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Clinical Diagnosis
After an incubation period of 5-10 days, ASF infection can be manifest in different forms:
Peracute:
Infection with highly virulent virus strains can result in high moratality within a few days.
Acute:
Typical symptomas are fever, loss of appetite (anorexia), inactivity, areas of red or blue skin discoloration, diarrhoea, vomiting, coughing, breathing difficulty and abortion may also occur. In pigs showing this form of infection, very high mortality is observed and most affected pigs will die withing a few days.
Subacute:
Infection with virus strains of moderate virulence causes mild disease and may result in aborts. Recovery is observed, however mortality still ranges from 30-70%. Affected pigs are only mildly ill, but sows may abort. Recovered pigs can still be excreting the virus up to six weeks after infection.
Chronic
Chronic infection results in wasting with occasional episodes of fever and necrotic patches of skin or chronic skin ulcers may be present. Pigs chronically infected with ASF are vulnerable to secondary infections, such as pneumonia and lameness (arthritis). Mortality is less than 30%.
Autopsy findings
External: Blood splashes (ecchymoses) in the skin of the legs or abdomen
Internal: typically, petechial haemorrahges are seen on kidneys, the mucous membranes of the larynx and bladder and on visceral surfaces of organs.
Also observed are enlarged lymph nodes and haemorrhages may be seen in the gastrohepatic and renal lymph nodes.
The spleen is often enlarged and there can be excess fluid in the abdominal, pleural and pericardial cavities. Oedema of the gall bladder and mesentery of the colon is also typical for ASF. In chronic cases, lungs may show focal lesions of caseous necrosis and even mineralisation.
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