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

Abstract

Bovine torovirus (BToV) is recognized as an enteric pathogen of calves, but its etiological role in diarrhea and epidemiological characterization in adult cows remain unclear. In 2007-2008, three outbreaks of epidemic diarrhea occurred in adult cows at three dairy farms in Niigata Prefecture, Japan. BToV was the only enteric pathogen detected in these outbreaks, as determined by electron microscopy, reverse transcription-PCR, bacteria and parasite tests of fecal samples, and antibody tests with paired sera. The epidemiological features of the three outbreaks were similar to those of bovine coronavirus infection, except for the absence of bloody diarrhea, with diarrhea spreading among most adult cows, but not in calves, within several days and diarrhea lasting for 3-5 days with anorexia. Decreased milk production and mild respiratory symptoms were also observed in two of the outbreaks. Nucleotide sequence analysis of the BToV nucleocapsid, spike, and hemagglutinin-esterase (HE) genes revealed a close relatedness among the detected BToV strains from each outbreak and those of Japanese BToV strain Aichi/2004. Furthermore, we isolated a BToV strain, designated Niigata (TC), from a fecal sample using a human rectal tumor cell line. Sequence analysis of this isolate and Aichi/2004 indicated that both strains have truncated HE genes with deletions in the 3' region that occurred through cell culture-adaptation. The short projections that are believed to be formed by the HE protein on virus particles were not observed in these cultured strains by electron microscopy. Taken together, these results suggest that BToV causes epidemic diarrhea in adult cows and should be included in the differential diagnosis of diarrhea in adult cows. In addition, our findings indicate that the HE protein of BToV may not be necessary for viral replication.

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

“…Only one sample among three 0.25-mL fecal suspension samples gave a sufficient number of sequence reads and large contigs, though the number of sequence reads from this sample was lower than that from the viral culture supernatant. Unfortunately, we could not isolate BToV from fecal sample of BToV Kago by using HRT-18-Aich cells, which are useful for BToV isolation (Aita et al, 2012;Ito et al, 2012;Kuwabara et al, 2007), possibly because the samples could not be preserved at −20°C at the veterinary clinic. Although numerous sequence reads originating from bacterial species and hosts might interfere and reduce the number of sequence reads from fecal suspensions, the whole genome sequence of BToV could be obtained from this sample by using our deepsequencing strategy.…”

“…Four BToVs and one PToV were studied. BToV Ishikawa/2010 (BToV Ishi) was isolated using HRT-18-Aich cells (Aita et al, 2012;Kuwabara et al, 2007) from a fecal sample of a cow with diarrhea in Ishikawa Prefecture in 2010 (Ito et al, 2012). BToV Kagoshima/2014 (BToV Kago), BToV Tochigi/2013 (BToV Tochi), and BToV Tokyo/2014 (BToV Tokyo) were detected in the course of metagenomics of fecal samples obtained from 18-, 12-, and 16-day-old calves with diarrhea in Kagoshima, Tochigi, and Tokyo Prefecture in 2014, respectively.…”

“…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).…”

Seroprevalence of porcine torovirus (PToV) in Spanish farms

“…It is important to bear in mind that the closely related BToV is considered a potential important threat for young and neonatal calves [7], on its own or in concurrent infections with other enteric viruses, such as rotavirus and astrovirus, that worsen the disease outcome [6]. In addition, BToV has been recently reported to affect adult dairy cattle production due to diarrhea outbreaks [23]. Moreover, the observed antigenic cross-reactivity between HToV and BToV could suggest the possibility of zoonotic transmission events [7].…”

“…That research made available a source of BToV, which facilitated the development of diagnostic tools to study its epidemiology [7]. The cell culture infectivity of some BToV isolates has been recently reported [8,9]. The presence of toroviral particles in human fecal samples and its association with enteric disease has been shown in several reports [10-12], but the molecular information available about the human torovirus (HToV) is still scarce.…”