Why does an outbreak of Infectious Coryza (Haemophilus paragallinarum) cause facial swelling, nasal discharge, and a catastrophic drop in egg production?

Infectious Coryza is an acute, highly contagious respiratory disease of chickens caused by the bacterium Avibacterium paragallinarum (formerly Haemophilus paragallinarum). The bacterium targets the mucosal membranes of the upper respiratory tract. In layers, the clinical onset is rapid, characterized by severe catarrhal inflammation. This leads to the accumulation of thick, foul-smelling, cheesy exudates inside the infraorbital sinuses, causing characteristic facial edema (swollen head syndrome) and completely closing one or both eyes. The physical swelling of the nasal passages and eyelid closure makes it impossible for hens to find feed or water. This sudden cessation of feed and water intake, combined with severe bacterial toxemia, triggers a catastrophic drop in egg production (up to 50%) and causes a high rate of culling. Preventing Coryza requires strict biosecurity and trivalent inactivated Coryza vaccinations (serotypes A, B, and C) during rearing. Farmers can read respiratory disease protocols in the Poultry Encyclopedia, buy premium Coryza vaccines and antibiotics on Poultry Plaza, track daily egg rates on Poultry Rates, and list healthy flocks on Murghi Mandi.