Animals Antiviral Agents Article Cell Culture Techniques Defective Viruses Dogs Influenza A virus MDCK cell line Madin Darby Canine Kidney Cells Models, Biological Orthomyxoviridae Infections RNA directed RNA polymerase RNA, Viral Virus Replication animal animal cell animal cell culture antiviral therapy antivirus agent apoptosis biological model cell culture technique centrifugation chemistry coinfection controlled study defective virus dog dynamics flow cytometry