Written by: Dr. Jacquie Jacob, University of Kentucky

Infectious coryza, which is also referred to as a cold or roup, is caused by the bacterium Haemophilus paragallinarum. This disease primarily affects chickens, but quail and pheasants may also be affected.

Coryza is primarily transmitted by direct bird-to-bird contact. In addition, birds can also catch the disease by breathing airborne bacteria and consuming contaminated feed and/or water. The disease can also be introduced when infected birds are brought into the flock. Birds that have recovered from the disease remain carriers of the organism and may occasionally shed the bacteria during their lives. Birds risk exposure at poultry shows, bird swaps, and live-bird sales. Outbreaks commonly result when infected birds that are not showing any signs of the illness are brought into a healthy flock.


Typical signs of coryza include the following: 

  • Swelling around the face
  • Foul-smelling, thick and sticky discharge from the nostrils and eyes
  • Labored breathing
  • Rales

In addition, the eyelids of an infected bird can become irritated and might stick together. Diarrhea may occur. Growing birds may become stunted. Infection can decrease egg production and increase the incidence and/or severity of secondary infections. 

Mortality can be as high as 50%, but 20% is more common. The disease can last as little as a few days or as long as a few months, particularly when secondary infections occur.


Because coryza is caused by bacteria, antibiotics can be used to treat a flock. It is important to follow the labels on any medication. Although antibiotics can be effective in reducing clinical signs of the disease, they do not eliminate the bacteria from carriers.


Good management, rigorous sanitation, and a comprehensive biosecurity plan are the best ways to avoid infectious coryza. Most outbreaks occur as a result of mixing flocks. Vaccines are available, but multiple vaccinations are required to be effective. When bringing in replacement birds on a farm that has had infectious coryza, it is recommended that all the birds be vaccinated.


Overview of Infectious Coryza in chickens. Merck Veterinary Manual.