Infectious bronchitis virus (IBV) is an avian gammacoronavirus that only causes disease in chickens, although the virus has also been found in pheasants and peafowl, which may be subclinically infected. The virus is worldwide in distribution, and there are many antigenic types that can cocirculate in a given region. Some IBV types are widespread, whereas others are regional.
IBV is shed by infected chickens in respiratory discharges and feces, and it can be spread by aerosol, ingestion of contaminated feed and water, and contact with contaminated equipment and clothing. Naturally infected chickens and those vaccinated with live IBV may shed virus intermittently for up to 20 weeks after infection. The incubation period is generally 24–48 hours, with the peak in excretion of virus from the respiratory tract lasting 3–5 days after infection.
The severity of disease and the body systems involved are influenced by:
- strain of the virus
- age, strain, immune status, and diet of the chicken
- cold stress
Infectious Bronchitis is a major disease with a global presence which causes different challenges. Infectious Bronchitis is caused by the Avian Coronavirus. The virus is classified into different Genotypes, but the Genotype classification does not give us the full picture. Another classification is the serotype, as the serotype is the reaction between a specific antibody and a virus strain, but the serotype does not provide a complete immunological classification either, as different serotypes do not have full cross-protection between them. The variation of IBV serotypes is related to the variation of the S protein (Cavanagh, 1998), however nor does this provide the complete profile of the virus, as there is partial cross-protection between the different serotypes. The most widely used classification method is the protectotype (immunotype). The protectotype is the combination of different serotypes of the virus providing a broader protection than just the serotype vaccinated.
Aim of vaccination against Infectious Bronchitis
It is important to establish the purpose of vaccination.
Broilers – Vaccination is focused on reducing the economic losses caused by IB infections as these are reflected in weight loss and general poor performance of the flock.
Layers and breeders – The aim of vaccination is to protect the oviduct as IB infections may result in false layers, drops in production and changes in the internal and external quality of the eggs.
In this context vaccination of young chickens is often done at an early age (first day(s) of life), and especially in broilers focusing on inducing enough protection so as to cover the whole fattening period. In layers and breeders the programs are focused in protecting the oviduct during the first weeks of life with modified live attenuated vaccines. Later on during the production period immunity needs to be broad and long lasting, and inactivated vaccines are often used.
Timing of vaccinations
In general it is recommended to allow two weeks between two live IB vaccinations. To obtain a good booster effect of the inactivated vaccines preferably 4–6 weeks should elapse between the last live vaccination and the application of the inactivated vaccine.
If variant IB strains are not present, or if they are present but fall under the protectotype of the Massachusetts serotype, then a program based on this serotype can be used. If not, broader protection can be obtained by including vaccines belonging to other serotypes (such as vaccines containing serotypes 4/91) in the program.
It is not always obligatory to include a live and inactivated vaccine of the same type in the program. Some live vaccine viruses will be effective in priming birds for heterologous IB components in the inactivated vaccine and a cross reaction will occur resulting in stimulation of immunity to heterologous IBVs and therefore providing cross protection. This is for example the case after the use of vaccines with serotype 4/91. When followed by an inactivated vaccine containing a strain of the Massachusetts serotype, a cross reaction will result in high levels of neutralizing antibodies not only against the Massachusetts serotype but also against the 4/91 serotype, and against some other IB serotypes as well.
Prices of Chicken Bronchitis Vaccine