Quantitative single dilution liquid phase blocking ELISA for sero-monitoring of foot-and-mouth disease in India.

Three of the seven serotypes of foot-and-mouth disease (FMD) virus are prevailing in India. A massive vaccination campaign is on to control and eradicate the disease from the country. However, FMD vaccines provide short term immunity, hence regular assessment of antibody level in the vaccinated herds is indispensible for the success of the control programme. The antibodies are quantitatively estimated, either by virus neutralization test or by end-point dilution liquid-phase-blocking ELISA (LPBE). Millions of cattle and buffalo in the country are now systematically vaccinated, and thousands of serum samples are routinely screened in the country for estimation of herd immunity against FMDV serotypes O, A and Asia1. Testing such a large number of serum samples within limited a period of time by the conventional end point dilution method of LPBE requires lots of man power, and biological reagents. A more economical high throughput single dilution LPBE (SdLPBE) assay was optimized and validated for quantitative estimation of antibody levels against the three FMD virus serotypes. The assay was thoroughly validated against LPBE method before adopting it for country-wide use. The biological reagents used in the assay were prepared in thermo-stable form to enable transportation to the field level FMD diagnostic laboratories.