Safe and easy monitoring of anti-rabies antibody in dogs using his-tagged recombinant N-protein.

The virus neutralization (VN) test is a reliable indicator of adequate vaccination in animals. However, the VN test is tedious and complicated to perform. Enzyme-linked immunosorbent assay (ELISA), though rapid and simple compared to the VN test, is complicated and hazardous during preparation of the viral antigen. In an effort to overcome the disadvantage of ELISA, the recombinant His-tagged nucleoprotein (His-rNP) expressed in Escherichia coli was used as a safe antigen for ELISA (i.e., live virus was not used). Anti-rabies antibody levels were determined by fluorescent ELISA (FELISA) using His-rNP as an antigen. The presence of anti-rabies VN antibody was determined by the rapid fluorescent focus inhibition test (RFFIT). The VN titers by RFFIT were found to correlate well with the FITC-signal determined by the FELISA (r = 0.616). The sensitivity and specificity of the FELISA were 91.7 and 100%, respectively. This study showed that the His-rNP could be useful as an antigen of ELISA to test for anti-rabies antibody in vaccinated dogs. Several studies in Japan have investigated the antibody level in the sera of vaccinated dogs. A safe and convenient test using His-rNP would contribute to our understanding of the status of herd immunity among not only domestic dogs but also stray dogs in Japan.