Quantitative single serum dilution liquid phase ELISA for the assessment of herd immunity and expectancy of protection against foot-and-mouth disease virus in vaccinated cattle

MATTION, NORA; ROBIOLO, BLANCA; DUFFY, SERGIO; LEON, EMILIO; SEKI, CRISTINA; LA TORRE, JOSE

Viena, Austria

Congreso; FMDWeek2010. New tools and challenges for progressive control.; 2010

European Commission for the Control of FMD.

Introduction: The large number of samples to be tested in foot-and-mouth disease (FMD) epidemiological studies using the competitive liquid phase ELISA (lpELISA) is labor-intensive and expensive.  In the present study, a single serum-dilution liquid phase ELISA (slpELISA) was modified, from the end point dilution lpELISA, and validated for the specific purpose of field studies. Materials and Methods: A quantitative slpELISA was standardized to be used for serological evaluation of herd immunity.  Standard curves were generated by plotting the antibody titers of six control sera determined by end point dilution lpELISA, against the absorbance values for the same control sera at 1:64 dilutions.  Titers of the control sera were selected in order to have at least six points in the linear region of this curve, between 1.40 and 2.40.  The validated standard curve for each FMDV strain, was used to evaluate sample titers by linear regression, by interpolation of their absorbance values at a 1:64 dilution.  Results: A straight line was obtained by linear regression analysis (r>0.90) in the titer range of 1.40 to 2.40.  The reliability of the antibody titers was confirmed by the simultaneous titration of 60 cattle sera by slpELISA and lpELISA, which showed an acceptable correlation (R2 >0.87) for viral strains A24/Cruzeiro, A/Argentina/01, O1/Campos and C3/Indaial.  Titers obtained by both methods were not significantly different (p>0.05). The immunity level of the cattle population in the Argentine province of Buenos Aires was assessed using slpELISA and EPP/PGP correlation tables.  Discussion: The slpELISA could be used successfully to replace the conventional serial dilution ELISA for the assessment of the protection status of cattle in epidemiological studies. It provides an accurate method for monitoring the effectiveness of vaccination campaigns and is also suitable for use for the assessment of seroconversion of naive animals during early stages of infection