Infectious coryza

Infectious coryza is an acute bacterial disease of the upper respiratory tract in poultry, most often chickens. It can be recognised by a swollen face and sinuses, nasal discharge and an unpleasant smell. The disease spreads quickly through a flock, and birds that survive often remain carriers for life.

It is caused by the bacterium Avibacterium paragallinarum. Chickens are most often affected, and occasionally pheasants and guinea fowl too. The first signs appear just a few days after infection, and the disease can spread through almost the whole flock in a short time.

The bacterium spreads:

• through direct contact between sick and healthy birds;
• through discharge from the nose and eyes that contaminates water and feed;
• through shared drinkers and feeders;
• by bringing in new birds that look healthy but are actually carriers.

The most common triggers of an outbreak:

• mixing birds of different ages and origins;
• an overcrowded henhouse and poor ventilation;
• damp, draughts and sudden changes in temperature;
• stress from transport, moving or other diseases.

Signs on the head and in the respiratory system:

• swelling of the face, the sinuses below the eyes and the wattles, sometimes on one side only;
• watery, later thick and foul-smelling nasal discharge;
• swollen, stuck-together eyelids and discharge from the eyes;
• sneezing, rattling breathing and difficulty breathing.

General signs:

• loss of appetite and drinking less water;
• lethargy, apathy and loss of interest in their surroundings;
• ruffled, untidy feathers;
• weight loss, especially if the illness lasts longer;
• a sudden drop in egg laying;
• occasionally diarrhoea.

The illness usually lasts two to three weeks, and longer if there are secondary infections. Deaths are generally rare, but the flock lays less and grows more slowly for a long time.

• Several hens in the flock develop a swollen face or nasal discharge within a short time.
• A bird is breathing with its beak open or has rattling breathing.
• The eyes are so swollen that the bird cannot see and cannot find food and water.
• A bird stops eating and drinking.
• Along with a swollen head, there are sudden deaths, a bluish comb or bleeding on the legs.

These last signs may point to bird flu or Newcastle disease, which are notifiable diseases in Croatia. In that case, inform a vet or the veterinary inspectorate immediately and do not move the birds.

The vet examines the birds and takes a swab from the sinuses or nose for bacteriological or PCR testing. Similar signs can be caused by mycoplasmosis, fowl cholera, infectious laryngotracheitis, bird flu and vitamin A deficiency, so testing is important in order to choose the right treatment.

If a bird in the flock has died, put it in a sealed bag in a cool place and take it to the vet. Examining a dead bird often quickly reveals the cause of the disease and helps protect the rest of the flock.

Infectious coryza is treated with antibiotics prescribed by a vet, usually given in the water or feed to the whole flock. Treatment eases the disease and reduces losses, but it does not clear the bacterium from every bird, so the disease can come back.

• Give the medicine exactly as and for as long as the vet has prescribed.
• Observe the withdrawal period: the time during which eggs and meat from treated birds must not be eaten.
• Do not give birds antibiotics on your own initiative, because the wrong medicine or too short a course encourages bacterial resistance.

If the disease keeps coming back, the vet may advise restocking the flock with birds from a trusted breeder, along with thorough cleaning and disinfection of the henhouse.

• Separate sick birds from healthy ones in a dry, warm and well-ventilated space without draughts.
• Provide fresh water and easily accessible feed; clean the drinkers and change the water every day.
• Do not push food into the beak or pour in water.
• You can gently wipe away discharge around the eyes and nose with clean gauze soaked in lukewarm boiled water, using a fresh piece of gauze for each bird.
• Check on the sick birds last and wash your hands afterwards.

Infectious coryza is not dangerous to humans, but it is easily spread to other poultry via clothing, footwear and equipment.

• Only buy birds from trusted, coryza-free breeders.
• Keep new birds separate for several weeks before adding them to the flock.
• Do not mix birds of different ages and origins.
• Provide enough space, good ventilation and dry bedding.
• Clean and disinfect the drinkers, feeders and henhouse regularly.
• In areas where the disease is common, ask your vet about vaccination.

Infectious coryza rarely kills, but it wears the flock down and reduces laying, and birds that have recovered can go on spreading the bacterium. Quickly separating sick birds, treatment following the vet’s instructions and consistently quarantining new birds are the best protection.