Detection of cattle exposed to foot‐and‐mouth disease virus by means of an indirect ELISA test using bioengineered nonstructural polyprotein 3ABC

Abstract

An indirect enzyme‐linked immunosorbent assay (I‐ELISA) capable of detecting foot‐and‐mouth disease virus (FMDV)‐specific antibodies in sera from animals with previous viral exposure was developed, as an alternative tool to the enzyme‐linked immunoelectrotransfer blot (EITB) test previously described (Bergmann et al., 1993). Out of the 5 recombinant DNA‐derived FMD nonstructural viral antigens used in the EITB assay, 3ABC was selected, as a serologic probe for the I‐ELISA. High sensitivity for detection of acute as well as of subclinical infection, even at late stages of the persistent status, was indicated by the results for sera from naive animals following experimental infection, or following exposure to the virus under natural conditions. The ability of the test to identify FMDV persistently infected animals subjected to systematic vaccination was also demonstrated. High specificity was revealed by evaluating sera from cattle in FMD‐free regions without vaccination, including samples from cattle infected with a variety of bovine viruses. Analysis of sera from animals in FMD‐free areas under regular vaccination campaigns, including cattle with multiple immunization cycles showed that, ocasionally, antibodies against 3ABC are elicited. The data presented herein indicate that, in agreement with results obtained with the EITB test, the I‐ELISA detected FMDV‐specific antibodies, also at late stages of the persistent infection, maintaining nonspecific reactions at low levels, even in regions under systematic vaccination. Use of the I‐ELISA is suitable as a sensitive, safe, rapid, reproducible 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.