Infectious Coryza in Chickens: Symptoms, Causes and Treatment

Avibacterium paragallinarum (formerly Haemophilus paragallinarum) is a gram-negative bacterium that requires V-factor (NAD) for growth and does not survive long in the environment. Despite this fragility, it spreads readily through infected birds.

• Carrier birds: Recovered chickens remain permanent subclinical carriers for life. Introducing a single carrier bird into a naive flock is the most common source of coryza outbreaks. This is why buying birds at auctions or from unknown sources carries high risk.
• Three serovars (A, B, C): Avibacterium paragallinarum exists in three serovars with limited cross-protection. Vaccination against one serovar may not prevent disease caused by another. This also explains why vaccinated flocks sometimes still get coryza.
• Contaminated water: The bacteria survive in drinking water for several hours. Shared water lines and drinkers are an efficient transmission route within a flock.
• Stress and co-infections: Mycoplasma gallisepticum, Newcastle disease, and IBV infections dramatically worsen coryza severity and duration.

The combination of rapid flock spread, characteristic facial swelling, and foul-smelling discharge is highly suggestive of coryza.

• Smell test: The discharge from coryza has a distinctively foul, sweet-sour odor unlike other respiratory diseases. This alone is a useful field diagnostic clue.
• Flock pattern: Coryza typically spreads to 80-100% of susceptible birds within 1-2 weeks. The facial swelling is more pronounced in birds housed in poor ventilation.
• Lab confirmation: Bacterial culture from sinus exudate on blood agar with a Staphylococcus nurse colony (for V-factor). PCR is more sensitive and faster. Serotyping (A, B, C) guides vaccine selection.
• Differentials: Mycoplasmosis (slower spread, no distinct odor), fowl cholera (more acute death), swollen head syndrome (different pathogen, turkey-associated), vitamin A deficiency (gape-like lesions without bacterial culture).

Infectious coryza responds well to antibiotics, but treatment suppresses rather than eliminates the organism. Recovered birds remain carriers regardless of treatment duration.

First-line therapy: Sulfadimethoxine (Albon) 0.05% in drinking water for 6 consecutive days. Alternatively, sulfamethazine at 0.2% in water for 2 days on, 3 days off, 2 days on. Trimethoprim-sulfamethoxazole combinations have shown good efficacy.

Alternative antibiotics: Erythromycin (200mg/gallon), tylosin, oxytetracycline, or amoxicillin are effective against susceptible strains. Increasing antibiotic resistance has been documented in some regions; lab sensitivity testing guides selection.

Duration of treatment: Treat for the full recommended course even if signs resolve early. Incomplete treatment increases the risk of resistant strains and carrier development.

Important caveat: Treatment clears clinical signs but does NOT eliminate the carrier state. Recovered birds must be considered permanent carriers and should not be mixed with uninfected flocks.

• Never introduce birds from unknown sources or auctions into a naive flock. If introducing new birds, quarantine for 30 days and observe for facial swelling or discharge before integration.
• Vaccinate in endemic areas using a bacterin that covers the serovars (A, B, C) circulating locally. Two doses 3-4 weeks apart are required for protection. Vaccination reduces severity but may not prevent infection.
• All-in, all-out flock management prevents carrier birds from serving as a reservoir for new arrivals.
• Cull or permanently isolate known carrier birds rather than reintroducing them to naive flocks after treatment.
• Disinfect water lines and drinkers regularly. Avibacterium paragallinarum survives in water for hours and spreads efficiently through shared drinkers.