A New Family of Vertebrate Viruses: <i>Toroviridae</i>

Abstract

The proposed family Toroviridae is characterized by eveloped, peplomer-bearing particles containing an elongated tubular nucleocapsid with helical symmetry. The capsid may bend into an open torus, conferring a biconcave disk or kidney-shaped morphology to the virion (largest diameter 120–140 nm) or the capsid may be straight, resulting in a rod-shaped particle (35 × 170 nm). Morphogenesis is by budding of preformed nucleocapsids through membranes mainly of the Golgi system and of the rough endoplasmic reticulum. Berne virus, which is proposed as the family prototype, contains a single strand of infectious positive-sense RNA, M_r about 6.5 × 10⁶, which is polyadenylated. The RNA is surrounded by the major nucleocapsid phosphoprotein (M_r about 20,000) which, in turn, is enveloped by a membrane containing one major protein (M_r 22,000) and a phosphoprotein (M_r 37,000). The viral peplomers, about 20 nm long, carry determinants for neutralization and hemagglutination; they are formed by a polydisperse N-glycosylated protein (M_r 75,000–100,000). Four major subgenomic polyadenylated RNAs have been identified in infected cells, with M_rs of 3.0,0.71,0.46 and 0.26 × 10⁶. Torovirus replication is inhibited by actinomycin D, alpha-aman-itin and pre-irradiation of the host cell with UV light. All toroviruses identified so far cause enteric infections and are probably transmitted by the fecal-oral route. Serologic relationships between equine, bovine and human toroviruses have been demonstrated.

Toroviruses: replication, evolution and comparison with other members of the coronavirus-like superfamily

“…Snijder and M. C. Horzinek (c) and the physicochemical properties of BEV (Weiss & Horzinek, 1986a) led to the proposal of a new family of enveloped animal viruses, the Toroviridae Horzinek et al, 1987;; BEV, the only torovirus so far which can be grown in cultured cells, was identified as the prototype.…”

“…Based on their morphological and physicochemical characteristics, the Toroviridae were initially proposed to constitute a new family of enveloped RNA viruses Horzinek et al, 1987). However, recent analysis of the genetic information and replication strategy of the prototype Berne virus (BEV) (Snijder et al, 1988(Snijder et al, , 1990a has revealed that toroviruses are not unique: they are clearly related to the Coronaviridae and, more distantly, to the arteriviruses (den Boon et al, 1991 b).…”

Characterization of Berne Virus Genomic and Messenger RNAs

“…Berne virus (BEV) of horses is a representative of a recently defined group of vertebrate RNA viruses, for which the family status and the name Toroviridae have been proposed Horzinek et al, 1987); antigenically related toroviruses have been demonstrated in cattle (Woode et al, 1985) and humans (Beards et al, 1984). The present state of knowledge regarding the toroviruses has been reviewed recently (Weiss & Horzinek, 1987;Horzinek et al, 1987).…”

“…The present state of knowledge regarding the toroviruses has been reviewed recently (Weiss & Horzinek, 1987;Horzinek et al, 1987). The equine isolate BEV is the best studied member of the proposed family, since it is the only torovirus so far that can be propagated in cultured cells.…”

Characterization of defective interfering RNAs of Berne virus

“…Berne virus (BEV) is the type species of a group of enveloped positive-strand RNA viruses, the toroviruses (Horzinek & Weiss, 1984;Horzinek et al, 1987), which has recently been recognized (by the International Committee on Taxonomy of Viruses) as 'a new genus with possible affinities to the coronavirus family'. During the past 4 years, analysis of the BEV genome structure and replication strategy has revealed that toroviruses are evolutionarily related to coronaviruses.…”