Disease Spotlight
30 Jul 2025
Introduction
Infectious Bronchitis is an infectious, rapidly spreading respiratory virus of chickens. Similar to the common cold of humans, it has a high mutation rate which results in more types of IBV arising each year. The virus is introduced into the respiratory tract before replicating and producing lesions in other organs such as kidneys, oviduct and the proventriculus and gizzard. The incubation period is short, only requiring 1-3 days before rapid bird to bird transmission can occur.
Clinical Signs
Infectious Bronchitis is a silent beast in the egg laying community, often being overshadowed by clinical signs resulting from secondary infections of E.coli and Mycoplasma. As a result, the clinical signs are highly variable depending on the strain of IBV, and the presence of co-infections.
The most notable clinical signs of an uncomplicated IBV infection include:
Up to 20% decrease in feed intake, followed by a 10-20% drop in egg production.
Decrease in egg quality
Loss of shell colour and strength
Albumen is thinner with potentially more meat/blood spots
Flocks will be lethargic, quiet and will reduce their ranging and nesting behaviour resulting in higher floor/system egg numbers and more dirty eggs.
Respiratory signs in the very early stages of disease can occur, with red eyes and sneezing being most commonly reported clinical signs.
Mortality is rare unless a coinfection is present.
It is exceptionally common for post-mortem to reveal secondary infections, presenting as egg peritonitis, nephritis, gout and/or inflamed ovaries with damaged follicles.
It is exceptionally common for post-mortem to reveal secondary infections, presenting as egg peritonitis, nephritis, gout and/or inflamed ovaries with damaged follicles.

Diagnostic
A good diagnostic approach is required to determine the effect of clinical or subclinical IBV infections. This usually results in multiple sampling points in order to create a history and reduce the risk of missing the initial outbreak. A combination of tests is required to get the ‘full picture’.
Diagnostics available:

PCR Viral isolation with typing of Isolation of the virus from the respiratory tract is likely during the early stages of an IBV infection. Within a few days of the initial outbreak the virus has progressed from the respiratory system and so isolation from kidney, faeces or the caecal tonsil is recommended.
Seroconversation by blood analysis
Does not have the ability to differentiate between variant strains but can provide a picture of exposure to IBV virus. The antibody titres must be interpreted with care as it can be influenced by
Age of vaccination and vaccination program
Interval between vaccine administrations
Interval between vaccination and sampling.
Best practice is to take routine IBV bloods at regular intervals throughout lay to establish a baseline, so if there is an IBV outbreak you have comparison serology to look back on.
To work on a treatment plan please reach out to the Hatch House Veterinarians through our contact page. We stand ready to help you with your animal health needs.
Written by Hatch House Senior Veterinarian
Alex-Kate Langfield BVetBiol/BVSc