Infectious Bronchitis (IB) remains an economically significant viral disease affecting both broiler and layer producers in the UK, with some farmers reporting a 20-50% drop in egg production in layers, and a 20% increase in broiler mortality.
New strains of this virus can emerge over time as has been seen with the QX strain which has now been widely identified across the country. As there is a continued risk of the disease evolving further, it is more important than ever for poultry producers to consider measures which can be taken to limit the disease risk.
With a short incubation period, the IB virus can spread through the flock within 36 hours, transmitting by means of air droplets and in faeces. Birds can then continue to shed the virus for several weeks after clinical recovery, and the disease can also open the gateway for concurrent infection from other viruses and bacteria.
Katie Pitman, technical veterinary adviser at MSD Animal Health UK, discusses how the disease has evolved, and the basis of good IB control.
“Over the years, new variants of the IB virus have continued to emerge as a result of amino acid changes in part of the genome of the virus,” says Pitman.
“In the early 1990s, a variant known as IB 4-91 (793B) was recognised in Europe. This strain has continued to be a major cause of IB throughout the world. More recently, two other strains of the virus have emerged in Europe, IT-02 and QX. In 2008 the QX strain was first seen in commercial poultry in the UK.”
Until 2019, QX cases were predominantly reported in layer flocks. Although, the number of QX field viruses detected in the UK has mainly increased among broiler flocks, the virus still impacts all forms of poultry resulting in severe clinical signs.
“The virus targets the bird’s respiratory system and uro-genital tract, causing respiratory disease. Poultry infected with this virus can suffer from a drop in egg production in commercial layers and breeding stock, and an increase in mortality in broilers, resulting in huge financial losses for farmers. Egg production drops are usually most severe when the birds have concurrent disease.”
Preventing an outbreak of IB in poultry
Paired with good biosecurity, correctly administered vaccination is the mainstay of IB control, and vaccination programmes must be adapted to suit the demands of individual farms. “Before choosing a vaccination programme, considerations should include the age protection against IB is needed most, and which virus strains you want to target.
“Commercial layers and broiler breeders are primed with live vaccinations during rear, and receive an inactivated vaccination, before transfer to the layer site, which lengthens protection during lay. In areas where there is heavy infection pressure from IB, birds in lay may need additional protection from a live vaccination. This has increased in popularity as the number of birds per farm and new sites continue to increase in the UK, thereby increasing the potential disease challenge.
“Broilers will only receive live vaccines which induce effective local immune responses in the respiratory and uro-genital tract,” says Pitman.
Top tips to optimise vaccination efficacy
To ensure vaccinations work effectively, live vaccines should be stored in a clean fridge at a temperature of between two and eight degrees Celsius. It is, however, important to avoid contact between the back of the fridge and the vaccine as this could cause the vaccination to freeze and therefore be ineffective. The use of a data logger is recommended as this will constantly measure the maximum and minimum temperatures.
During preparation, the vaccine should be reconstituted in chlorine free water, as the chlorine from tap water will kill the live vaccine. Katie recommends the addition of a water stabiliser, such as Aviblue, Vac-safe or VacPac, as this will remove the chlorine from water before the vaccine is added to the solution. This should be enough to dechlorinate all the water that the birds will drink within two hours.
“When it comes to vaccinating chickens, producers can choose from two methods, either vaccinating using a spray, or in the drinking water,” she says.
Administration via the drinking water
“IB vaccines given in the drinking water is a more straightforward method of administration in layer flocks in a multi-tier system as it can be difficult to reach all birds with a sprayer. We would recommend priming the lines with the vaccine solution, so that the whole water line is full before allowing the birds to drink. It is easiest to vaccinate first thing in the morning when lights come on so that the vaccinated water is their first drink of the day.
“As a guide to help when calculating the correct stock solution, record the amount of water consumed within the first two hours of the day, once the lights are turned on, the day before the vaccine is due. An extra 10% water can be added to the stock solution to allow for losses when flushing the lines, or to compensate for a hot day where the birds might drink more.
“Finally, any sanitisers or acids added to the water should be switched off 48 hours before vaccination commences as these can affect vaccine efficacy. They can then be restarted 24 hours after the vaccination has finished,” says Pitman.
Administration via a spray:
As an alternative to administration through the drinking lines, another option for producers is applying the vaccine by spray, which would require investment in a sprayer. If possible, try to ensure that each site has its own spray equipment.
“Spray equipment must be clean and well maintained, with a consistent droplet size being applied across all birds. This can be checked on a concrete floor or on water sensitive paper.
“As the birds will be most settled during dark periods, it is advisable to treat early in the morning or last thing at night. This is also the coolest part of the day, so it is more comfortable for both the birds and the vaccinator,” she says.
“Lights should be switched off, or dimmed, to help ensure the birds are quiet. Fans must be switched off prior to commencing the vaccination and switched back on once spraying is completed. Enough water should be added to the sprayer to facilitate covering all birds twice.
“We would also advise doing a dummy run of the house, using plain water, if you are new to vaccinating, to time how long it would take to complete vaccination,” she says.
Deionised water can be used in the sprayer removing the need for water stabiliser. Once the vaccine is reconstituted, it should be used within two hours. Alternatively, a water stabiliser, such as those mentioned previously, can be added to tap water before addition of the vaccine.
Biosecurity top tips
“Viruses are easily spread within farms and between neighbouring sites. Therefore, it is vital to combine a vaccination programme with good biosecurity protocols to limit the spread of disease,” says Pitman.
“I’d recommend speaking to your vet to find the most appropriate vaccination regime for your farm, and couple this with the following practical measures to reduce disease risk.”
- Good flock management to minimise stress, as this can cause virus shedding.
- Change overalls and disinfect boots before entering each poultry shed, or where possible, use the same personnel for each shed
- Use pest control programmes to minimise rodents and insects which can spread disease
- Keep all pets and wild animals out of poultry houses
- Keep areas around the houses and feed bins clean
- Avoid contact with non-commercial poultry or wild birds
- Observe the flock regularly to recognise a change in behaviour and early signs of disease
- Ensure proper ventilation and litter moisture control
- Ensure thorough cleanout and disinfection of houses at turnaround
- Ensure all vehicles entering the farm follow wash-down procedures
- Limit visitors to the farm if possible, or ensure all visitors have been free from poultry for 24 hours and have access to PPE before entering
- Avoid sharing equipment between sites, as if the sprayers are not cleaned after use, they can transfer virus and bacteria to other sites
Recognising IB in poultry flocks
Birds of all ages are susceptible to the infection and although they could display different clinical signs there are often common signs including:
Gasping and coughing
A drop in egg quality and production
Misshapen or soft‐shelled eggs with watery content
Kidney damage leading to increased water intake, scouring and wet litter