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Chapter 91 : Rabies Virus
The etiologic agents responsible for the acute, progressive viral encephalomyelitis known as rabies belong to the genus Lyssavirus. The virions are rod shaped, approximately 180 by 75 nm, consisting of five structural proteins: the glycoprotein (G), matrix protein (M), nucleoprotein (N), phosphoprotein (P), and large polymerase (L). Human rabies cases due to nonbite exposures are extremely rare. Nonbite exposures include contamination of scratches, open wounds, and mucous membranes with a source of rabies virus, such as infected saliva or central nervous system (CNS) tissues from a rabid animal. Four antemortem clinical samples are required for diagnosing rabies: saliva for nested reverse transcription-polymerase chain reaction (RT-PCR) and/or virus isolation, nuchal skin biopsy for antigen detection and nested RT-PCR, and serum and cerebrospinal fluid (CSF) for immunoglobulin M (IgM) and IgG antibody determination. The standard test for rabies virus antigen detection in CNS tissues is the direct fluorescent-antibody (DFA) test. The direct rapid immunohistochemistry (IHC) test (DRIT) is an alternate procedure for rabies virus antigen detection. An immunohistochemistry test for rabies virus antigen detection is an alternative protocol for formalin- fixed tissue samples which have been processed, embedded in paraffin, and sectioned. Isolation methods are useful in detecting infectious virus in samples and may be applied as an alternate confirmatory test to the standard DFA. Cell cultures may be useful in the propagation, amplification, and quantification of virus and antibodies, to produce vaccines, to determine the safety of vaccine lots, and to study the pathogenesis of rabies virus in particular cells.