Pathogenesis and clinical signs in domestic pigs:

- Virus infects via the upper respiratory tract, or skin from ticks, and enters the bloodstream in monocytes to reach the viscera and bone marrow in a few days. The virus binds to rbcs to cause haemolysis. The virus also infects helper T cells such that cytokines for B-cell differentiation are missing and the B cells undergo apoptosis.

- Acute viruses (Africa):

-Clinical signs are respiratory discharges and diarrhoea. Reddened areas sometimes appear on the skin. Death is typically within 7 days of symptoms.

- At post mortem, large internal widespread haemorrhages.

- Subacute viruses (Europe):

Haemorrhages and splenomegaly are less marked than with the acute viruses and petechial haemorrhages may be seen under the kidney capsule. Mortality of up to 30-70%. Some survivors become emaciated with skin ulcers and joint swellings. Other survivors become clinically normal but still act as carriers for several months.