Lumpy Skin Disease Virus with Four Knocked Out Genes Was Attenuated In Vivo and Protects Cattle from Infection.

Vaccination with live attenuated vaccines is a key element in the prevention of lumpy skin disease. The mechanism of virus attenuation by long-term passaging in sensitive systems remains unclear. Targeted inactivation of virulence genes is the most promising way to obtain attenuated viruses. Four virulence genes in the genome of the lumpy skin disease virus (LSDV) Dermatitis nodulares/2016/Atyrau/KZ were sequentially knocked out by homologous recombination under conditions of temporary dominant selection. The recombinant LSDV Atyrau-5BJN(IL18) with a knockout of the LSDV005, LSDV008, LSDV066 and LSDV142 genes remained genetically stable for ten passages and efficiently replicated in cells of lamb testicles, saiga kidney and bovine kidney. In vivo experiments with cattle have shown that injection of the LSDV Atyrau-5BJN(IL18) at a high dose does not cause disease in animals or other deviations from the physiological norm. Immunization of cattle with the LSDV Atyrau-5BJN(IL18) induced the production of virus-neutralizing antibodies in titers of 4-5 log2. The challenge did not cause disease in immunized animals. The knockout of four virulence genes resulted in attenuation of the virulent LSDV without loss of immunogenicity. The recombinant LSDV Atyrau-5BJN(IL18) is safe for clinical use, immunogenic and protects animals from infection with the virulent LSDV.