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D388 ‘highly pathogenic’ in layers, broiler breeders

The D388 variant strain of the infectious bronchitis (IB) virus is highly pathogenic in layers and broiler breeders, but protection can be achieved with broad heterologous vaccination, Dutch investigators say.

The investigators conducted studies to gather advice for the Dutch poultry industry; it has suffered considerable damage due to infections caused by the D388 strain of the IB virus, which is derived from the IB QX genotype, says Sjaak De Wit, DVM,PhD, Animal Health Service, the Netherlands, and colleagues.

They tested several vaccination programs in young, specific-pathogen-free layers, in young layers with maternally derived antibodies against D388 and in young commercial broiler breeders, The results confirmed field observations that D388 of the QX genotype is able to cause cystic oviducts in a high percentage of birds,l mortality due to nephritis and respiratory distress with complete tracheal cilostasis and airsaccultis.

Vaccination programs using different combinations of heterologous live vaccines at day 0 or at days 0 and 14 induced a reasonable to high level of protection after challenge with D388 at 28 days of age.

However, “for very early protection, maternally derived D388-neutralizing antibodies were shown to be very important,” and could be achieved by using a broad, heterologous live, priming vaccine followed by boosting with inactivated IB virus vaccines containing two or three heterologous IB virus antigens, they say in the October 2011 issue of Avian Pathology.

Swedish studies show evolution of IB viruses

Swedish investigators say they have demonstrated that infectious bronchitis (IB) viruses are constantly evolving, underscoring the need for careful monitoring of IB trends.

In Sweden, IB in layers has been associated with a drop in egg production and thin eggshells, as well as poor growth in broilers. When the investigators sequenced selected isolates from some of the IB cases using conventional real-time polymerase chain reaction (PCR) they found the isolates were over 98% genetically similar to strains of the IB QX-like genotype.

Further analysis showed that Massachusetts-type strains of IB virus that were predominant in the 1990's had been replaced by D388/QX like strains, but the evolutionary link could not be established. "Remarkably, a strong positive selection pressure was determined, mostly involving the S1 subunit of the S gene" resulting in recombination events, says S.H. Abro, Swedish University of Agricultural Sciences and the National Veterinary Institute, Uppsala.

In addition, two new isolates generated from recombination were found, diverging from the D388/QX-like-branch and indicating the emergence of a new lineage, they say in the September 2011 issue of Veterinary Microbiology

Novel QX IB virus strain found in Southern England

A novel QX-like strain of the infectious bronchitis (IB) virus is co-circulating with previously described QX viruses on a commercial layer farm in Southern England, resulting in lost egg production and nephritis, investigators reported at the World Veterinary Poultry Association Congress held in Cancun, Mexico.

Molecular analysis of the strain, which was found during routine monitoring for IB viruses, revealed several substitutions in the major antigenic protein of the virus, said Isabella Monne, DVM, Istituto Zooprofilattico Sperimentale delle Venezie, Italy.

The results raise questions about the potential antigenic divergence of the new strain from other IB QX strains and the vaccination programs that will offer the best clinical protection, she said, noting that more surveillance will be needed to determine if this novel strain is spreading throughout the country.

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