Occurrence: Worldwide, but more common in tropical areas of the world and in farms with multiage pullets. Coryza means head cold.
Age of bird: Mostly 15‑30 weeks, but has been seen in broiler age birds.
Species affected: Only chickens.
Cause: Haemophilus paragallinarum is a gram‑negative, polar‑staining, non‑motile bacterium, and appears as short rods or coccobacilli.