Air Sacculitis in Chickens: Symptoms, Causes and Treatment

Air sacculitis is the result of a two-hit process: a primary pathogen damages the air sac epithelium, then secondary opportunistic bacteria colonize the compromised tissue.

• Primary pathogens: Mycoplasma gallisepticum (MG) is the most common primary agent, damaging the ciliated epithelium of the air sac lining and impairing mucociliary clearance. Infectious Bronchitis Virus (IBV) and Newcastle Disease Virus can also initiate the same process. Immunosuppression from IBD or CIA removes the immune defense that would normally prevent colonization.
• Secondary bacterial pathogens: E. coli (most common) colonizes the damaged air sac lining and produces the cheesy exudate that characterizes advanced air sacculitis. Pasteurella, Hemophilus, and Salmonella can also be involved as secondary invaders.
• The "complicated chronic respiratory disease" syndrome: The combination of MG + E. coli air sacculitis is the most economically important respiratory syndrome in commercial poultry worldwide and is now considered a standard pathological unit.
• Environmental stress amplification: High ammonia levels, poor ventilation, dust, and temperature extremes dramatically worsen both the primary Mycoplasma infection and the secondary E. coli colonization of damaged air sacs.

Rattling breath sounds on auscultation or simply at rest are the hallmark sign of air sacculitis. Necropsy confirms the diagnosis.

• Physical exam: Hold the bird quietly and listen for rattling, gurgling, or clicking sounds with each breath. In severe cases, breathing sounds are audible without any instrument.
• Auscultation: A stethoscope placed over the syrinx (junction of trachea and bronchi, at the sternum base) reveals rattling or crackling sounds in affected birds.
• Necropsy: Air sacs are normally transparent and paper-thin. In air sacculitis, they are opaque, thickened, and contain yellow to white cheesy exudate. The extent (anterior vs. all sacs) indicates severity and chronicity.
• Culture and sensitivity: E. coli from air sac exudate should be tested for antibiotic sensitivity. E. coli resistance patterns vary by region and previous antibiotic exposure history.

Treatment must address both the primary pathogen (Mycoplasma or virus) and the secondary bacterial infection (usually E. coli).

For Mycoplasma-associated air sacculitis: Tylosin 50-100 mg/gallon for 5-7 days, or tiamulin 250 mg/gallon for 3-5 days. These target MG as the primary pathogen.

For secondary E. coli: Enrofloxacin (under veterinary prescription) or trimethoprim-sulfamethoxazole targets gram-negative secondary bacteria. Sensitivity testing guides drug selection as fluoroquinolone resistance is increasing.

Combination therapy: In severe outbreaks, tylosin (or tiamulin) plus a fluoroquinolone or tetracycline simultaneously addresses both the primary Mycoplasma and the secondary E. coli.

Environmental management: Reducing ammonia to below 25 ppm, increasing ventilation, and reducing stocking density are the most impactful supportive measures. High ammonia is both a cause and a perpetuator of air sacculitis.

• Vaccinate against Mycoplasma gallisepticum using live F-strain or ts-11 vaccine at the appropriate age. MG vaccination significantly reduces air sacculitis incidence by preventing the primary predisposing infection.
• Vaccinate against Newcastle disease and infectious bronchitis on schedule. These viruses initiate the same air sac damage as MG and set up the same secondary E. coli colonization.
• Maintain litter quality and ventilation. Ammonia above 25 ppm directly damages the respiratory epithelium. Check ammonia at bird level, not the doorway, where levels are always lower.
• Avoid overcrowding. Stocking density above recommendations concentrates respiratory pathogens and reduces ventilation per bird.