Evaluation of an indirect rapid immunohistochemistry test for the differentiation of rabies virus variants.

Cost effective diagnostic tests are needed in rabies virus (RABV) enzootic areas to study the prevalence, distribution, and transmission of rabies virus among reservoir hosts. To reduce the associated costs of acquiring and maintaining specialized laboratory equipment, an indirect rapid immunohistochemistry test (IRIT), for the detection and differentiation of RABV variants, was evaluated by traditional light microscopy. The IRIT utilizes fresh frozen brain touch impressions or cell culture monolayers fixed in buffered formalin, a panel of murine anti-nucleoprotein monoclonal antibodies (mAb-N) and commercially available biotin-labeled goat anti-mouse antibody. In this study, 96 RABV isolates, representing 20 RABV variants previously determined by antigenic typing using a panel of mAb-N and the indirect fluorescent antibody test (IFA), and genetic sequence analysis were characterized by IRIT and the results compared. The IRIT results revealed distinct reactivity patterns associated with current and historical RABV reservoir hosts similar to IFA test and genetic sequence analysis. Evaluation of suspected RABV samples through IRIT does not require specialized equipment and is possible to perform in a field setting. Additionally, commercially available labeled secondary antibodies permit the use of a standard panel of unlabeled primary mAbs, without the need for fluorescence microscopy, and should augment existing attempts at antigenic characterization during canine rabies elimination campaigns in developed and developing countries. These results are useful in studying the epizootiology of rabies and inferring the source of infection when unknown.