Few regions in the world are without IB virus
variants, he said. “In many countries, you have
three, four or five variants. We’re realizing 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, De Wit said.
Low Titers = 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
titers, 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%.
A group vaccinated at 3 and 16 weeks of age with a killed IB vaccine but no live primer had a drop in egg production of about 30%, while a group vaccinated with a live IB Massachusetts-strain vaccine at 3 weeks of age then with a different live IB Massachusetts-strain vaccine at 16 weeks of age had about a 10% drop in egg production.
Even better results occurred in birds vaccinated once with a live IB vaccine at 3 weeks of age, followed by an inactivated IB vaccine at 15 weeks of age. This group had no drop in egg production, he said.
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
“The lowest level of virus-neutralizing 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,” De Wit said.
Broad, Heterologous Bosting
“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,”
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 programs, 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, De Wit noted, “Producers quite often complain that vaccination isn’t working because there’s still a drop in egg production of about 5%, but without vaccination, that drop could have been 50%, 60%, 70% or even 80%.”
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, De Wit emphasized. 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.
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 titers 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 program 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, 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.