Download Rapid diagnostic (LFD) and ELISA for detection of non

Rapid diagnostic (LFD) and ELISA for detection of non-structural protein
antibodies to FMD virus
Foot-and-mouth disease (FMD) is a major livestock disease of transboundary
importance, affecting cloven-hoofed animals including cattle, pigs, goats and sheep. It
is estimated that the annual direct economic loss due to FMD in India is around Rs.
20,000 crores. The Department of Animal Husbandry Dairying and Fisheries,
Government of India has initiated FMD control program (FMD-CP), which aims to
progressively reduce the incidence of the disease through regular mass vaccination. In
situations where a large proportion of the animal population is vaccinated, it is essential
to differentiate infected from vaccinated animals (DIVA), to distinguish between
antibodies produced by vaccination and those developed naturally as a result of viral
infection. Therefore, development of rapid and precise diagnostics facilitating DIVA
would be valuable in the sero-surveillance of FMD when active immunization is
ongoing.
Demonstration of antibodies to non-structural proteins (NSPs) as a result of virus
infection forms the basis of using NSP tests as a DIVA tool. Presence of antibodies
particularly to 3ABC is a reliable indicator of virus activity in vaccinated or naïve
populations. OIE has prescribed ELISA using NSPs such as 3ABC protein, combined
with blot assay as index screening system for demonstrating freedom from infection.
A in-house recombinant ABC based rapid test and ELISA have been developed at
IVRI Bangalore, using 3ABC antigen produced in insect cells (Fig. 1). Indian
Veterinary Research Institute, Bangalore Campus has developed two diagnostic kits
for FMD using insect cell expressed recombinant protein antigen, 3ABC. Both the
tests are rapid, accurate and highly cost effective as compared to similar commercial
kits.
Both tests have been validated by testing different types of serum samples and blood
samples (Rapid test) representing an endemic situation.
Serum
N
P
Serum
Serum samples
P
N
Blood
Serum
samples
LFD strips showing negative (N) and
positive (P) results using serum or blood
samples.
Rapid test:
Rapid tests that don’t need sophisticated
instruments and trained man power are
value additions to the available tools
under
field
conditions.
Pen-side
diagnostics
in
the
form
of
immunochormatographic strip tests or
Lateral Flow Device (LFD) have been
increasingly adapted as diagnostic tools in
human and veterinary medicine. Probably
the most popular and well known
examples of lateral flow tests are home
pregnancy tests. The application of LFDs
has extended to other clinical conditions
including infectious diseases
The lateral flow tests offer greater access, affordability and convenience with wider
acceptability for rapid diagnosis. IVRI has developed a LFD (FMD NSP-Antibody
Rapid Test) for detection of NSP antibodies to FMDV infection. The test, which uses
recombinant protein antigen expressed in insect cells, is validated and its performance
has been comparable with ELISA. The test is rapid, sensitive, specific for diagnosis of
FMD. The biggest advantage with this LFD test is, it does not require cold chain for
transport or storage of the kit, and results can be read with naked eyes without the
need of specialized, costly instruments and trained personnel. The test can be
performed in less than 10 minutes, at the farm level by the veterinarians and farmers.
Field demonstration of the rapid test using
blood samples.
ELISA plate showing test samples along with
positive (PC) and negative controls (NC). BG
indicates background.
Indirect ELISA:
Enzyme labelled antibody based immunoassays provide highly sensitive systems,
allowing detection and quantitation of antigen-specific antibodies in serum or plasma
samples. Baculovirus expressed recombinant 3ABC antigen based ELISA developed
by IVRI has performance highly comparable to similar commercial kits. Diagnostic
sensitivity and specificity for the ELISA were found to be 98 and 97.4, respectively.
The developed ELISA test compared well with two commercial kits showing high
agreement between the assays for a set of known naïve and experimentally FMDV
infected bovine sera. The ELSA kit developed is a highly cost effective substitute for
similar commercial diagnostics, making it very useful in the sero-surveillance of
FMD.
Salient features of the test systems
•
LFD test can be performed by the farmers or field veterinarians. Test does not need
cold chain maintenance thus are handy under field conditions.
•
First such diagnostic developed at IVRI and validated on large scale successfully
•
ELISA is a laboratory test, requiring trained personnel to perform and interpret the
results.
•
Both the tests are highly specific and sensitive and enable differentiation of FMDV
infected from vaccinated population.
•
Assays can be used to detect antibodies in different species of animals that are
susceptible to FMD (cattle, buffaloes, sheep, goats and pigs and other ungulates
including wild species).
•
The assays are highly cost effective compared to similar commercial kits marketed
world wide