in rabies - libdoc.who.int - World Health Organization

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CHAPTER 3 Characteristics and molecular biology of the rabies virus N Tordo ' Introduction Since the early 1980s the availability of molecular biology techniques has made possible a fundamental examination of the causative agents of many d~seases, including rabies The purpose of this chapter IS to review current knowledge of the characteristics of the rabies vlrus to summarize the progress made during the past decade and to atternpl to delineate the main challenges for the future The viruses that cause rabies encephalitis belong to the Lyssawrus genus of the Rhabdoviridae family They were originally classified in four serotypes on the basis of serological and antigenic relationships serotype 1 comprised the classical rabies vlruses notably the ' street (wild) and vaccinal strains serotypes 2 3 and 4 were rabies-related viruses prototyped by Lagos bat Mokola and Duvenhage viruses, respectively The vaccinal strains of serotype l have l~ttle or no protective effect against rabies-related viruses Genetic studies have conf~rmed and extended thls classif~calion (I) Four genotypes corresponding to the four serotypes have been characteri~ed In addition the recently identified European bat lyssaviruses (EBLI and EBL2) have been classified in genotypes 5 and 6 Morphology and structure Morphology The virions or virus particles have a bullet-shaped structure (Fig 3 l), with a diameter of 75 nm and a length of 100-300 nm (2-6) Variations in the length can be observed between rabies strains (e g CVS IS usually longer than PV) or can reflect the presence of defective interfering (D!) particles which occur when the multiplicity of infection is high The D1 particles possess a truncated genorne and are therefore defective in various viral functions and must depend upon infectious virions to comple~nent their deficiency Since their smaller genomes replicate rapidly these particles compete efficiently with normal genomes for encapsidatlon into the virlon The virion can be dvided into two structural unts (Fg 3 2) a central and dense cylinder formed by the helical ribonucleocapsid and a thin surrounding envelope (8 nm wide) covered with spike-like projections which are 10 nm in length and 5 nm apart The helical r~bonucleocapsid is extremely compact as indicated by the huge random ribbon escaping from the flat end of partially degraded virions ' Head, Lyssavlrus Laboratory Pasleur Institute Par~s, France 28
CHARACTERISTICS AND MOLECULAR BIOLOGY OF THE VIRUS Fig. 3.1 Morphology d the rabies A virus (negative-staining electron micaoscopy) A Rabies vinon (genotype I PV stra 11) B Intact Mokola vri~ons (genotype 3 Mok 5 stia~n) C Part~aIly dtsrupied Mokola vi~ions jgenotvpe 3 Mok 5 stratn)
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