Infectious Bronchitis In Chickens

For the last few months I’ve been chatting online with Nancy, a Bitchin’ Chickens follower about various health issues within her flock: mites, lice, bumblefoot and a chick with curled toes. When her rooster died, I encouraged her to send him off for a necropsy. The pathologist confirmed my suspicions that he died of gout. Nancy sent me the lab paperwork and I noticed that she had previously sent in two birds who had been diagnosed with Infectious Bronchitis (IB).

Professional necropsies are great in that they provide you with the cause of death and the lab work might give you an idea of any underlying or contagious pathogens in your flock. Unfortunately they are written in medical jargon and I needed a dictionary to put it in language that a layperson could understand. The other downside is there is no information about the implications of the diagnosis and what you should do going forward (e.g. are your other birds at risk). I guess they leave it to you to do your investigation, but so often you find contradictory information.

I know very little about IB and offered to do the legwork for Nancy so we could both learn more. The first thing I found out is IB is a coronavirus, which I thought was fitting given the timing of the current Covid 19 pandemic.

That little bit of trivia aside, the important things to know about IB are: it’s a common, highly contagious disease seen only in chickens that mostly presents in upper respiratory issues, but can spread to renal (kidney) and reproductive systems. The necropsy results on Nancy’s hens indicated that one had an inactive ovary and both had damage to their internal organs (i.e. liver, kidneys, spleen and heart) as well as gout.

All chickens are vulnerable, but chicks are more likely to be seriously affected. Infected birds usually develop symptoms within a day or two, are sick for the next three – four weeks and if they recover are infectious for the following 20 weeks. Older birds may develop resistance to infection.

Several types of vaccines are available; however there are many strains of the virus which make it difficult to control and even vaccinated birds can become infected.

Transmission

Inhaling aerosolized respiratory secretions
Sharing feeders and waterers contaminated with nasal secretions or poop
Chickens can shed the virus for up to 20 weeks once recovered

Chick with IB (Credit: Cornell U.)

Infectious Bronchitis

Symptoms

Sneezing, gasping, coughing, tracheal rales
Nasal discharge
Teary eyes
Sinusitis
Facial swelling
Decreased egg production
Irregular and wrinkled egg shells with watery albumen
Decreased appetite
Increased water intake
Ruffled feathers
Wet litter
Chicks: depressed, huddled, seek heat, slowed growth
Similar symptoms to Newcastle Disease, Infectious Laryngotrancheitis, low pathogenic Avian Influenza and Infectious Coryza.

Factors Affecting Outcomes

Strain: There are about 70 different strains of IBV with varying degrees of virulence from very mild to severe symptoms, including death.
Viral load: the actual amount of virus in the bird, which is directly related to its efficiency. A high viral load means IBV is more easily transmitted between birds.
Age: Respiratory symptoms tend to be more severe in younger birds and early infection can result in damage to a pullet’s developing reproductive tract.
Sex: For unknown reasons, males appear to be more vulnerable than females.
Breed: Broilers have more severe respiratory signs than layer birds.
Immunity: A bird’s immune status affects the trajectory of disease. Chicks can be protected for up to two weeks after hatch by maternal antibodies.
Environment: Various factors can contribute to more severe symptoms: high ammonia levels in the coop; too hot or too cold temperatures; poor air quality; overcrowding; wet litter; poor nutrition; poor water quality; or co-infection with other respiratory diseases or secondary bacterial infections.

Complications

IB damages the chicken’s respiratory epithelium, often predisposing young chicks to secondary infections with pathogenic bacteria such as E. coli (causing airsacculitis and colibacillosis ) and Mycoplasma Gallisepticum and Mycoplasma Synoviae.
Kidney damage: some strains replicate in the bird’s trachea (causing respiratory disease), then spread to the kidneys causing inflammation, renal failure and gout. Symptoms of kidney failure include: increased water intake, rapid weight loss and diarrhea in affected birds.
If the virus replicates in the oviduct, a hen is at risk of reproductive system damage: permanently reduced egg production; misshapen, smaller, soft-shelled or wrinkled eggs; watery albumen; egg yolk peritonitis.