Serial PassageVirus CultivationDefective VirusesVirus ReplicationVirulenceViral InterferenceMultiple Sclerosis, Chronic ProgressiveMutationCytopathogenic Effect, ViralGenome, ViralBase SequenceRNA, ViralMolecular Sequence DataViral Plaque AssayGenes, vpuGlutamate-Cysteine LigaseAdaptation, BiologicalHelper VirusesNeoplasm TransplantationCulture MediaCricetinaeGenetic VariationDNA, ViralFoot-and-Mouth Disease VirusPhenotypeReassortant VirusesVero CellsHepatovirusCulture TechniquesMicrobial Sensitivity TestsSerial LearningHaplorhiniViral ProteinsDrug Resistance, MicrobialTime FactorsRepliconOrthomyxoviridaeViral VaccinesFoot-and-Mouth DiseaseTransplantation, HeterologousVaccines, AttenuatedAdaptation, PhysiologicalAphthovirusAnti-Bacterial AgentsPrPSc ProteinsPoliovirusAmino Acid SequenceGenes, ViralMesocricetusAntigens, ViralDrug Resistance, BacterialRecombination, GeneticAmino Acid SubstitutionSelection, GeneticScrapieSequence Analysis, DNACattleSpecies SpecificityDogsKidneyPinealomaDrug Resistance, ViralDNA PrimersTibetNeoplasms, ExperimentalNucleopolyhedrovirusHIV-1RNA, Ribosomal, 23SPolymerase Chain ReactionDisease Models, AnimalSimian virus 40Cell DivisionMicroscopy, ElectronCloning, MolecularStaphylococcus aureusViral Envelope ProteinsBrainL Cells (Cell Line)Genetic VectorsFibroblastsVirionVirus AssemblyMutagenesisSimian immunodeficiency virusSwineGenetic EngineeringFluorescent Antibody TechniqueMice, NudeTemperatureSequence DeletionReverse Transcriptase Polymerase Chain ReactionFluoroquinolonesSheepMice, Inbred BALB CDNA Restriction EnzymesAnti-Infective AgentsReverse Transcriptase InhibitorsHeLa CellsAntibodies, ViralBiological Evolution