Infectious bronchitis (IB) is a widespread rapidly spreading, highly contagious respiratory infection caused by a coronavirus. It primarily affects the chicken's upper respiratory tract, although sometimes it spreads to the renal and reproductive systems. There are several types of vaccines available, however the emergence of multiple strands of the virus have made control difficult.
Outbreaks of infectious bronchitis frequently occur worldwide, even in vaccinated flocks. The disease spreads rapidly among chickens in a flock, resulting in all birds eventually becoming infected, in a short period of time. Susceptible birds placed with infected chickens usually develop clinical signs of illness within 24–48 hours. Chickens of all ages and breed types are susceptible to IBV infection, but the extent and severity of the disease is pronounced in young chicks, compared to adults. Similarly, resistance to infection was suggested to increase with increasing age
What are the Signs of Infectious Bronchitis?
Infectious bronchitis predominately infects the upper respiratory system, resulting in sneezing, gasping, coughing, tracheal rales, nasal discharge, sometimes wet eyes, and occasionally swollen sinuses. Chicks may appear depressed and be seen huddled under a heat source. Laying chickens affected will show a drop in egg production for about two weeks. The eggs often have irregular and roughened eggshells with watery albumin. Watery albumen with yolk separated from thick album (eggs). Infectious bronchitis resembles several other acute respiratory diseases such as Newcastle disease, infectious laryngotrancheitis, low pathogenicity avian influenza, and infectious coryza.
What are the potential complications of infectious bronchitis?
- Secondary bacterial infections: IBV damages the chicken's respiratory epithelium, often predisposing young chicks to secondary infections with pathogenic bacteria, such as Escherichia coli and Mycoplasma spp. Two of the most common secondary manifestations resulting from E. coli infection in chickens, following IBV infections are airsacculitis and systemic colibacillosis.
- Kidney damage: Some strains of IBV are nephrogenic, meaning that after replicating in the bird’s trachea (and causing respiratory disease), the virus will then spread to the kidneys (causing nephritis—or inflammation of the kidneys). Nephritis results in damage to the kidneys which often leads to renal failure and increases the risk of birds developing gout. Typical signs of renal failure include: increased water intake, rapid weight loss, and diarrhea in affected birds.
- Reproductive system damage: In both immature and adult egg laying hens, if the virus replicates in the oviduct, they are at risk of reproductive system damage. Affected hens may have reduced lifelong egg production and/or resulting in abnormal eggs that differ in shape (misshapen), size (smaller), internal egg yolk quality (watery), egg shell quality (rough or soft-shelled)
How Infectious Bronchitis is Diagnosed
Infectious bronchitis can be confirmed through several tests offered by most veterinary diagnostic laboratories. It consists of taking a simple swab from the chicken's trachea, and mailing it to the lab. Diagnostic tests include virus neutralization, haemagglutination inhibition and ELISA tests.
Transmission of Infectious Bronchitis Virus
The virus is transmitted via the respiratory secretions, as well as faecal droplets from infected poultry. Contaminated objects and utensils may aid transmission and spread of the virus from one flock to another. Recovered chickens can also spread the disease, as birds may shed the virus for up to 20 weeks after recovery from the infection.
Treatment of Infectious Bronchitis
Although infectious bronchitis is highly transmissible, most chickens will recover with supportive care. Since it's a virus, there is no treatment. However, antibiotics can help control secondary bacterial infections.