The slow spread extends the period of sick birds within the flock to several weeks. The presence of other respiratory infections as mycoplasma will increase the duration and severity of illness of sick birds and impact on flock growth and production. Once a flock has been infected, it is a constant threat to other clean flocks. The nasal exudates are thick clear sticky in texture with a fetid or rotten odor. Sick birds become lethargic, will sit humped, have ruffled feathers, go off feed and water and have swollen faces.
Some birds also have sinusitis.
The facial swelling is primarily around the eye and not always involving the infra-orbital sinus. Mortality can be as high as 50 percent but usually no more than 20 percent. The course and mortality of the disease correlate with the virulence of the pathogen, treatment, and concomitant infections. In the acute stage, the principal lesions are swollen face, watery eyes, rhinitis, nasal exudates that become crusty on the beak around nostrils and cheesy in nostrils and sinuses. Eyelids stick together by the exudate or an accumulation of cheesy exudate in the conjunctival sac.