Overview of Infectious Coryza in Chickens
Infectious coryza is an acute respiratory disease of chickens characterized by nasal discharge, sneezing, and swelling of the face under the eyes. It is found worldwide. The disease is seen only in chickens; reports of the disease in quail and pheasants probably describe a similar disease that is caused by a different etiologic agent.
In developed countries such as the USA, the disease is seen primarily in pullets and layers and occasionally in broilers. In the USA, it is most prevalent in commercial flocks in California and the southeast, although the northeastern USA has experienced significant outbreaks. In developing countries, the disease often is seen in very young chicks, even as young as 3 wk old. Poor biosecurity, poor environment, and the stress of other diseases are likely reasons why infectious coryza is more of a problem there. The disease has no public health significance.
The causative bacterium is Avibacterium paragallinarum, a gram-negative, pleomorphic, nonmotile, catalase-negative, microaerophilic rod that requires nicotinamide adenine dinucleotide (V-factor) for in vitro growth. When grown on blood agar with a staphylococcal nurse colony that excretes the V-factor, the satellite colonies appear as dewdrops, growing adjacent to the nurse colony. V-factor–independent Av paragallinarum have been recovered in South Africa and Mexico. The most commonly used serotyping scheme is the Page scheme, which groups Av paragallinarum isolates into three serovars (A, B, and C) that correlate with immunotype specificity.
Chronically ill or healthy carrier birds are the reservoir of infection. Chickens of all ages are susceptible, but susceptibility increases with age. The incubation period is 1–3 days, and the disease duration is usually 2–3 wk. Under field conditions, the duration may be longer in the presence of concurrent diseases, eg, mycoplasmosis.
Infected flocks are a constant threat to uninfected flocks. Transmission is by direct contact, airborne droplets, and contamination of drinking water. “All-in/all-out” management has essentially eradicated infectious coryza from many commercial poultry establishments in the USA. Commercial farms that have multiple-age flocks tend to perpetuate the disease. Egg transmission does not occur. Molecular techniques such as restriction endonuclease analysis and ribotyping have been used to trace outbreaks of infectious coryza.
In the mildest form of the disease, the only signs may be depression, a serous nasal discharge, and occasionally slight facial swelling. In the more severe form, there is severe swelling of one or both infraorbital sinuses with edema of the surrounding tissue, which may close one or both eyes. 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, swelling can persist for months. There may be varying degrees of rales depending on the extent of infection. In Argentina, a septicemic form of the disease has been reported, probably due to concurrent infections. Egg production may be delayed in young pullets and severely reduced in producing hens. Birds may have diarrhea, and feed and water consumption usually is decreased during acute stages of the disease.
In acute cases, lesions may be limited to the infraorbital sinuses. There is a copious, tenacious, grayish, semifluid exudate. As the disease becomes chronic or other pathogens become involved, the sinus exudate may become consolidated and turn yellowish. Other lesions may include conjunctivitis, tracheitis, bronchitis, and airsacculitis, particularly if other pathogens are involved. The histopathologic response of respiratory organs consists of disintegration and hyperplasia of mucosal and glandular epithelia and edema with infiltration of heterophils, macrophages, and mast cells.
Isolation of a gram-negative, satellitic, catalase-negative organism from chickens in a flock with a history of a rapidly spreading coryza is diagnostic. The catalase test is essential, because nonpathogenic hemophilic organisms, which are catalase-positive, are present in both healthy and diseased chickens. A PCR test that can be used on the live chicken and that has proved superior to culture, even in developing countries, has been developed. A real-time version of the PCR is also 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 is the best of those available. Swelling of the face and wattles must be differentiated from that seen in fowl cholera (see Fowl Cholera). Other diseases that must be considered are mycoplasmosis, laryngotracheitis, Newcastle disease, infectious bronchitis, avian influenza, swollen head syndrome (ornithobacterosis), and vitamin A deficiency.
While currently found only in South Africa and Mexico, the presence of a V-factor–independent Av paragallinarum must also be considered. The Av paragallinarum PCR is an ideal diagnostic tool in this situation.
Prevention is the only sound method of control. “All-in/all-out” farm programs with sound management and isolation methods are the best way to avoid infectious coryza. Replacements 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 are available to help prevent and control the disease. USDA-licensed bacterins are available, and bacterins also are produced within states for intrastate use. Bacterins 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 should be completed ~4 wk before infectious coryza usually breaks out on the individual farm. 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 immunize layers in endemic areas.
Because early treatment is important, water medication is recommended immediately until medicated feed is available. Erythromycin and oxytetracycline are usually beneficial. Several new-generation antibiotics (eg, fluoroquinolones, macrolides) are active against infectious coryza. Various sulfonamides, sulfonamide-trimethoprim, and other combinations have been successful. Antibiotic use in chickens is subject to national regulations that vary from country to country, and use and efficacy of the various antibiotics must be reviewed in the light of the relevant national regulations. 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.