“You have to know the nature of
the field challenge to design a
vaccination program capable of
protecting,” says Richard Currie,
PhD, BVM&S, MRCVS, president
of x-OvO Limited, Scotland, a
biotechnology company that
performs diagnostics for many
poultry companies in Europe.
“In addition, to be cost effective,
you want to use as many
vaccines as you need — but
not more than you need. Appropriate
molecular diagnosis of IB
infections gives you that option,”
he says.
Complicated Diagnosis
The diagnosis of IB infection is
complicated, in part, Currie
explains, because of many
diverse IB viruses present in
the field. IB is an RNA virus and
RNA viruses easily undergo
genetic changes.
Testing for IB viruses is also an
expense, and in the current
economic climate, many
producers often prefer to limit
costs until a major clinical
problem occurs. When producers
do request IB diagnostic
tests, they usually opt for
serological-based tests that are
conducted on a more or less
routine basis, but the sample
sizes tested make this of
relatively limited diagnostic
value, he says.
New, pre-packaged polymerase
chain reaction (PCR) tests can
reveal whether a particular
subtype of IB is present, but
they can’t differentiate between
vaccine and field strains nor can
they identify emerging new
IB strains. “You can only find
what you know already exists,”
Currie says.
‘Indispensible’ testing
In contrast, molecular investigation
using real-time quantitative
PCR testing plus sequencing of
the S1 gene of IB virus not only
allows specific identification of
the virus that is present, it also
provides several practical ways
that veterinarians can alter
the way a flock is managed to
optimize health status and
performance, he says.
“In fact,” Currie says, “there are
poultry veterinarians who
now consider PCR testing an
indispensable part of their
clinical approach to IB.”
The newer technology makes it
possible to identify novel IB
viruses, determine the quantity
of IB virus present and compare
the efficacy of different vaccine
application methods.
Studies by x-OvO, in collaboration
with MSD Animal Health,
have demonstrated that more IB
vaccine virus replicates in birds
vaccinated by the spray route
compared to administration of
the vaccine in water, Currie says.
By comparing sequences of
commercial IB vaccine strains to
those in the field, it’s possible to
determine if an IB field strain is
identical to a vaccine IB strain
or different in a defined way,
he continues.
“These differences can be
significant because there are
specific changes that are
associated with a breakthrough
in vaccine protection. Hence,
the presence of these types of viruses can indicate to the
veterinarian that a stronger,
broader-protective vaccination
strategy is more appropriate,”
Currie says.
The resulting information can
help veterinarians determine
if flocks would benefit from
using a combination vaccine
approach, such as Nobilis IB
Ma5, which is based on the
Massachusetts IB serotype, and
Nobilis IB 4/91, which is based
on the IB 4/91 variant serotype,
he adds.
Monitors trends
The newer molecular technology
now used by x-OvO also
makes it possible to identify
important trends in the field
that can guide poultry
veterinarians and producers,
according to Currie.
It enabled the first diagnosis
of the Chinese IB QX-variant
genotype outbreak and
subsequent epidemic in the UK.
“This would have been missed
with the previous technologies,”
he says, noting that trends in the
IB viruses circulating tend to be the same whether it’s the layer,
breeder or broiler segment of
the market in a given area.
The technology made it possible
to demonstrate that suspected
field outbreaks of IB QX in
German flocks vaccinated
against IB QX with a live QX
vaccine were due to QX field
infection — not simply to the
detection of the live QX vaccine.
“Older technologies would
simply have confirmed the
presence of IB QX and everyone
would have thought it was the
vaccine,” Currie says.
For French flocks, the combination
of PCR testing and
extensive IB hemagglutination
testing of sera samples clearly
showed the presence of an IB
4/91 serotype field challenge in
flocks vaccinated only with an
IB H120 vaccine. “This is a good
application of the technology,
clarifying serological results with
a molecular confirmation test,
and it justified the need for
changing the vaccination
program,” he says.
The technology further demonstrated
that the IB Italian 02
variant, which was a major
problem in the EU some 8 years ago, has almost disappeared
from the area, he notes.
Testing with service package
Another advantage, Currie says,
is that veterinarians who collaborate
with certain animal health
companies, such as MSD Animal
Health, gain access to molecular
diagnostics as part of a service
strategy that supports appropriate
vaccine use.
For molecular diagnostics,
x-OvO prefers that tracheal and
cloacal swabs be submitted;
they provide larger amounts of
intact viral RNA, and the company
can provide the permits
necessary for sending clinical
material for testing, he says.
FTA cards can be used for
submission of samples from
countries where the export of
genetic material is not allowed
by local authorities; the cards
inactivate and stabilize genetic
material, but the technique
required to remove RNA from
the cards can sometimes
lower diagnostic sensitivity,
Currie says.
If uncomplicated testing is all
that’s required, which is the case with most submissions, results
are guaranteed a maximum of
21 days from submission; they
come with an analytical report
that puts the results into a clinical
context that veterinarians
can use. Sometimes, when dual
infections are involved, further
analyses may be necessary and
the results are sent as they
become available, Currie says.
The goal is to customize the
format of the results so they
emphasize issues that are
critical to the client.
There’s another important
benefit that advanced molecular
technology brings to the poultry
industry, he says. With the
tracking abilities it affords, the
technology can help define the
epidemiology of IB viruses in a
certain region or country, which
enables the poultry industry
to make better use of the IB
vaccines that are available and
tailor vaccination protocols
as needed.
Additional information about
x-OvO Limited’s diagnostic
services is available on the
company’s website at
x-ovo.com.
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