Genetic and Antigenic Characterization of Newly Isolated Bovine Toroviruses from Japanese Cattle

Abstract

Torovirus, a member of the Coronaviridae family, is a gastrointestinal infectious agent that has been identified in humans, cattle, pigs, and equines. Toroviruses, except equine torovirus, are difficult to propagate in cell culture; indeed, to date, only the Aichi/2004 strain of bovine torovirus (BToV) has been isolated among the human, bovine, and porcine toroviruses. In the present study, four cytopathogenic BToVs were isolated from diarrheal feces of the cattle using the HRT-18 cell line, and their genetic and antigenic properties were compared. The cytopathogenic features of BToV isolates in HRT-18 cells were similar to those of the Aichi/2004 strain. However, none of the isolates showed cytopathogenic effects in the HRT-18 cells of different origin, suggesting that one significant factor contributing to the cytopathogenicity of BToV depends on properties of the HRT-18 cells themselves. All BToVs isolated were able to agglutinate mouse, but not chicken, erythrocytes, while they lacked receptor-destroying enzyme activity. Analysis of the N terminus of the spike gene showed that three isolates, but not the Gifu-2007TI/E strain, were phylogenetically located in cluster 1 and its analogs and revealed high cross-reactivity with each other, as demonstrated by neutralization (NT) and hemagglutination inhibition (HI) assays. The Gifu-2007TI/E strain was classified close to cluster 2 and exhibited relatively low cross-reactivity with these viruses; however, the difference was not sufficient to classify BToVs into serotypes, suggesting that at least two subtypes distinguishable by the structure of the N terminus of the spike gene and that both NT and HI tests may be exist.

Whole genome analysis of Japanese bovine toroviruses reveals natural recombination between porcine and bovine toroviruses

“…3D-G). Ito et al classified Japanese BToVs using 5′ portion of S coding region into three genotypes, Clusters 1-3 (Ito et al, 2007(Ito et al, , 2009(Ito et al, , and 2010. In the phylogenetic tree, the 5′ portion of S coding region of BToVs in this study showed that BToV Ishi and BToV Tochi clustered with Cluster-1 and Cluster-2 strains, respectively, while BToV Kago and BToV Tokyo clustered with Cluster-3 strain, though enough bootstrap support could not be obtained.…”

“…BToV Breda causes enteric disease in gnotobiotic reared calves (Woode et al, 1982). BToVs are found throughout the world including North America (Hoet et al, 2002(Hoet et al, , 2003, Central America (Pérez et al, 1998), Europe (Haschek et al, 2006;Koopmans et al, 1991;Matiz et al, 2002), Asia (Aita et al, 2012;Ito et al, 2010;Park et al, 2008) and South Africa (Penrith and Gerdes, 1992). BToVs have been detected in 2.9-36.4% of fecal samples obtained from cattle with diarrhea (Duckmanton et al, 1998;Hoet et al, 2003;Ito et al, 2007;Kirisawa et al, 2007;Nogueira et al, 2013;Park et al, 2008).…”

Characterization of epidemic diarrhea outbreaks associated with bovine torovirus in adult cows

“…BToVs have been classified into two serotypes on the basis of reactivity in the hemagglutination/HI test [35]. Recently, however, BToVs have been proposed to consist of a single serotype that includes at least two subtypes [12]. In the present study, rabbit antisera to strain Aichi/ 2004 showed no significant differences in virus neutralizing antibody titers between the Aichi/2004 and Nii-gata3(TC) strains, suggesting that these two strains belong to the same serotype.…”

Hemagglutination mediated by the spike protein of cell-adapted bovine torovirus

“…Recently, BToV was isolated from a diarrhea specimen of cattle in Japan, and those isolates were grown in cultured cells, thus making it possible to investigate the ToV replication strategy in more detail [1,12]. The isolate BToV-Aichi exhibited HA activity [7]. Sequence analysis has demonstrated that BToV-Aichi, a tissue-culture-passaged virus with HA activity, lacks a full-length HE gene, and it contains a termination codon midway through the gene ( Fig.…”

“…Erythrocytes for the HA test were collected from 2-monthold Wistar rats (SJD, Shizuoka, Japan) and also from other animals. The antiserum against BToV was prepared in guinea pigs by immunizing them with virions of BToV-Hokkaido [7]. BToV-Hokkaido was revealed to have a truncated HE protein similar to that of BToV-Aichi [7].…”