Pathogenesis of H5N6 viruses in specific pathogen-free chickens. (A) Percentage of survival of SW8 and ZH283 in chickens. (B) Comparison of two A(H5N6) influenza virus titers of wild bird origin in chickens. Groups of 12 6-week-old chickens were intranasally inoculated with 0.2 mL of 105 EID50 of SW8, ZH283, or PBS; six chickens in each group were euthanized at 3 days post-infection, and lung, kidney, spleen, cecal tonsils, bursa of Fabricius, trachea, pancreas, liver, heart, brain, duodenum, ileum, descending colon, and jejunum tissues were collected. The remaining chickens were observed for clinical signs of illness and lethality for 2 weeks. Virus titers were determined in eggs and expressed as log10 EID50/g of tissue. Data are expressed as M ± SD. Dashed black lines indicate the lower limit of detection. Differences were analyzed with a paired Student’s t-test and were considered statistically significant at ∗p < 0.05 compared to control.