Infectious Bronchitis (IB) is one of those viruses that likes to keep one step ahead of your birds, their vaccination programme and the boffins making the vaccines.
IB is a constantly moving target – a virus with an outer coat that can regularly change its spots such that the bird’s immune system fails to recognise all the different variations.
The virus was first properly identified some 80 years ago being described as a "new respiratory disease of baby chicks". Since then a whole range of IB variants (sometimes called serotypes or strains) have emerged. Some of these affected only one continent, others have spread around the world. Some appeared for a while, caused some problems and have never been seen again. Some, like a number of the so called "Dutch variants" of the late 1970s and early 1980s caused major problems, disappeared and then crept back over the last few years. More recently viruses such as 793B (also called 4/91 and CR88 – very exciting names!), have appeared, spread around the world and seem to be here to stay.
Controlling IB
Up until recently, control of these virus variants has tended to be a case of playing catch up – identifying new strains and then developing new vaccines or vaccination strategies to control the problem. Over the last few years, the approach has been different – trying to take a more holistic route, aiming to achieve the broadest and most effective possible protection in pullets by using a combination of the existing live IB vaccines, properly applied and well targeted. Evidence is that by using a combination of different strains of live IB vaccines in your rearing programme you can persuade the birds immune system to produce a very broad defence against quite a number of different variants. This has been the cornerstone of the approach to IB control for the last few years. It doesn’t always work though and the development of the 793B type vaccines was needed to specifically address that more aggressive and more unique virus strain.
The new kid on the block – QX/D388
Now we have a new kid on the block – IB QX, sometimes called Chinese QX. The name originated following outbreaks of disease in the Qingdao region in China, from which a novel strain of IB (termed QX) was isolated. Since that time the virus has crept towards Europe. From 2004, severe egg production issues have been identified with a very similar virus in parts of Western Europe, predominantly in the Netherlands, but also reported from Germany, France, Belgium and Denmark.
Disease has been reported in broilers and layers. In layers, the picture has been of poor peaks; sometimes flocks reaching only between 30 and 50% peak production – a disaster! The birds often appeared healthy and showed no hint of the problems to come. Once they reach productive age a proportion show very swollen abdomens resulting in a waddling, penguin like gait. These birds have massive accumulations of fluid in their abdomens in blocked oviducts (egg tubes) and will never come into production – the so called false layers, looking as if they are ready to lay, but they never will. Such flocks are clearly a disaster and there is then no way back.
So what is the cause?
The virus isolated from the Dutch cases was identified by the Dutch Research Institute at Deventer as a new strain that they called D388. The Chinese connection came from further tests which showed that the virus was 99% similar to the Chinese QX viruses.
So what about the UK?
There are several theories as to why UK flocks as yet have not been as severely as those across the Channel. We could rest on our laurels and suggest it is all down to our better disease biosecurity. There may be some truth in that in less densely populated poultry areas or regions of UK. Another theory is that it is just a matter of time and that the virus has not hopped on a ferry yet! That complacent view is now coming to an end as there is increasing evidence of the virus being present in UK flocks, initially small backyard flocks, but increasingly in commercial flocks. Some health issues in broilers have been linked to demonstration of the QX/D388 virus. Surveys in UK laying flocks showing varying degrees of egg production problems have confirmed evidence of exposure to this new variant.
However, as we go to press there does not seem to be evidence of the severe false layer flocks in UK – yet! Some observers say this is never likely to occur because of our approach to IB vaccination over the last few years – our breeders passing on high levels of early protective immunity and rearers tailoring the combination live IB vaccine programmes. This view is somewhat reinforced by recent research in Italy and elsewhere that confirms that the combination of different live IB vaccines we already have, as advocated by UK poultry vets for some time, can be effective against laboratory challenges with the QX/D388 strain.
However, before we all sigh a huge sigh of relief our flocks may still be at risk. Research going back to the early 1970s showed that the pullets’ reproductive tract can be damaged by a whole range of fairly mild IB viruses in the first week of life as chicks, so there is always a danger of an IB virus getting in early and causing problems.
So what can we do?
The answer is to stay one step ahead of the game and ensure that your laying flocks are protected from day one. How do we achieve this? Firstly, the breed companies spend a lot of time devising vaccination programmes that not only protect their flocks against disease issues in their laying life but just as importantly providing the day old layer chick with its own little package of protection – so called maternal antibody. This includes diseases such as Gumboro, Salmonella, Mareks, Newcastle Disease and importantly here, IB. The chick’s yolk sac is packed with these antibodies. However, these are short lived and are rapidly used up, lasting the chick only a few weeks, so it is important to supplement this with early live IB vaccines given to the chick to trigger the chick into producing its own supply of protective antibodies. This will usually start with day old spray vaccination in the hatchery.
Whilst the chicks are responding to these vaccines, high standards of biosecurity will prevent birds being exposed to dangerous bugs at the most critical and susceptible periods until immunity is strong enough.
Partnership counts!
For most producers taking delivery of point of lay pullets all the hard work will have been done by the breeders, the hatcheries and the pullet rearers. They are currently beavering away to provide you and your birds with the best possible protection. This should prevent UK flocks from suffering the worst excesses of the "false layer" syndrome seen elsewhere.
It is another example of the strengths of UK poultry production – early warning systems by poultry vets to what is lurking away from our shores, vaccine companies alert to the need to consider producing new variant vaccines or demonstrating that the current weapons in our armoury, properly applied, work, breeding companies and pullet rearers producing point of lay birds "fit for purpose" and egg producers aware of their responsibilities in getting the best out of the Rolls Royce birds they are being supplied with.
All this requires hard work, investment and effective communication at all stages of the chain to make sure that the new kids on the block do not wreak havoc in our flocks.
Stephen Lister, Claire Knott, Philip Hammond & Ian Lowery
Crowshall Veterinary Services
