The pathogenesis of African swine fever in the resistant bushpig.

Bushpigs and warthogs are natural reservoir hosts of African swine fever virus (ASFV) in the wild, showing no clinical signs of disease when infected with the same highly virulent isolates of ASFV that induce rapid, haemorrhagic death in domestic pigs. In contrast to domestic pigs, infection of bushpigs with Malawi isolate results in low levels of virus replication and lymphocyte apoptosis within the spleen, and a relatively low spread of virus to other lymphoid tissues. However, at 10 days post-infection, a high degree of apoptosis was seen in B lymphocytes of the B cell follicles in bushpig lymph nodes. Virus infected cells were present amongst the apoptotic B cells of these follicles, suggesting that indirect factors released from ASFV infected macrophages signal surrounding lymphocytes to enter apoptosis. The susceptibility/resistance of domestic pigs/bushpigs to ASFV may serve as a unique veterinary model for the recently emerging haemorrhagic disease of man.