Identification of foot-and-mouth disease virus-free regions by use of a standardized enzyme-linked immunoelectrotransfer blot assay

Abstract

Objective - To assess the potential of a highly sensitive enzyme-linked immunoelectrotransfer blot (EITB) assay to monitor persistent foot-and-mouth disease (FMD) viral activity in a livestock population. Design - Cattle sera were obtained in Uruguay in 1992, 2 years after the last outbreaks of FMD. Prevalence of antibodies, as assessed by the EITB assay and by the conventional immunodiffusion in agarose gel method (virus infection-associated antigen [VIAA] test), was correlated with occurrence of FMD. Sample Population - A total of 2,194 serum samples were acquired from animals at different farms and were separated according to age: animals < and > 2 years old. Procedure - Specific antibodies to replicating virus were detected by use of the EITB assay that utilizes a set of 5 bioengineered nonstructural antigens as serologic probes. Results - EITB-positive reaction was restricted to sera from cattle in areas with the last outbreaks of FMD during 1989-1990, and to animals > 2 years old. All cattle sera from regions that were free of clinical FMD since (or prior to) 1989 were EITB negative. In contrast, use of the VIAA test yielded a rather homogeneous distribution of positive results when regions without FMD during the last 4 years preceding sample collection were compared with those affected during 1989-1990. VIAA test-positive reaction was also found in sera from animals born after the last FMD outbreak. Conclusions - The EITB assay proved to be a sensitive, specific, safe, rapid, and economic tool for monitoring the progress of FMD eradication programs, mainly because it eliminated false-positive results from the VIAA test.