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FlockChek* Infectious Bronchitis Disease Antibody Test
Kit
Infectious bronchitis virus (IBV) is a highly contagious viral
disease of chickens, usually manifested as a respiratory condition,
and may cause high mortality rates in young flocks or poorly
protected flocks. An assessment of immune status, as well as
serological identification of presence in the field of IBV, requires
a measurement of antibodies to IBV in serum.
This ELISA assay is designed to measure the level of antibody to
IBV in commercial poultry flocks. Conventional immune status
profiling was often done using hemagglutination inhibition (HI). The
FlockChek* Infectious Bronchitis Disease Antibody Test Kit provides
a sensitive and specific method of antibody quantification. The
assay can be performed in less than two hours, greatly reducing the
time required for serological detection of IBV vaccine immune
response or field-challenge exposure. The vaccine response in
broilers can be monitored by establishing baseline titer ranges at
either 35 days of age or by using paired samples with bleeds taken
at 35 days of age and at the processing plant. This titer data can
be used to help define the dynamics of a field exposure and the
interaction with the current vaccination program.
The vaccine response in broiler breeders and commercial layers
can be monitored by routine bleeding of flocks to assess the decay
of maternal antibodies and the vaccination program. Following live
vaccination, flocks should be sampled at 5–6 weeks of age, 10
weeks of age, and then 4–5 weeks post-vaccination with the
inactivated vaccine. Further testing dates are at 25–30 weeks
of age, 45 weeks of age and 55–60 weeks of age. The duration of
the immunity should be determined, as well as the coefficient of
variation (CV) in titer for the flock and the interactions of field
IBV exposure. These three parameters correlate with production
performance and clinical conditions.
xChek* is an effective tool to store flock information in a
database format when the initial assay is performed. Data can be
retrieved and explained in different graphic and report formats
using flock identification, farm, etc. Data from a flock that has
been monitored for vaccine immune response to IBV can be presented
as a histogram, which reports flock identification, test date,
number of samples tested, mean titer and CV, along with a bar graph
representing the number of birds whose titers fall within each of
the particular titer groups.
Testing flocks that receive the same vaccination program, and
comparing the level and variability in titer from flock-to-flock can
also be done to check the efficacy of vaccine administration. A
homogenous immune response to vaccination typically shows a CV of
less than 40–60%. Improper administration of vaccines has been
shown to increase the CV in the flock. A flock with higher than 60%
CV indicates that there are birds in the flock with little or no
response, in addition to birds with a high or adequate response to
vaccination. Using xChek, you can compare on a flock-to-flock basis,
or with previous flocks using the same vaccination program, or any
other variations in vaccine methodology, such as drinking water vs.
spray or different droplet sizes (coarse spray vs. fine spray). The
use of printed reports and histograms makes the site-by-site and
vaccine variable comparisons easy. Establishing baselines is easily
accomplished using the baseline feature in the xChek software. The
software facilitates the choice of flocks to be included in your
baseline, and automatically calculates the normal mean titer for all
of the flocks selected, the minimum and maximum titer within flocks
selected, and the variability between flocks.
At the processing plant, flocks should be sampled randomly (15
samples per flock) each day and identified by locations, complex,
farm and house. At the end of the week, these samples should be
screened for IBV antibody. Over a period of six months to one year,
a baseline is established for what is a "normal" or expected IBV
titer in a geographic area, complex, farm, etc. Changes in flock
data as testing continues will flag potential problems that may be
developing in particular farms or broiler complexes. This can help
in updating the biosecurity measures to reduce field-challenge
pressure, as well as any changes in the vaccination programs
regarding vaccine strains—day of vaccination, adding a booster,
changes in the vaccine application methodology, etc. Seasonal
changes in titer can also be tracked using processing-plant
monitoring.
Graph 1 shows the level of FlockChek Infectious Bronchitis
Disease Antibody Test Kit for high, medium and low titers.
Low IBV titers are common in low IBV-challenged areas, where the
H-120 strain is used for the control of IBV challenge that is more
closely related to Massachusetts type of strains. These mean titers
need to be analyzed for the coefficient of variation (CV), where
medium CVs (40–60%) are associated with a good uniform
application of vaccination. High CVs with low titers are suggestive
of a need to improve the vaccine application, while a low CV with a
medium titer can be related to a recent field-challenge exposure. A
low CV with high titers needs to be correlated with the clinical
condition of the flock, and improvements in the biosecurity measures
need to be made, but also can be related to the vaccines themselves
(i.e., "rolling factor"). Medium titers with a medium CV may be an
indication of IBV-challenged situations where the flocks were
properly vaccinated, but biosecurity measures allowed repeated
exposure on the farm. These cases are typically seen in all-out
farms, where the virus circulation level is more under control. A
low CV with these types of titers can also be associated with an
early challenge, but the titer will often be observed in the upper
level of the medium titer ranges. Recycling of litter, a common
practice on farms in the U.S., allows for high pressure from the
vaccines themselves (such as Arkansas strains), driving the baseline
to a higher level.
In Europe, titers expected at the processing plant from flocks
without IBV problems run about 500–1,000 ELISA titers on IDEXX
IBV kits. But in some areas in the U.S., titers expected for IBV at
the processing plant can be between 4,000 and 5,000. These high
titers are related to a good vaccine immune response and the
interaction with residual IBV on the farm. Based on field
experiences, veterinarians have established criteria for
interpretation of the FlockChek Infectious Bronchitis Disease
Antibody Test Kit. For example, if the IBV titers are 5,000 to
10,000, the IBV problem in the farm is most likely related to IBV
strains that are similar to the live vaccines used in the field. The
vaccines themselves should be ruled out if a poor application was
performed, and/or if the live vaccines are rolling and "heating up"
the titer on the farm.
High titers between 12,000 and 20,000 are usually related with
field challenge where variant IBV strains, (rather than those used
in the live vaccination program) are likely to be present on the
farm. When broiler breeders and/or commercial layers using
inactivated vaccines are still facing continuous IBV field pressure,
titers are observed to be high and the CV will change according to
the timing of the field challenge and the age that the samples were
taken.
Graph 2 shows the performance of different commercial ELISAs for
IBV. They vary in range of titers and accuracy to indicate and
differentiate vaccine immune response vs. field IBV-challenge. The
IDEXX FlockChek Infectious Bronchitis Disease Antibody Test Kit
nicely distinguishes between low, medium and high titers. This adds
value for production veterinarians in recognizing when a farm is
heating up under field challenge, when inadequate vaccine
application was performed or when a rolling reaction by the live
vaccines is causing high condemnations and respiratory problems.
Flocks showing titers higher than 10,000 up to 20,000 are candidates
to perform IBV PCR assays for serotyping because there probably is
another strain of IBV that is not matched by the live or inactivated
vaccine strains used in the vaccine program. This will also allow
the veterinarians to apply preventive medicine to minimize the
economical consequences of the clinical disease and secondary
bacteria contamination on the farm.
Graph 2. Low, Medium and High Titers from FlockChek
Infectious Bronchitis Antibody Test Kit and Three Other Commercially
Available ELISAs for IBV
Serum samples that were known as low, medium and high titers for
IBV were analyzed in four commercially available ELISAs for IBV. The
graph shows good expanded dynamic range in a meaningful area, such
as the medium to high titers that can give a better comprehensive
field interpretation.
This study showed that:
- Every ELISA for IBV has a different definition of medium and
high titers. This means that baselines between these four products
can be different, especially to interpret medium and high titers.
Titer information from one kit is not directly applicable to other
IBV kits.
- The IDEXX FlockChek* Infectious Bronchitis Antibody Test Kit
has a good separation between low, medium and high titers. This is
an important aspect in the sensitivity of detecting real field
challenge and not misleading the production veterinarian in the
interpretation of results.
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In Poultry Testing
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