African swine fever is a highly contagious hemorrhagic disease of pigs that produces a wide range of clinical signs and lesions that closely resemble those of classical swine fever, according to the Merck Veterinary Manual.
ASFV is a large, enveloped, double-stranded DNA virus that replicates primarily in cells of the mononuclear phagocytic system. It is currently classified as the only member of a family called African swine fever–like viruses (Asfarviridae).
Peracute, acute, subacute, and chronic forms of ASF occur, and mortality rates vary from zero to 100%, depending on the virulence of the virus with which pigs are infected. Acute disease is characterized by a short incubation period of three to seven days, followed by high fever (up to 42 C) and death in five to 10 days. The least variable clinical signs are loss of appetite, depression, and recumbency; other signs include hyperemia of the skin of the ears, abdomen, and legs; respiratory distress; vomiting; bleeding from the nose or rectum; and sometimes diarrhea. Abortion is sometimes the first event seen in an outbreak. The severity and distribution of the lesions also vary according to virulence of the virus. Hemorrhages occur predominantly in lymph nodes, kidneys (almost invariably as petechiae), and heart; hemorrhages in other organs are variable in incidence and distribution.