Generation and Evaluation of an African Swine Fever Virus Mutant with Deletion of the CD2v and UK Genes

African swine fever (ASF) is a highly contagious and often lethal disease caused by African swine fever virus (ASFV). ASF emerged in China in August 2018 and has since rapidly spread into many areas of the country. The disease has caused a significant impact on China's pig and related industries. A safe and effective vaccine is needed to prevent and control the disease. Several gene-deleted ASFVs have been reported; however, none of them is safe enough and commercially available. In this study, we report the generation of a double gene-deleted ASFV mutant, ASFV-SY18- increment CD2v/UK, from a highly virulent field strain ASFV-SY18 isolated in China. The results showed that ASFV-SY18- increment CD2v/UK lost hemadsorption properties, and the simultaneous deletion of the two genes did not significantly affect the in vitro replication of the virus in primary porcine alveolar macrophages. Furthermore, ASFV-SY18- increment CD2v/UK was attenuated in pigs. All the ASFV-SY18- increment CD2v/UK-inoculated pigs remained healthy, and none of them developed ASF-associated clinical signs. Additionally, the ASFV-SY18- increment CD2v/UK-infected pigs developed ASFV-specific antibodies, and no virus genome was detected in blood and nasal discharges at 21 and 28 days post-inoculation. More importantly, we found that all the pigs inoculated with 10(4) TCID50 of ASFV-SY18- increment CD2v/UK were protected against the challenge with the parental ASFV-SY18. However, low-level ASFV DNA was detected in blood, nasal swabs, and lymphoid tissue after the challenge. The results demonstrate that ASFV-SY18- increment CD2v/UK is safe and able to elicit protective immune response in pigs and can be a potential vaccine candidate to control ASF.