Introduction
Infectious coryza is an acute respiratory disease in poultry, primarily affecting chickens. It is caused by Avibacterium paragallinarum, a Gram-negative, catalase-negative bacterium. The disease is characterized by facial swelling, nasal discharge, and respiratory distress, leading to significant economic losses in commercial poultry due to decreased egg production and poor growth performance.
Causative Agent
The etiological agent, Avibacterium paragallinarum, belongs to the Pasteurellaceae family. It has three serotypes—A, B, and C—based on antigenic variations. The bacterium is facultatively anaerobic and requires specific growth factors (such as V-factor) for laboratory culture.
Epidemiology
Host Range: Primarily affects chickens of all ages, but older birds show more severe symptoms.
Transmission: Spread occurs through direct contact, aerosol droplets, contaminated feed, and water. Carrier birds serve as a major reservoir.
Risk Factors: Poor biosecurity, overcrowding, concurrent infections (such as Mycoplasma spp.), and stress predispose birds to infection.
Pathogenesis
The bacteria colonize the upper respiratory tract, damaging ciliated epithelium and leading to inflammation. This results in:
- Conjunctivitis with eyelid swelling
- Facial edema due to sinus inflammation
- Mucopurulent nasal discharge
- Airway narrowing, causing breathing difficulties
Clinical Signs
The disease can present in two forms:
Mild Form:
- Listlessness
- Serous nasal discharge
- Slight facial swelling
Severe Form:
- Pronounced swelling of infraorbital sinuses
- Edema extending to surrounding tissues
- Closure of eyes due to excessive swelling
- Difficulty in breathing due to airway obstruction
- Drop in egg production (up to 10-40% in layers)
Differential Diagnoses
Infectious coryza must be distinguished from:
- Mycoplasmosis (Mycoplasma gallisepticum)
- Infectious laryngotracheitis (ILT)
- Fowl cholera (Pasteurella multocida)
- Avian influenza
- Newcastle disease (ND)
- Vitamin A deficiency
- Swollen Head Syndrome (avian metapneumovirus)
Diagnosis
- Clinical Signs: Facial swelling, nasal discharge, and respiratory distress.
- Laboratory Tests:
- Bacterial Culture: Requires specific growth conditions (NAD-dependent media).
- PCR Assay: Detects Avibacterium paragallinarum DNA from swabs.
- Serotyping: Differentiates between serotypes A, B, and C.
Treatment and Control
Antibiotic Therapy
- Erythromycin: Effective against Gram-negative respiratory pathogens.
- Oxytetracycline: Broad-spectrum antibiotic used in drinking water.
- Sulfonamides: Sulfa drugs (e.g., sulfadimethoxine) are commonly used for respiratory infections.
Prevention Strategies
1. Biosecurity Measures:
Isolate infected birds to prevent disease spread.
Disinfect water sources and equipment regularly.
Limit farm visitors to reduce contamination risks.
2. Vaccination:
Administer vaccines containing local serovars between 10-20 weeks of age.
Multiple-age flock management increases disease risk.
3. Environmental Management:
Provide proper ventilation to reduce airborne spread.
Minimize stress factors like overcrowding and sudden temperature changes.
Conclusion
Infectious coryza remains a significant challenge in poultry farming, leading to economic losses due to reduced productivity. Early diagnosis, antibiotic therapy, and strict biosecurity practices are essential to control outbreaks. Vaccination using region-specific serovars plays a crucial role in long-term prevention.
FAQ’s
- What causes infectious coryza?
- Caused by Avibacterium paragallinarum, a bacterium.
- What are the key symptoms?
- Facial swelling, nasal discharge, sneezing, and reduced egg production.
- How is it transmitted?
- Direct contact, aerosols, contaminated equipment, or carrier birds.
- Can it affect humans?
- No, it is not zoonotic.
- How is it treated?
- Antibiotics (e.g., erythromycin), but carriers may remain.
