DETECTION OF CATTLE EXPOSED TO FOOT-AND-MOUTH-DISEASE VIRUS BY MEANS OF AN INDIRECT ELISA TEST USING BIOENGINEERED NONSTRUCTURAL POLYPROTEIN 3ABC

An indirect enzyme-linked immunosorbent assay (I-ELISA) capable of det ecting foot-and-mouth disease virus (FMDV)-specific antibodies in sera from animals with previous viral exposure was developed, as an altern ative tool to the enzyme-linked immunoelectrotransfer blot (EITB) test previously described (Bergmann et al., 1993). Out of the 5 recombinan t DNA-derived FMD nonstructural viral antigens used in the EITB assay, 3ABC was selected as a serologic probe for the I-ELISA. High sensitiv ity for detection of acute as well as of subclinical infection, even a t late stages of the persistent status, was indicated by the results f or sera from naive animals following experimental infection, or follow ing exposure to the virus under natural conditions. The ability of the test to identify FMDV persistently infected animals subjected to syst ematic vaccination was also demonstrated. High specificity was reveale d by evaluating sera from cattle in FMD-free regions without vaccinati on, including samples from cattle infected with a variety of bovine vi ruses. Analysis of sera from animals in FMD-free areas under regular v accination campaigns, including cattle with multiple immunization cycl es showed that, occasionally, antibodies against 3ABC are elicited. Th e data presented herein indicate that, in agreement with results obtai ned with the EITB test, the I-ELISA detected FMDV-specific antibodies, also at late stages of the persistent infection, maintaining nonspeci fic reactions at low levels, even in regions under systematic vaccinat ion. Use of the I-ELISA is suitable as a sensitive, safe, rapid, repro ducible and economic test for the detection of previous virus exposure . A combination of screening by the I-ELISA together with confirmation of suspect serum samples by the more specific EITB assay is proposed for large scale epidemiological surveillance.