DIAGNOSIS OF PERSISTENT APHTHOVIRUS INFECTION AND ITS DIFFERENTIATIONFROM VACCINATION RESPONSE IN CATTLE BY USE OF ENZYME-LINKED IMMUNOELECTROTRANSFER BLOT ANALYSIS WITH BIOENGINEERED NONSTRUCTURAL VIRAL-ANTIGENS

A highly sensitive enzyme-linked immunoelectrotransfer blot (EITB) ass ay, capable of detecting aphthovirus-specific antibodies to replicatin g virus in sera from cattle with persistent infection, was developed. The assay uses a set of purified recombinant DNA-derived nonstructural viral antigens as serologic probes in lieu of the traditionally used virus infection-associated antigen(s) partially purified from baby ham ster kidney-infected cells. Sera from cattle with experimentally induc ed aphthovirus infection were analyzed sequentially by EITB at various postinoculation days, and the results were compared with those obtain ed by currently used techniques. It was established that, in all cases , EITB results remained positive at late stages of infection. At these times, results of virus infection-associated antigen-antibody determi nations were negative by use of the conventional immunodiffusion in ag arose gel test, and virus was recovered only occasionally from esophag eal-pharyngeal fluid. Specificity of the EITB test was indicated by ne gative results for sera from cattle in aphthovirus-free areas, includi ng samples from cattle infected with a variety of bovine viruses. More over, the test eliminated a substantial number of false-positive resul ts (on the basis of the immunodiffusion in agarose gel assay) caused b y reactivity of sera from vaccinated cattle. Use of additional nonstru ctural viral antigens, other than RNA polymerase, is proposed to diffe rentiate between seropositivity resulting from vaccination or infectio n. This procedure may be considered to have potential applications as a sensitive, safe, rapid, and economic field test for specific diagnos is of persistent aphthovirus infection in affected animals.