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Test Results Show Growing Prevalence of IB 793B (4/91) 4 over Five Years

by 5m Editor
25 May 2012, at 12:00am

A five–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 specialises in veterinary biological analysis in the Journal of Poultry Respiratory Protection from Merck Animal Health, US.

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 per cent tested positive (Table 1).

Table 1. Percentage of layer and breeder samples positive for IB virus
Year Number of samples tested Percent positive for IB virus
2006 51 47
2007 76 41
2008 71 49
2009 99 55
2010 32 34

In 2010, the number of positive tests tapered off to 34 per cent, but Dr 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 Dr 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.

Table 2. Percent of samples positive for IB virus strains in layers and breeders when both single and multiple iB virus isolations are considered
Year 793B MA QX
2006 50% 17% 8%
2007 58% 26% 10%
2008 54% 6% 18%
2009 46% 22% 6%
2010 64% 18% 9%

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, Dr Robineau said, 81 per cent were positive for IB virus in 2010, up from 76 per cent 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 three years (Table 3).

Table 3. Percent of samples positive for IB virus strains in broilers when both single and multiple IB virus isolations are considered
Year 793B MA QX
2006 44% 38% 24%
2007 71% 38% 49%
2008 68% 30% 33%
2009 53% 39% 21%
2010 45% 32% 5%

Sentinel Layer Study

To assess further 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.

Improved Results

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.

Table 4. Results of study comparing conventional to updated vaccination plan for broilers
Year Number of flocks Losses Condemnations Viability Age at slaughter
(days)
2007-2008 (conventional vaccine plan) 70 3.12% 0.77% 96.11% 42.22
2010-2011 (updated vaccine plan) 54 2.84% 0.55% 96.61% 41.39

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, Dr 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 concluded.

Further Reading

- Find out more information on infectious bronchitis by clicking here.


May 2012