Orthopoxvirus genes for Kelch-like proteins: III. Construction of Mousepox (ectromelia) virus variants with targeted gene deletions

The mousepox (ectromelia) virus genome contains four genes encoding kelch-like proteins EVM018, EVM027, EVM150, and EVM167. A complete set of insertion plasmids was constructed to produce recombinant ectromelia viruses with targeted deletions of one to four genes of the kelch family, both individual (single mutants) and combined (double, triple, and quadruple mutants). It was shown that deletions EVM018, EVM027, or EVM167 resulted in a reduction of the 50% lethal dose (LD 50) in outbred white mice infected intraperitoneally by five and more orders. Deletion of the mousepox kelch-gene EVM150 did not affect the virus virulence. Deletions of two or more kelch-genes also resulted in high attenuation levels, evidently due to the lack of EVM167, EVM018, and/or EVM027 products identified as virulence factors. The local inflammatory process assessed on the model of intradermal injection of mouse ear pinnae (vasodilatation level, hyperemia, cutaneous edema, arterial thrombosis) was significantly more pronounced for the wild type virus and virulent mutant ΔEVM150 compared to avirulent mutant ΔEVM167.