THE NONSTRUCTURAL POLYPROTEIN 3ABC OF FOOT-AND-MOUTH-DISEASE VIRUS ASA DIAGNOSTIC ANTIGEN IN ELISA TO DIFFERENTIATE INFECTED FROM VACCINATED CATTLE

A diagnostic assay to differentiate antibodies induced by foot-and-mou th disease virus (FMDV) infection from those induced by vaccination wa s developed. The test is an indirect-trapping ELISA which uses a monoc lonal antibody to trap the non-structural 3ABC-FMDV polypeptide expres sed in E. coli. Experimental and field sera from naive, vaccinated and infected cattle were examined. Using the established threshold of 0.2 0 optical density units, the sensitivity of the assay was 100%, as all the experimental post-infection sera (n degrees = 137) gave values gr eater than this threshold, irrespective of the FMDV serotype used for the infection. In contrast, more than 99% of sera from vaccinated anim als were negative (225 out of 228 prime-vaccinates and 159 out of 159 multi-vaccinates). A high degree of specificity was also confirmed by the finding that 99.5% (442 out of 444) of sera from naive animals gav e negative results. Serum conversion against 3ABC was first detected 8 days post-infection and demonstrable levels of 3ABC specific antibodi es were detectable at least 1 year post-infection. The described 3ABC- ELISA is safe, cheap and also easy to perform in large scale serologic al surveys. The high specificity and sensitivity makes this test an id eal tool for FMD eradication campaigns and control programs.