“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.
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
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.
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.
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
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.