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Further analysis showed that Massachusetts-type strains of IB virus that were predominant in the 1990's had been replaced by D388/QX like strains, but the evolutionary link could not be established.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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