Vectors for the genetic manipulation of African swine fever virus.

Plasmid vectors designed to facilitate the genetic manipulation of African swine fever virus (ASFV) are described. Our results demonstrate that the beta-glucuronidase enzyme (GUS) can be used to follow gene expression in ASFV-infected cells. Infectious plaques formed by ASFV expressing GUS are visually detectable, thus providing a simple and highly sensitive method for the selection of ASFV recombinants. These and previous results have allowed us to construct two chimeric gene cassettes that constitute the basic tools for the generation of vectors to carry out the deletion of multiple target sequences from the ASFV genome. These cassettes, formed by: (a) a virus promoter; (b) the coding sequence of a reporter gene, either Lac Z or gusA; and (c) a strong signal for the 3' end formation of ASFV mRNAs, can be easily isolated by endonuclease restriction from their corresponding plasmid vectors. A general insertion/coexpression plasmid vector, pEPV2, has also been constructed. pEPV2 facilitates the insertion of foreign genes, together with the Lac Z reporter, into the thymidine kinase locus of ASFV. The functionality of pEPV2 has been tested by generating a recombinant ASFV expressing the luciferase gene. The vectors presented in this report constitute the first reported set of tools for the genetic manipulation of ASFV.