A 5-year summary of test results by a diagnostic
laboratory in Europe shows that infectious
bronchitis (IB) virus is clearly the most prevalent
respiratory disease among poultry, reported Brice
Robineau, DVM, of Finalab, which specializes in
veterinary biological analysis.
While the tests involved poultry flocks only in France — Europe’s top producer of chicken meat — the data provide a meaningful snapshot of the prevalence and diversity of the IB virus.
In 2009, the year with the greatest number of samples, more than half of layers and breeders tested were positive for IB virus. Between 2007 and 2010, an average of 45.2% tested positive.
In 2010, the number of positive tests tapered off to 34%, but Robineau said some of the samples submitted could not be typed, possibly because the virus is a new genotype not sensitive to polymerase chain reaction testing.
According to Robineau, the most common IB virus strain circulating is the variant 793B (Table 2), which first appeared in France in 2005. The 793B variant is of the same Protectotype as IB 4/91, which means it has cross-protective ability.
The next most often found IB virus strains were Massachusetts and the variant QX, he said, explaining that the study was based on samples sent by farmers or technicians who suspected infectious respiratory disease.
In broilers, Robineau said, 81% were positive for IB virus in 2010, up from 76% in 2009. Again, the majority of IB virus strains found were 793B,followed by the Massachusetts then QX IB virus strains, but the percentage positive for 793B was not as high as it was in the previous 3 years.
Sentinel Layer Study
To further assess the prevalence of IB viruses,
Finalab also conducted a study in 2011 using
sentinel birds involving six layer farms in France.
Between six to 10 specific-pathogen-free birds
were placed on each of the farms, which were all
contaminated with IB virus.
This study further demonstrated that 793B was the most prevalent IB virus circulating. It also showed that sentinel birds not vaccinated for IB were contaminated by the production birds, he said.
In a third study, Finalab compared two vaccination
protocols on five broiler farms with high IB pressure.
Protocol 1, used in 2007 and 2008, began with
a conventional IB H120 vaccine in the hatchery
and a booster at 14 days of age with IB virus 4/91
in the field. The H120 vaccine is based on the
Massachusetts IB serotype.
Beginning in 2009, the farms started transitioning to Protocol 2, which consisted of Ma5 (Massachusetts) and 4/91 vaccines administered at the hatchery. By 2010, all five farms were using Protocol 2. Several production parameters, such as condemnation and age at slaughter, were better with the updated vaccination plan (Table 4), while daily weight gain and the feed-conversion ratio was comparable between the two regimens, Robineau said.
The veterinarian concluded that for broilers in an area with high IB virus pressure due to 793B IB virus variant and possibly to the QX IB virus strain, “vaccination with H120 followed by field vaccination at 14 days can be replaced with vaccination that can be done in the hatchery to prevent the degradation of performance by IB virus contamination.
“What’s remarkable, in my opinion, is that the 793B virus has been very stable over the years,” he said.
For long-lived birds such as layers and breeders, Robineau said the vaccination plan would depend on the situation in a given area or on a given farm, but “our strategy is to use a lot of live vaccines providing broad protection, then to booster with inactivated vaccines.
“You have to get immunity very early, during the first weeks of life, to prevent damage to the reproductive tract. You have to use multiple variants and booster for them,” he said.