Infectious coryza is an acute respiratory disease of chickens characterized by nasal discharge, sneezing, and swelling of the face under the eyes. It is distributed worldwide and is quite important in tropical and temperate climates. Although it occurs in pheasants and Japanese quail, the disease is primarily one of chickens, mainly of pullets and layers and occasionally of broilers. In the USA, it is most prevalent in commercial flocks in California and the southeast. The disease has no public health significance.
Etiology: The causative bacterium, Haemophilus paragallinarum(gallinarum) , is a gram-negative, pleomorphic, nonmotile, catalase-negative, microaerophilic rod that requires nicotinamide adenine dinucleotide (V-factor) for 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. Recently, V-factor-independent H paragallinarum have been recovered in South Africa. Haemophilus paragallinarum is grouped into three serovars (A, B, and C) that are correlated with immunotype specificity.
Epidemiology and Transmission: 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 duration of the disease usually 2-3 wk. Under field conditions, the disease may run up to several weeks in the presence of concurrent diseases, eg, mycoplasmosis.
Once a flock has been infected, it is 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 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 enzyme analysis and monoclonal antibodies that identify strains have been used to trace outbreaks of infectious coryza.
Clinical Findings: In the mildest form of the disease (usually seen in young Leghorns or broilers), the only signs may be depression, a serous nasal discharge, and occasionally slight facial swelling. In the more severe form (usually seen in young adult Leghorns or heavy breeders), 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, the swelling can persist for months. There may be varying degrees of rales depending on the extent of infection. 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.
Lesions: 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. 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.
Diagnosis: Isolation of a catalase-negative, nurse-colony-dependent organism from chickens in a flock with a history of a rapidly spreading coryza is diagnostic. Production of typical signs after inoculation with nasal exudate from infected into susceptible chickens is also reliable diagnostically. Antibodies may be detected by agglutination, agar-gel precipitation, or hemagglutination-inhibition ~2-3 wk after infection. Swelling of the face and wattles must be differentiated from fowl cholera (Fowl Cholera). Other diseases that must be considered are mycoplasmosis, laryngotracheitis, Newcastle disease, infectious bronchitis, avian influenza, swollen head syndrome, and vitamin A deficiency.
While currently found only in South Africa, the presence of V-factor-independent H paragallinarum must also be considered. Further biochemical tests may be necessary to clearly identify such isolates.
Control and Treatment: 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 the disease. 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. The immunization should be given ~4 wk before infectious coryza usually breaks out on the individual farm. Antibodies detected by the hemagglutination-inhibition test after bacterin administration 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) have been found to be active against infectious coryza. Various sulfonamides and sulfonamide-trimethoprim and other combinations have been successful but must not be used in layers. 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 in which started pullets are to be reared or housed on infected premises.