Chicken anemia virus/physiology; Genetic Drift; Infectious bronchitis virus/physiology; Infectious bursal disease virus/physiology; Poultry Diseases/virology; Virus Replication; Animals; Antibodies, Viral/blood; Birnaviridae Infections/immunology; Birnaviridae Infections/veterinary; Birnaviridae Infections/virology; Chicken anemia virus/immunology; Chickens; Circoviridae Infections/immunology; Circoviridae Infections/prevention & control; Circoviridae Infections/veterinary; Circoviridae Infections/virology; Coronavirus Infections/immunology; Coronavirus Infections/veterinary; Coronavirus Infections/virology; Genetic Variation; Genotype; Host-Pathogen Interactions; Immunocompromised Host; Infectious bronchitis virus/genetics; Infectious bronchitis virus/isolation & purification; Infectious bursal disease virus/immunology; Poultry Diseases/immunology; Poultry Diseases/prevention & control; RNA, Viral/genetics; Selection, Genetic; Sequence Analysis, DNA; Specific Pathogen-Free Organisms; Spike Glycoprotein, Coronavirus/genetics; Tears/virology; Viral Vaccines/immunology