Infectious Coryza
Etiology
Infectious coryza (IC) is a respiratory disease primarily affecting chickens and occasionally pheasants and guinea-fowl. The disease is caused by Avibacterium paragallinarum, a gram-negative nonmotile bacterium.
Host Range
IC primarily affects chickens. Turkeys, ducks, and other wild avian species appear to be refractory to the infection. The disease has no public health significance for humans.
Epidemiology
IC is primarily spread through chronically infected carrier birds. Airborne transmission and contaminated drinking water may help spread the infection to susceptible birds. Chickens of all ages are susceptible; however the disease is usually less severe in immature birds. In the absence of concurrent infection, infected birds typically recover in 2-3 weeks. Hens in lay typically have a shorter incubation period and the course of the disease tends to be longer. Birds that recover frequently become chronic carriers.
IC is distributed worldwide. Both commercial chickens as well as village chickens appear to be equally at risk. The disease can cause significant economic losses in intensive poultry operations, especially in multi-age farms. In developing countries, stress factors and the presence of concurrent infections frequently exacerbate losses.
Clinical Signs
The incubation period for IC is approximately 1-3 days. The severity of infection varies depending on the age, breed, environmental stress, and presence of concurrent infections.
In the mild form, typically seen in young chickens, birds may become depressed and have nasal discharge and mild swelling of the face.
In the severe form, typically seen in young adults, there is an acute infection of the upper respiratory tract. Signs may include serous to mucoid nasal discharge, swelling of the infraorbital sinuses, facial edema including swollen eyelids that do not open, swollen wattles and intermandibular space, and conjunctivitis. If the lower respiratory tract becomes involved, rales may be observed. Signs usually persist for only a few weeks, however, if secondary infection occurs, the swelling can persist for months. Feed consumption, egg production, and growth are often severely reduced.
Post-mortem Lesions
On post-mortem examination, gross lesions may be found on the mucous membranes of the nasal passages, sinuses, and ocular conjunctiva. Findings may include inflammation and catarrhal lesions. Subcutaneous edema may be found in the face, wattles, and intermandibular region. Rarely, pneumonia and airsacculitis may be present.
Differential Diagnosis
Swelling of the face and wattles must be differentiated from chronic fowl cholera, Newcastle disease, infectious bronchitis, avian influenza, avian metapneumovirus (swollen head syndrome), mycoplasmosis, and infectious laryngotracheitis. A nonpathogenic species, Avibacterium avium, may be cultured from the sinus of chickens, either alone or in combination with A. paragallinarum. A. paragallinarum is catalase negative, while nonpathogenic species are catalase positive.
Diagnosis
A smear of sinus exudate can be made and Gram stained, which will reveal Gram-negative, bipolar-staining rods with a tendency toward filament formation. The sinus exudate should be cultured on a blood agar plate, previously streaked with Staphylococcus aureus. This will serve as a feeder colony by providing V-factor. The plate should be incubated in a candle jar or CO2 incubator. Tiny dewdrop-like colonies of A. paragallinarumc will develop adjacent to the feeder colony. The organism can be further identified by biochemical tests or polymerase chain reaction (PCR). Serologic tests include agar gel precipitation and hemagglutination-inhibition.
Prevention and Control
Management practices that include all in, all out of flocks, help to prevent and control the disease. Antimicrobial therapy is very effective but it should be used according to specific residue regulations in birds producing eggs for human consumption.
Commercially available IC vaccines are inactivated whole cell bacterins. They may contain one or several isolates representing various serogroups. In severe outbreaks, autogenous vaccines are commonly used. Broilers are not commonly vaccinated against IC. In many countries, replacement layers and breeders receive two vaccinations subcutaneously or intramuscularly, at least four weeks apart, before twenty weeks of age.
Selected References
- Blackall, P.J. 2008. Infectious Coryza. In A Laboratory Manual for the Isolation and Identification of Avian Pathogens, 5th edition. L. Dufour-Zavala Louise et al. (ed.) OmniPress, Inc., Madison, Wisconsin.
- Blackall, P.J. and E.V. Soriano. 2008. In Diseases of Poultry, 12th ed. Y.M. Saif. et al. (ed.). Blackwell Publishing, Ames, Iowa.
- Blackall, P.J. 1999. Infectious Coryza: overview of the disease and new diagnostic options. Clin Microbiol Rev Oct;12(4):627-32. Review.
- Charlton, B. R. (ed). 2006. Avian Disease Manual, 6th ed. American Association of Avian Pathologists (AAAP), 953 College Station Road, Athens, Georgia 30602-4875.
- Glisson, J.R. 1998. Bacterial respiratory disease of poultry. Poult Sci Aug;77(8):1139-42. Review.
- World Organization for Animal Health (OIE) website. 2008. www.oie.int
Thank you to the following individuals for reviewing these materials:
Richard Chin
Jose Bruzual
Morella DeRosa
