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Infectious Bronchitis

Other Names: Avian Infectious Bronchitis, Chicken Coronavirus

Infectious bronchitis (IB) is an acute, highly contagious respiratory disease of chickens, caused by the infectious bronchitis virus (IBV), a type of coronavirus. There are several different serotypes and strains of the IBV, which are found worldwide.

IBV infection initially occurs in the respiratory tract, with the trachea being the primary target. It remains there for about a week, where it replicates and causes varying amounts of damage to the epithelium, predisposing birds to secondary infections with pathogenic bacteria, especially E. coli and Mycoplasma.

Depending on the strain of the virus, it may migrate from the trachea to other areas of the chicken's body, most commonly, the kidneys, reproductive system (hen's oviduct and rooster's testes), or alimentary tract.

Transmission


IB virus is acquired through inhalation or direct contact with infected birds or indirectly through exposure to a contaminated environment. Droplets containing the virus are expelled during coughing or sneezing, and shed in the feces or on the eggs, from infected birds. The virus is not transmittable from hen to chick through the egg. Once recovered, chickens may remain carriers and shed the virus for up to 15-20 weeks.

Disease Course


IB has a short incubation period. In an affected flock, all the birds will typically develop clinical signs within 24 to 48 hours. Clinical disease will usually last for 7 days.

Clinical signs


Clinical signs include watery or frothy exudate in the eyes, coughing, tracheal rales, nasal discharge, and sneezing. Young chicks usually appear depressed and huddle near a heat source. In some cases they may develop severe respiratory distress. Infection in very young chicks may result in the development of cystic oviducts.

Adult hens actively laying eggs often develop a sudden drop in egg production lasting for 10 to 14 days. They may also lay thin, wrinkled or roughened egg shells with thin, watery albumen. Loss of pigment in brown-shelled eggs is common.
Uncomplicated cases of the respiratory disease usually resolve within a couple weeks. However, the damage to the respiratory system caused by the infection often results in complicated co-infections with opportunistic bacteria. In addition, depending on the strain of the virus, after the virus replicates in the trachea, it will spread to other organs. If it spreads to the kidneys, affected birds often develop urolithiasis and renal failure. When it spreads to the reproductive organs, it can cause egg laying related complications and disorders.

Diagnosis


During the first week of infection, a trachea swab from the affected bird can be taken and sent to a veterinary diagnostic lab for confirmation of the IBV. After the first week, cloacal swabs are the preferred location. If the chicken has died, samples can be taken from the trachea, cecal tonsils, lung, kidney, testes or oviduct.

Prevention


There are several types of vaccines available against IBV, which are widely used by the commercial poultry industry. Laying hens and broiler breeders initially receive the live attenuated vaccine administered to young chicks en masse through sprays or via drinking water. Followed by the inactivated vaccine as a booster in 4-6 weeks.

Clinical Signs

Frothy exudate in the eyes
Rales
Sneezing
Coughing
Difficulty breathing
Nasal discharge
Drop in egg production
Thin, wrinkled or roughened egg shells
Loss of pigment color of eggshells
Watery albumin

Diagnosis

  • History
  • Clinical Signs
  • Laboratory testing

Reported Cases

  • Case 1: Infectious bronchitis in a Chicks A nephropathogenic strain of Infectious bronchitis virus (IBV) was the cause of high mortality in 2 to 3-week-old chicks. Approximately 100 out of 240 chicks died within a 1-week period. No respiratory signs were observed. All of the seven chicks necropsied had slightly enlarged, very pale kidneys with uratefflled ureters and diffuse, tan, fine stippling. Histologically, acute nephrosis and subacute interstial nephritis was found. The diagnosis was confirmed by virus isolation and PCR and the nephropathogenic aspect was demonstrated by finding abundant IBV antigen in the renal tubules and only small amount in the bronchial epithelium by immunohistochemistry. Ref

  • Case 2: Infectious Bronchitis in a Organic egg farm Infectious Bronchitis virus (IBV) infection was the cause of a reported reduction in egg production and egg shell quality in layers on a small organic egg farm. Diagnosis was based on positive serology titers in all hens and on one submitted hen that had salpingitis and oophoritis with positive IBV immunohistochemical staining. Ref

  • Case 3: Infectious bronchitis virus causing renal damage in a Laying hens Avian urolithiasis syndrome was diagnosed in 14-to-25-week-old chickens from a multiple-age caged-layer complex housing more than 2.5 million chickens. Losses from this syndrome ranged from 0.5 to 1.0% per week. Seven-to-14-week-old pullets from this facility had multifocal renal tubular necrosis leading to interstitial fibrosis, tophus formation, and tubular dilation. A coronavirus was isolated in embryos inoculated with pooled samples of trachea, kidney, and cecal tonsil of 4-week-old pullets. This virus, identified as 85-209, was related to infectious bronchitis virus strain Florida 88 by hemagglutination-inhibition assay. Day-old specific-pathogen-free chicks were inoculated with fifth-embryo-passage amnioallantoic fluid containing this virus. These chicks developed histologic lesions of tracheitis at 5 to 7 days postinoculation. Half the chicks inoculated by eyedrop developed renal tubular necrosis after 7 days. Urolithiasis in the flock investigated was attributed to renal damage by this strain of infectious bronchitis virus occurring in 4-to-7-week-old pullets and progressing to segmental atrophy, hyperplasia, and ureteral stone formation in 14-to-25-week-old chickens. Ref

Treatment

NameSummary
Supportive careMost birds will recover with supportive treatment. Isolate the bird from the flock and place in a safe, comfortable, warm location (your own chicken "intensive care unit") with easy access to water and food. Limit stress.
AntibioticsMay be indicated to control secondary bacterial infections.
St. John’s Wort (Hypericum perforatum) extract120 mg/kg showed significant antiviral effect on IBV in vitro and in vivo, respectively.Chen, Huijie, et al., 2019
Forsythoside A (Forsythia suspensa) extract80 mg/kg of feed showed an antiviral preventive and therapeutic effect against infectious bronchitis in chickens.X Wang et al., 2020

Support

Prevention

  • Vaccinate: There are several types of live and inactivated vaccines available, however the emergence of multiple strands of the virus have made control difficult.
  • Biosecurity
  • Quarantine new chickens before adding them to the flock.

Scientific References

Good Overviews

Age Range

All ages are susceptible but the disease is more severe in young chicks less than 6 weeks old.

Risk Factors

  • Poor biosecurity
  • Stressed and overcrowded birds