with bloody contents (due to a hemorrhagic
gastric ulcer).

45. Pig, cecum. Mucosa is markedly edematous and hyperemic, and lymph nodes are hemorrhagic.

46. Zoonotic potential
There is no evidence that ASFV infects humans.
There is no public health or food safety concern.

47. Differential Diagnosis
Classical swine fever
(hog cholera)
Porcine dermatitis and
nephropathy syndrome
Erysipelas
Salmonellosis
Eperythrozoonosis
Actinobacillosis
Glasser’s disease
Aujeszky’s disease
(pseudorabies)
Thrombocytopenic purpura
Warfarin poisoning
Heavy metal toxicity

48. Sampling
Before collecting or sending any samples, the proper
authorities should be contacted.
Samples should only be sent under secure conditions and to
authorized laboratories to prevent the spread of the disease
Reportable disease.
If ASF suspected, IMMEDIATELY notify animal health
authorities

49. Virus isolation
Blood, tissues
PCR
Clinical samples, putrefied
samples, fresh tissues/blood
Tonsils for FAD
investigation
Serological
ELISA
Immunoblotting
Indirect fluorescent antibody
(IFA)
Smears, cryostat, buffy coat
Endemic regions
Diagnosis

50. No treatment available
No treatment should be attempted
No vaccine available
Depopulation
Restrictions on pig movements

51. Prevention & Control
Prevent direct transmission between infected and susceptible
Isolate ill pigs.
Prevent contact with feral or wild hogs; when possible
house pigs indoors.
Keep newly acquired pigs separate from the herd for at
least 30 days to assure health.

52. Do not feed uncooked pork products to pigs
Swill, garbage, waste
Disinfection
Vehicles, equipment, footwear, clothing
Appropriate disposal of manure and carcasses
Avoid hunting wild hogs prior to contact with
domestic pigs.
Control tick and other insect vectors
May be difficult in endemic areas

53. Quarantine of farm, Authorities notified
Movement restrictions

54. Eradication
Euthanize/depopulation of infected and in-contact animals