Systematic Veterinary Virology

SYMPTOMS

• The infection is exhibited as peracute, acute, subacute or chronic forms. Clinical signs appear approximately 5–15 days after natural infection with ASF virus. The first sign is usually the development of a high fever (41-42C°), manifested by depression, loss of appetite, seeking shade, huddling together, rapid breathing and, in white-skinned pigs, flushing of the skin, particularly the extremities and the underparts. Pigs often develop a swaying gait, with the hind legs appearing weak. Thick whitish discharges from the nose and eyes are sometimes seen.
• Difficult breathing is usual and foam, often blood-tinged, may appear at the nostrils. Pigs may show signs of abdominal pain. Vomiting is common. Some pigs become constipated, while others may develop a bloody diarrhoea. Sows may abort at all stages of pregnancy. The flushing of the skin in white-skinned pigs may deepen to a bluish-purple colour and there may be bleeding under the skin. Mucous membranes are red and congested. A coma due either to haemorrhagic shock or to excessive fluid in the lungs may develop before death, which usually occurs from one to seven days after development of clinical signs. Pigs that survive for a few days may develop nervous signs.
• Pigs that survive the acute stage of the disease may progress to the subacute or chronic stage. Subacute disease is characterized by fluctuating fever, accompanied by depression and loss of appetite. Walking may appear painful, with swelling of the joints. There may be signs of pneumonia. Death can be due to heart failure. Before death, signs of heart failure such as swelling of the throat may occur. Chronically sick pigs generally become emaciated, with long, dull hair and may have ulcerative sores over bony points. The pigs may walk stiffly due to arthritis. The survival period of such pigs varies from a few weeks to months.