Introduction
A usually acute, sometimes chronic, highly infectious disease of chickens, occasionally pheasants and guinea-fowl, characterised by catarrhal inflammation of the upper respiratory tract, especially nasal and sinus mucosae.
Infectious Coryza is caused by the bacterium Haemophilus paragallinarum and is seen in many countries especially in multi-age farms that are never depopulated. Morbidity is high but mortality low if uncomplicated although it may be up to 20%.
The route of infection is conjunctival or nasal with an incubation period of 1-3 days followed by rapid onset of disease over a 2-3 day period with the whole flock affected within 10 days, resulting in increased culling. Carriers are important with transmission via exudates and by direct contact. It is not egg transmitted.
The bacterium survives 2-3 days outside the bird but is easily killed by heat, drying and disinfectants. Intercurrent respiratory viral and bacterial infections are predisposing factors.
Signs
- Facial swelling.
- Purulent ocular and nasal discharge.
- Swollen wattles.
- Sneezing.
- Dyspnoea.
- Loss in condition.
- Drop in egg production of 10-40%.
- Inappetance.
Post-mortem lesions
- Catarrhal inflammation of nasal passages and sinuses.
- Conjunctivitis.
- Eye-lid adherence.
- Caseous material in conjunctiva/sinus.
- Tracheitis.
Diagnosis
A presumptive diagnosis may be made on signs, lesions, identification of the bacteria in a Gram-stained smear from sinus. Confirmation is by isolation and identification - requires X (Haematin) and V (NAD) factors, preferably in raised CO2 such as a candle jar. Serology: HI, DID, agglutination and IF have all been used but are not routine.
Differentiate from Mycoplasmosis, respiratory viruses, chronic or localised pasteurellosis and vitamin A deficiency.
Treatment
Streptomycin, Dihydrostreptomycin, sulphonamides, tylosin, erythromycin. Flouroquinolones are bactericidal and might prevent carriers.
Prevention
Stock coryza-free birds on an all-in/all-out production policy. Bacterin at intervals if history justifies or if multi-age; at least two doses are required. Commercial bacterins may not fully protect against all field strains but reduce the severity of reactions. Live attenutated strains have been used but are more risky. Controlled exposure has also been practised.
Vaccines are used in areas of high incidence. Birds recovered from challenge of one sero-type are resistant to others, while bacterins only protect against homologous strains.