A protective multiple gene-deleted African swine fever virus genotype II, Georgia 2007/1, expressing a modified non-haemadsorbing CD2v protein.

African swine fever virus is a complex DNA virus that causes high fatality in pigs and wild boar and has a great socio-economic impact. An attenuated genotype II strain was constructed by replacing the gene for wildtype CD2v protein with versions in which single or double amino acid substitutions were introduced to reduce or abrogate the binding to red blood cells and reduce virus persistence in blood. The mutant CD2v proteins were expressed at similar levels to the wildtype of protein on the surface of infected cells. Three recombinant viruses also had K145R, EP153R and in one virus DP148R genes deleted. Following immunisation of pigs, the virus with a single amino acid substitution in CD2v, Q96R, induced moderate levels of replication and 100% protection against virulent ASFV. Two additional recombinant viruses had two amino acid substitutions in CD2v, Q96R and K108D, and induced no binding to red blood cells . In immunised pigs, reduced levels of virus in blood and strong early ASFV specific antibody and cellular responses were detected. After challenge, 83 to 100% protection with low to moderate replication of challenge virus were observed. Reduced clinical signs post-challenge were observed in pigs immunised with the virus from which DP148R gene was deleted. Protection levels of 83 to 100% were maintained across a range of doses. Further experiments with virus GeorgiaΔDP148RΔK145RΔEP153R-CD2v_mutantQ96R/K108D, showed low levels of virus dissemination in tissue and transient clinical signs at high doses. The results support further evaluation of GeorgiaΔDP148RΔK145RΔEP153R-CD2v_mutantQ96R/K108D as a vaccine candidate.