Infectious Coryza

    Infectious coryza is an acute respiratory disease of chickens characterized by nasal discharge, sneezing, and swelling of the face under the eyes. It is seen worldwide,but, only in chickens.

In developed countries such as the USA, the disease is seen primarily in pullets and layers and occasionally in broilers. In developing countries, the disease often is seen in very young chicks, even as young as 3 wk of age. Poor biosecurity, poor environment, and the stress of other diseases are probably the main reasons why infectious coryza is more of a problem in developing countries. 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 in vitro growth. V-factor-independent H paragallinarum have been recovered in South Africa and Mexico. The most commonly used serotyping scheme is the Page scheme, which groups H paragallinarum isolates into 3 serovars (A, B, and C) that correlate 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 the disease duration is usually 2-3 wk. Under field conditions, the duration may be longer in the presence of concurrent diseases, eg, mycoplasmosis.

Transmission is by direct contact, airborne droplets, and contamination of drinking water. “All-in/all-out” management can essentially eradicated infectious coryza from  commercial poultry farms. 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.

Clinical Findings:

Infectious coryza, swollen sinuses, hen
 
 
In the mild form of the disease, the only signs may be depression, a serous nasal discharge, and occasional slight facial swelling. In the 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 subsides in 10-14 days; in case of secondary infection swelling can persist for months, varying degrees of rales is there, depending on the extent of infection.Egg production may be delayed in young pullets and severely reduced in producing hens. Birds may have diarrhea. Feed and water consumption is decreased during acute stages of the disease.

Lesions:

In acute cases, lesions may be limited to the infra-orbital sinuses with a copious, tenacious, grayish, semi-fluid 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 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, as nonpathogenic Haemophilus 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.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 the available tests. Swelling of the face and wattles must be differentiated from that seen in 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 H paragallinarummust also be considered. The H paragallinarum PCR is an ideal diagnostic tool in this situation.

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. 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 breaks out . 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.

Erythromycin and oxytetracycline ,several new-generation antibiotics (eg, fluoroquinolones, macrolides) are active against infectious coryza. Various sulfonamides, sulfonamide-trimethoprim, and other combinations are successful but not favored in layers. In more severe outbreaks, although treatment may result in improvement, but care should be taken 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 a premises with previous history.
Reference :- Merck Veterinary Manual
 
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