Infectious Bronchitis in Chickens: Symptoms, Causes and Treatment

Infectious bronchitis virus (IBV) is an avian gammacoronavirus with dozens of serotypes, many of which do not cross-protect against each other. This makes complete vaccine protection difficult to achieve.

• Airborne transmission: IBV is shed in respiratory secretions and feces. In susceptible flocks, airborne spread can infect all birds within 24-48 hours. Virus can travel on wind between farms.
• Fomite and equipment spread: Contaminated clothing, equipment, vehicles, and feed bags carry virus between flocks. IBV survives on surfaces for hours at room temperature.
• Multiple serotypes: Massachusetts, Connecticut, Delaware, Arkansas, California and numerous other serotypes circulate regionally. Vaccination against one serotype does not protect against others, explaining why vaccinated flocks sometimes still get IB.
• Stress triggers: Chilling, ammonia buildup, and concurrent infection with Mycoplasma or E. coli dramatically worsen clinical signs and increase mortality.

Presumptive diagnosis is based on the rapid spread of respiratory signs combined with acute egg production drops and shell quality changes in layers. No other disease causes this exact pattern so quickly.

• Flock pattern: If 80-100% of birds show respiratory signs within 48 hours, IBV is the most likely cause. Newcastle disease causes similar spread but more severe neurological signs.
• Egg quality change: Watery thin albumin (egg white) is nearly pathognomonic for IB in laying flocks. Shells may be rough, misshapen, or thin.
• Lab confirmation: Reverse transcription PCR (RT-PCR) on tracheal swabs or fresh tissues identifies the virus. Serology (ELISA, HI test) confirms exposure but doesn't differentiate strains.
• Nephropathogenic strains: Some IBV strains (Holte, Gray) attack kidneys causing pale, swollen kidneys with urate deposits visible at necropsy. These strains cause higher mortality.

There is no antiviral treatment for infectious bronchitis. Management focuses on supportive care and preventing secondary bacterial infections.

Supportive care: Maintain optimal brooder temperature (95F at day 1, reducing 5F per week). Reduce stocking density to improve air quality. Provide vitamins and electrolytes in drinking water. Ensure ventilation removes ammonia without chilling birds.

Secondary infection control: Bacterial superinfection (E. coli air sacculitis, Mycoplasma) significantly increases mortality. Prophylactic broad-spectrum antibiotics (oxytetracycline, tylosin, or enrofloxacin under veterinary guidance) are commonly used to control secondary pathogens during the acute phase.

Egg production recovery: In uncomplicated IB, most flocks recover egg production within 4-6 weeks. Severe or nephropathogenic strains may cause permanent reduction in production capacity in some hens due to oviduct scarring in early infections.

• Vaccinate all chicks at hatch with a spray or eye-drop Massachusetts-type live vaccine, followed by a booster at 2-3 weeks. In high-risk areas, add a killed oil-emulsion vaccine at 16 weeks in layers.
• Use regionally appropriate vaccine strains. Contact your state veterinarian or poultry diagnostic lab to identify the IBV serotypes circulating in your area before choosing a vaccine.
• Practice all-in, all-out flock management. Avoid mixing birds of different ages on the same premises, as older birds can be immune carriers that infect susceptible young birds.
• Strict biosecurity: foot baths at entry, dedicated clothing and equipment for each flock house, vehicle disinfection.
• Minimize co-infection risk: keep Mycoplasma and Newcastle disease vaccinations current, as these dramatically worsen IB outcomes.