Application of immunoperoxidase techniques to formalin-fixed brain tissue for the diagnosis of rabies in southern Africa.

Two immunoperoxidase techniques, viz. avidin-biotin complex (ABC) and peroxidase-anti-peroxidase (PAP) procedures, were applied to paraffin-wax-embedded brain-tissue sections, from brains which had been fixed in 10% formalin, to demonstrate the presence of rabies-virus antigen by light microscopy. These techniques positively identified both "viverrid" and "canid" rabies-virus antigen in tissues sections of species commonly infected with rabies virus in southern Africa, viz. the domestic dog (Canis familiaris), yellow mongoose (Cynictus penicillata), black-backed jackal (Canis mesomelas), bat-eared fox (Otocyon megalotus), cattle (Bos taurus), sheep (Ovis aries) and humans. With both of these techniques rabies-virus antigen stained as sharply demarcated, brown precipitates within the cytoplasm of neurons. The virtual absence of background staining enabled identification of fine granules of viral antigen, often referred to as "virus dust", within axons, dendrites and cytoplasm of the nerve cell body. Staining with the ABC procedure clearer, more deeply-coloured precipitates than the PAP method.