The non-haemadsorbing African swine fever virus isolate ASFV/NH/P68 provides a model for defining the protective anti-virus immune response

African swine fever virus ASFV/NH/P68 is a naturally occurring, non-haemads orbing and non-fatal isolate. Longitudinal clinical and immunological studi es on 31 pigs inoculated oronasally or intramuscularly with this isolate de fined two discrete groups of animals: those developing ASF chronic type les ions and those remaining asymptomatic. Animals developing lesions had virae mia and fever late after infection, NK activity levels close to that of con trol animals and high levels of anti-ASFV specific antibodies together with a marked hypergammaglobulinaemia involving IgG1, lgG2, IgM and IgA immunog lobulin isotypes. Pigs remaining asymptomatic after infection, on the other hand, did not have viraemia or fever after day 14 post-infection and had e levated Nh cell activity, but normal plasma Ig concentrations and relativel y low specific anti-virus antibody concentrations throughout the duration o f the experiments. Importantly, the latter group of pigs virus were resista nt to subsequent challenge with the highly virulent ASFV/L60 isolate and su rvived with no major changes in any of the parameters examined and referred to above. Finally, lymphoproliferative responses to the mitogens concanava lin A, phytohaemagglutinin and pokeweed mitogen were not depressed in eithe r of the two clinically defined groups of pigs. Thus further studies with t his infection model may provide new insights on mechanisms of protective im munity to ASFV.