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

Abstract

PROCEEDINGSdeveloped, particularly for detecting the circulation of FMD virus in a subclinical form in FMD-vaccinated populations.When adapted for use in sheep, the 3ABC MAt-ELISA showed similar specificity, giving negative results with sera from vaccinated animals and positive in experimentally infected sheep that developed antibodies to FMDV structural proteins. In field conditions, the test was able to detect silent infections in asymptomatic sheep. However, there was more variation in antibody levels in naturally exposed animals than in experimental animals and not all sheep suspected to have been exposed to infection scored positive to 3ABC, (in spite of the detection of antibodies to sructural proteins) The failure to detect 3ABC induced antibodies in such animals could reflect a possible, individual immuno-tolerance to 3ABC, a poor sensitivity of the test, or the occurrence of a previous, unknown vaccination. Alternatively, the delayed onset and the shorter half-life of anti-3ABC antibodies with respect to antibodies against structural proteins should be considered.In conclusion, the demonstration of antibodies to 3ABC is conclusive evidence of FMD infection. Following extensive validation, the 3ABC MAt-ELISA is indicated to detect viral circulation in FMD-vaccinated populations, representing a valuable diagnostic tool for FMD eradication campaigns and control programs. For the application on a single animal further research is required, mainly in two directions: i) the correlation between 3ABC antibodies and the carrier status, ii) the immune response to both structural and non-structural FMDV proteins in sheep and other species following infection. ACKNOWLEDGEMENTS

Comparison of Two 3ABC Enzyme-Linked Immunosorbent Assays for Diagnosis of Multiple-Serotype Foot-and-Mouth Disease in a Cattle Population in an Area of Endemicity

“…No previous publications mention this kit, although several studies used a similar format with an E. coli-expressed protein. The parameter estimates were high, with an Se of 100% and an Sp of 99% in cattle 20 days postinfection (31) and an Se of 92% and an Sp of 90% in sheep (7). However, these studies were based on small, experimentally infected groups rather than naturally infected populations.…”

Pan-Serotype Diagnostic for Foot-and-Mouth Disease Using the Consensus Antigen of Nonstructural Protein 3B

“…Recombinant c3B was generated using a synthetic codon-optimized gene in BL21 E. coli. Previous studies that used E. coliexpressed proteins to develop FMDV diagnostic tests required the addition of E. coli lysates to sample serum diluents, to preabsorb nonspecific background reactivity (39,52). It has been suggested that this background reactivity may be due in part to inclusion of the N-terminal 3A sequence, which shares sequence homology with a transposase IS4 family protein from E. coli (53).…”

“…The reference DIVA test adopted by the OIE for FMDV is an ELISA that detects antibodies against the NSP 3ABC (NCPanaftosa screening test) complemented by an enzyme-linked immunoelectrotransfer blot assay (12,38). A problem associated with the use of 3ABC is the presence of vaccine-associated 3A protein, which may complicate DIVA testing due to the presence of 3A-specific antibodies in sera from some vaccinated cattle (15,39,40). Furthermore, due to its expression as insoluble inclusion bodies in E. coli and the presence of the autocatalytic 3C protein segment, recombinant 3ABC is difficult to produce (28, 41-43; our unpublished observations).…”

Foot-and-Mouth Disease, an Economically Important Disease of Animals

“…The magnitude of the antibody response against NSPs is variable; 3A, 3B, 3D and 3 ABC could be detected in cattle as early as 7-10 days post infection (Bergmann et al, 1993;Sorensen et al, 1998) and up to 560-742 days post infection (Silberstein et al, 1997;Malirat et al, 1998). However, in sheep, these develop later; against 3ABC at 14 days and against 3D after 22 days post infection.…”