Infectious coryza is an acute respiratory disease of chickens characterized by nasal discharge, sneezing, and facial swelling below the eyes. It is a disease that occurs worldwide and is limited to chickens. Reports of disease in quail and pheasants probably describe a similar disease caused by a different agent. It is caused by the gram-negative bacterium Avibacterium paragallinarum.
Epidemiology and transmission
Chronically infected birds as well as healthy carriers are the main reservoirs of the infection. Chickens of all ages are susceptible, but their susceptibility increases with age. The incubation period is 1 to 3 days and the duration of the disease is 2 to 3 weeks, although the duration of the disease may be longer depending on farm conditions such as the presence of other diseases such as mycoplasmosis. Transmission occurs by direct contact, airborne droplets, and contaminated drinking water, and infected flocks pose a constant threat to uninfected flocks.
Clinical findings
In the mildest form of the disease, only signs of depression, serous nasal discharge, and in some cases, slight facial swelling may be noted. In the more severe form of the disease, there is severe swelling of one or both sinuses with edema of the surrounding tissue, causing one or both eyes to close. Facial swelling usually subsides within 10-14 days; however, if secondary infection occurs, this swelling may persist for months. Egg production may be delayed in young pullets (layers) and severely reduced in production hens. Birds may have diarrhea and feed and water consumption is usually reduced in the acute stage of the disease.
Lesions
In acute cases, lesions may be confined to the infraorbital sinuses, with copious, semi-watery, grayish-white discharge. As the disease progresses or other pathogens become involved, the sinus discharge may become thick and yellowish in consistency. Lesions may include conjunctivitis, trachea, bronchi, and alveolitis, especially if other pathogens are involved. The histopathologic response of the respiratory organs includes mucosal and glandular epithelial breakdown and hyperplasia, and edema with infiltration by heterophils, macrophages, and mast cells.
Diagnosis
Isolation of a gram-negative organism with a negative catalase test from a flock of chickens with a history of rapidly developing coryza is diagnostic. Catalase testing is essential for the diagnosis of this disease, as nonpathogenic hemophilic organisms, with catalase-positive test, are present in healthy chickens as well as in diseased chickens. PCR testing is better than microbial culture and has been widely used for the diagnosis of this disease even in developing countries.
Real-time PCR testing is also used for the diagnosis of this disease. The appearance of typical signs of the disease after inoculation of nasal secretions of infected chickens with susceptible chickens is diagnostically reliable, currently there is no suitable serological test for diagnosis, however, the hemagglutination inhibition test is the best available test.
Differential diagnosis of coryza should be made from other diseases with similar symptoms such as facial edema in fowl cholera or other diseases including mycoplasmosis, infectious laryngotracheitis, Newcastle disease, infectious bronchitis, avian influenza, head-and-neck syndrome and also vitamin A deficiency.
Treatment and Prevention
Prevention is considered the only effective control method. An all-in/all-out system, combined with proper management and isolation, is the best way to prevent coryza infection. Vaccination should be carried out 4 weeks before the onset of coryza infection on the farm. Inactivated bivalent (serotypes A-1, C-1) or trivalent (A-1, B-1, C-2) vaccines can help prevent the disease, depending on the prevalence of serotypes in geographical areas at 10-12 weeks and 16-18 weeks and one year of age. However, it has been described that vaccines do not provide sufficient protection, such as the prevalence of serotype B strains, which are highly pathogenic, although the spread of the organism can be controlled to some extent by removing all sick birds with clinical signs.
Erythromycin and oxytetracycline are usually effective in treating coryza, and newer antibiotics such as fluoroquinolones and macrolides may be active against infectious coryza. Although treatment may improve, the disease may recur if the medication is discontinued.
References:
Overview of Infectious Coryza in Chickens (https://www.msdvetmanual.com/poultry/infectious-coryza/infectious-coryza?autoredirectid=24942&autoredirectid=14422)
Infectious_Coryza (https://www.researchgate.net/publication/304321575_Infectious_Coryza)
