Claim 1: Mutant has a Pestivirus Genome where the Erns Gene is mutated, wherein the Gene mutated Erns is a Chimeric Erns Gene.The Chimeric Erns Gene and consists of a 5 'and 3' part, in which the 5 '- represents 60 95% of the Chimeric Erns Gene and the 3' represents the rest of the Erns Gene ChimericAnd where that Party 5 'consists of a portion of a Pestivirus Erns Gene is genetically distant from the Pestivirus MutantAnd where that part 3 'consists of the corresponding part of a Pestivirus Erns Gene of a Mutant which is genetically close to the pestiviruses.Claim 8: Method for the Construction of a Pestivirus Mutant according to any one of claims 1 - 7Said method includes the gene mutation of a Pestivirus Erns Gene in a Genome, Chimeric Erns as defined in claim 1.Claim 10: vaccine for Animals, which comprises a Pestivirus Mutant according to any one of claims 1 - 7, or a host Cell according to claim 9Or any combination thereof, and a pharmaceutically acceptable Carrier.Claim 20: diagnostic test kit comprising a Pestivirus Mutant according to any one of claims 1 - 7Or a chimerical Pestivirus Erns Protein expressed by the Mutant.Claim 21: a method for Controlling a Pestivirus infection in a population of animals of the order Artiodactyla,By the combined use of a vaccine according to claim 10 and a diagnostic test kit according to claim 20.Reivindicación 1: Pestivirus mutante que tiene un genoma en donde el gen Erns está mutado, caracterizado porque el gen Erns mutado es un gen Erns quimérico, y el gen Erns quimérico se compone de una parte 5’ y una parte 3’, en donde la parte 5’ representa 60 - 95% del gen Erns quimérico, y la parte 3’ representa el resto del gen Erns quimérico, y en donde dicha parte 5’ se compone de la parte correspondiente de un gen Erns de un Pestivirus que es genéticamente distante del Pestivirus mutante, y en donde dicha parte 3’ se compone de la parte correspondiente de un gen Erns de un Pestivirus que es genéticamente cercano al Pestivirus mu
