Few regions in the world are without IB virus variants, Dr De Wit said. “In many countries, you have three, four or five variants. We’re realising that it may be futile to vaccinate against one specific IB virus strain. You have to try and make smart vaccine combinations so your protection is broader.”

While IB variants can cause respiratory disease, the greater concern in layers is a drop in egg production and poor egg quality; in breeders, a drop in hatchability might also occur. False layers and nephritis are other possible consequences of IB, Dr De Wit said.

Low Titres = Poor Protection

Because they are long-lived birds, layers and breeders need long-term IB protection. Live IB vaccines can provide good protection but only for a short period of time; they result in low antibody titres, which correlate with low protection during the laying period. Killed vaccines are required for long-term protection but work much better if they are administered after birds have received a live vaccine first as a primer, he explained.

De Wit cited published, controlled studies conducted by other investigators demonstrating that layers not vaccinated against IB have the most severe drop in egg production – above 70 per cent.

A group vaccinated at three and 16 weeks of age with a killed IB vaccine but no live primer had a drop in egg production of about 30 per cent, while a group vaccinated with a live IB Massachusetts-strain vaccine at three weeks of age then with a different live IB Massachusetts-strain vaccine at 16 weeks of age had about a 10 per cent drop in egg production.

Even better results occurred in birds vaccinated once with a live IB vaccine at three weeks of age, followed by an inactivated IB vaccine at 15 weeks of age. This group had no drop in egg production, he said.

Dr De Wit also presented the results of studies he and colleagues conducted testing four IB vaccine combinations against four Chinese Q1 IB strains obtained from Latin America in 2009 and 2010. The primer was either a live Massachusetts (Ma5) IB strain or Ma5 plus a live IB 4/91 variant, which is prevalent in Europe, followed by killed boosters with IB M41 alone or with IB D274 (Table 1).

“The lowest level of virus-neutralising antibodies against this Q1 strain occurred when only a live Massachusetts-strain (Ma5) vaccine and a boost with inactivated M41 was used. On average, the most complicated system of broad, live-vaccine priming then a broad-boosting killed vaccine had the best results and yielded the highest level of neutralizing antibodies,” Dr De Wit said (Figure 1).

Figure 1. Mean virus-neutralising titres (log₂) against four strains of Chinese Q1 infectious bronchitis (IB) virus after boosting with killed IB vaccines

Broad, Heterologous Boosting

“There are exceptions, but the message is usually the same. It’s highly recommended, especially in areas with a high IB challenge, that inactivated vaccines be used to get more protection against IB and, in general, that more vaccine strains be used to achieve broad, heterologous boosting,” Dr De Wit said.

He also advised using a good, live, priming vaccine before killed vaccines are administered to increase the efficiency of the killed vaccines.

Even though good IB protection requires more complicated vaccine programmes, the good news, he said, is that not every IB variant needs a vaccine specifically for that variant. “By making smart vaccine combinations, you can solve your problems with a few vaccines.”

In addition, Dr De Wit noted, “Producers quite often complain that vaccination isn’t working because there’s still a drop in egg production of about five per cent, but without vaccination, that drop could have been 50 per cent, 60 per cent, 70 per cent or even 80 per cent.”

Vaccine Efficacy

Efficacy with IB vaccines, he pointed out, will be affected by the strains of IB virus that are administered, by the quality of each antigen per dose and by the adjuvants used in each vaccine.

Proper vaccine application is imperative, Dr De Wit emphasised. In addition, trials conducted with live IB vaccines have demonstrated that efficacy improves if the ventilation system is turned off and the lights are on. If the vaccine is administered in water, there needs to be good water quality, low in temperature and free of pathogens.

“Keep in mind that you are working with a very sensitive virus that’s easy to kill. If you’re aware of that, you’re on the path to better results,” he said.

Diagnostics

Dr De Wit is a ‘big fan’ of diagnostics when IB is suspected. “Even if there are no problems, I think it’s a good idea to obtain serological testing at the end of each flock just to see if titres are high for IB, because that means there was a challenge.”

It also means that the vaccination schedule was working. The information can help producers decide whether they should continue doing what they’re doing, or that their programme needs adjusting, he said.

Certainly, he said, samples should be taken for testing when there are clinical problems. “It’s very, very easy to make incorrect conclusions if you don’t obtain diagnostics. Maybe it’s not IB or it’s some unexpected variant. If you don’t know that, plans for the next flock will be wrong.”

Asked about the role of co-existing disease, Dr De Wit said that flocks with infections such as mycoplasma, pneumovirus or other health problems are not necessarily more susceptible to IB – but the clinical signs after the IB infection will be more severe and the recovery will be harder.

Further Reading

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Find out more information on infectious bronchitis by clicking here.