Infectious coryza is an acute respiratory disease of chickens characterized by decreased activity, nasal discharge, sneezing, and facial swelling that occurs worldwide. The disease apparently affects only chickens; reports in quail and pheasants likely describe a similar disease caused by a different bacterium.
In countries such as the US, the disease is seen primarily in pullets and laying hens and occasionally in broilers. It is most prevalent in commercial flocks in California and the southeastern states, although flocks in the northeast have experienced notable outbreaks. In lower- and middle-income countries, the disease often is seen in very young chicks (eg, 3 weeks old). Inadequate biosecurity practices Biosecurity of Animals The tenets of biosecurity have been long recognized by veterinarians. However, throughout the past decades, interest in biosecurity as a scientific discipline has surged because of 1) disease... read more and environmental factors may contribute. Infectious coryza is not a zoonotic disease, and thus lacks public health importance.
Etiology of Infectious Coryza in Chickens
The causative bacterium of infectious coryza is Avibacterium paragallinarum, a gram-negative, pleomorphic, nonmotile, catalase-negative, microaerophilic rod that requires nicotinamide adenine dinucleotide (V-factor) for culture. When cultured on blood agar with a staphylococcal nurse colony that excretes the V-factor, the satellite colonies appear as dewdrop shapes, growing adjacent to the nurse colony. V-factor–independent A paragallinarum have been reported in South Africa and Mexico. The most commonly used serotyping scheme is the Page scheme, which groups A paragallinarum isolates into three serovars (A, B, and C) that correlate with immunotype specificity.
Epidemiology and Transmission of Infectious Coryza in Chickens
Chronically ill or healthy carrier birds are the reservoir of infection for A paragallinarum. Chickens of all ages are susceptible; however, susceptibility increases with age. The incubation period is 1–3 days with a typical disease duration of 2–3 weeks. Duration of illness may be longer in the presence of concurrent diseases such as mycoplasmosis Mycoplasmosis in Poultry Mycoplasmas are bacteria that lack a cell wall, are small in size, and have the smallest genome among all independently replicating forms of life .Because of their small genome and the lack... read more .
Infected flocks are a constant threat to uninfected flocks. Transmission is by direct contact, airborne droplets, and contamination of drinking water. Transmission does not occur via eggs. “All-in/all-out” management has essentially eradicated infectious coryza from many commercial poultry operations in the US. Such programs move all animals of the same age at the same time. This flow allows birds in the same enclosures to be exposed to any pathogen(s) at the same time. Facilities are disinfected before new next group of new animals are added. Commercial farms without such flow and multiple-age flocks may continue to see outbreaks of the disease. Molecular techniques such as restriction endonuclease analysis and ribotyping have been used to trace outbreaks of infectious coryza.
Clinical Findings of Infectious Coryza in Chickens
In the mildest form of infectious coryza, the only signs may be listlessness, a serous nasal discharge and occasionally slight facial swelling. With increased severity extreme swelling of one or both infraorbital sinuses with edema of the surrounding tissues may prevent the eyes from fully opening. In adult birds, especially males, the edema may extend to the intermandibular space and wattles. The swelling usually abates in 10–14 days; however, if secondary infection occurs it can persist for months. There may be varying degrees of rales depending on the extent of infection. In Argentina, a form of the disease involving bacteremia has been reported, likely due to concurrent infections. Egg production may be delayed in young pullets and severely reduced in producing hens. Affected birds may have diarrhea and feed and water consumption usually is decreased during acute stages of the disease.
In acute cases, only the infraorbital sinuses may be involved and contain copious, grayish, semifluid exudate evident on gross inspection and during histopathologic examination. With chronicity this exudate may become consolidated. Histopathologic features include edema, hyperplasia and erosion of respiratory mucosal and glandular epithelia and edema with infiltration of heterophils, macrophages, and mast cells. Other lesions may include conjunctivitis, tracheitis, bronchitis, and airsacculitis, particularly if other pathogens are involved.
Diagnosis of Infectious Coryza in Chickens
Bacterial culture or PCR assay
Isolation of a gram-negative, satellitic, catalase-negative organism from chickens in a flock with a history of a rapidly spreading disease is diagnostic for infectious coryza. A catalase specific test is essential as nonpathogenic hemophilic organisms, which are catalase-positive, are present in both healthy and diseased chickens. Polymerase chain reaction testing of live flocks assay has been reported to provide more accurate results versus to bacterial culture, including in countries with lesser resources. A real-time version of the PCR assay is available. Production of typical signs after inoculation with nasal exudate from infected into susceptible chickens is also reliable diagnostically. No suitable serologic test exists; a hemagglutination-inhibition test exists but is not preferable to other methods.
Important differential diagnoses are:
swollen head syndrome (ornithobacteriosis)
Although currently found only in South Africa and Mexico, the presence of a V-factor–independent A paragallinarum must also be considered. The A paragallinarum PCR assay is an ideal diagnostic tool in this situation.
Control and Treatment of Infectious Coryza in Chickens
Sound management practices and vaccination can help prevent infection
Prompt antimicrobial treatment with supportive care of infected birds to aid recovery
Prevention is the only sound method of control for infectious coryza. All-in/all-out flow of animals as part of sound farm management and biosecurity practices are important disease prevention measures. Replacement chickens should be raised on the same farm or obtained from clean flocks. If replacement pullets are to be placed on a farm that has a history of infectious coryza, bacterins/vaccines are available to help prevent and control the disease. USDA-licensed commercially produced bacterins are available, and bacterins also are produced within states for intrastate use. Bacterins/vaccines also are produced in many other countries. Because serovars A, B, and C are not cross-protective, it is essential that bacterins contain the serovars present in the target population.
Vaccination on individual farms should be completed ~4 weeks before infectious coryza outbreaks typically occur. Antibodies detected by the hemagglutination-inhibition test after bacterin administration do not necessarily correlate with protective immunity. Controlled exposure to live organisms also has been used to produce protective immunity in layers in endemic areas.
Because early treatment is important, immediate administration of medication via drinking water is recommended until medicated feed is available. Erythromycin and oxytetracycline are usually effective. Additionally, several newer-generation antimicrobials (eg, fluoroquinolones, macrolides) are active against infectious coryza. Various sulfonamides, including trimethoprim-sulfamethoxazole, and other drug combinations have been successful for treatment. Antimicrobial use in chickens is subject to national regulations that vary from country to country, and use and efficacy must be reviewed in light of relevant laws. In more severe outbreaks, although treatment may result in improvement, the disease may recur when medication is discontinued.
Preventive medication may be combined with a vaccination program if started pullets are to be reared or housed on infected premises.
Infectious coryza is an upper respiratory disease caused by Avibacterium paragallinarum affecting chickens.
Diagnosis is by means of bacteriologic culture or PCR assay.
The main preventive strategies are all in/all out management and sound biosecurity measures combined with appropriate vaccination.