Epidemiological analysis of bovine torovirus in Japan

Prevalence of bovine astroviruses and their genotypes in sampled Chinese calves with and without diarrhoea

Bovine astrovirus (BoAstV) belongs to genus Mamastravirus (MAstV). It can be detected in the faeces of both diarrhoeal and healthy calves. However, its prevalence, genetic diversity, and association with cattle diarrhoea are poorly understood. In this study, faecal samples of 87 diarrhoeal and 77 asymptomatic calves from 20 farms in 12 provinces were collected, and BoAstV was detected with reverse transcription-polymerase chain reaction (RT-PCR). The overall prevalence rate of this virus in diarrhoeal and asymptomatic calves was 55.17 % (95 % CI: 44.13, 65.85 %) and 36.36 % (95 % CI: 25.70, 48.12 %), respectively, indicating a correlation between BoAstV infection and calf diarrhoea (OR=2.15, P=0.024). BoAstV existed mainly in the form of co-infection (85.53 %) with one to five of nine viruses, and there was a strong positive correlation between BoAstV co-infection and calf diarrhoea (OR=2.83, P=0.004). Binary logistic regression analysis confirmed this correlation between BoAstV co-infection and calf diarrhoea (OR=2.41, P=0.038). The co-infection of BoAstV and bovine rotavirus (BRV) with or without other viruses accounted for 70.77 % of all the co-infection cases. The diarrhoea risk for the calves co-infected with BoAstV and BRV was 8.14-fold higher than that for the calves co-infected with BoAstV and other viruses (OR=8.14, P=0.001). Further, the co-infection of BoAstV/BRV/bovine kobuvirus (BKoV) might increase the risk of calf diarrhoea by 14.82-fold, compared with that of BoAstV and other viruses (OR=14.82, P <0.001). Then, nearly complete genomic sequences of nine BoAstV strains were assembled by using next-generation sequencing (NGS) method. Sequence alignment against known astrovirus (AstV) strains at the levels of both amino acids and nucleotides showed a high genetic diversity. Four genotypes were identified, including two known genotypes MAstV-28 (n=3) and MAstV-33 (n=2) and two novel genotypes designated tentatively as MAstV-34 (n=1) and MAstV-35 (n=3). In addition, seven out of nine BoAstV strains showed possible inter-genotype recombination and cross-species recombination. Therefore, our results increase the knowledge about the prevalence and the genetic evolution of BoAstV and provide evidence for the association between BoAstV infection and calf diarrhoea.

Recent Progress in Torovirus Molecular Biology

Torovirus (ToV) has recently been classified into the new family Tobaniviridae, although it belonged to the Coronavirus (CoV) family historically. ToVs are associated with enteric diseases in animals and humans. In contrast to CoVs, which are recognised as pathogens of veterinary and medical importance, little attention has been paid to ToVs because their infections are usually asymptomatic or not severe; for a long time, only one equine ToV could be propagated in cultured cells. However, bovine ToVs, which predominantly cause diarrhoea in calves, have been detected worldwide, leading to economic losses. Porcine ToVs have also spread globally; although they have not caused serious economic losses, coinfections with other pathogens can exacerbate their symptoms. In addition, frequent inter- or intra-recombination among ToVs can increase pathogenesis or unpredicted host adaptation. These findings have highlighted the importance of ToVs as pathogens and the need for basic ToV research. Here, we review recent progress in the study of ToV molecular biology including reverse genetics, focusing on the similarities and differences between ToVs and CoVs.

First report and genetic characterization of bovine torovirus in diarrhoeic calves in China

Background

Coronaviruses are notorious pathogens that cause diarrheic and respiratory diseases in humans and animals. Although the epidemiology and pathogenicity of coronaviruses have gained substantial attention, little is known about bovine coronavirus in cattle, which possesses a close relationship with human coronavirus. Bovine torovirus (BToV) is a newly identified relevant pathogen associated with cattle diarrhoea and respiratory diseases, and its epidemiology in the Chinese cattle industry remains unknown.

Results

In this study, a total of 461 diarrhoeic faecal samples were collected from 38 different farms in three intensive cattle farming regions and analysed. Our results demonstrated that BToV is present in China, with a low prevalence rate of 1.74% (8/461). The full-length spike genes were further cloned from eight clinical samples (five farms in Henan Province). Phylogenetic analysis showed that two different subclades of BToV strains are circulating in China. Meanwhile, the three BToV strains identified from dairy calves, 18,307, 2YY and 5YY, all contained the amino acid variants R614Q, I801T, N841S and Q885E.

Conclusions

This is the first report to confirm the presence of BToV in beef and dairy calves in China with diarrhea, which extend our understanding of the epidemiology of BToVs worldwide.

Molecular detection of bovine coronavirus in a diarrhea outbreak in pasture-feeding Nellore steers in southern Brazil

Worldwide diarrhea outbreaks in cattle herds are more frequently detected in calves being that diarrhea outbreaks in adult cattle are not common. Winter dysentery (WD) is a bovine coronavirus (BCoV) enteric infection that is more reported in Northern hemisphere. Seasonal outbreaks of WD in adult cattle occur mainly in dairy cows. WD has not been described in beef cattle herds of tropical countries. This study describes the molecular detection of BCoV in a diarrhea outbreak in beef cattle steers (Nellore) raised on pasture in Parana, southern Brazil. During the outbreak, the farm had about 600 fattening steers. Watery and bloody diarrhea unresponsive to systemic broad-spectrum antibiotic therapy reveals a morbidity rate of approximately 15 %. The BCoV N gene was identified in 42.9 % (6/14) of the diarrheic fecal samples evaluated by semi-nested polymerase chain reaction (SN-PCR) technique. Other enteric microorganisms occasionally identified in adult cattle and evaluated in this study such as bovine groups A, B, and C rotavirus, bovine viral diarrhea virus, bovine torovirus, aichivirus B, and Eimeria sp. were not identified in the fecal samples. To the best knowledge of the authors, this is the first description of the BCoV diagnosis in fecal samples collected in a diarrhea outbreak in adult beef cattle grazing in the grass in a tropical country.

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

Bovine toroviruses (BToVs), belong to the subfamily Toroviridae within the family Coronaviridae, and are pathogens, causing enteric disease in cattle. In Japan, BToVs are distributed throughout the country and cause gastrointestinal infection of calves and cows. In the present study, complete genome sequences of two Japanese BToVs and partial genome sequences of two Japanese BToVs and one porcine torovirus (PToV) from distant regions in Japan were determined and genetic analyses were performed. Pairwise nucleotide comparison and phylogenetic analyses revealed that Japanese BToVs shared high identity with each other and showed high similarities with BToV Breda1 strain in S, M, and HE coding regions. Japanese BToVs showed high similarities with porcine toroviruses in ORF1a, ORF1b, and N coding regions and the 5′ and 3′ untranslated regions, suggestive of a natural recombination event. Recombination analyses mapped the putative recombinant breakpoints to the 3′ ends of the ORF1b and HE regions. These findings suggest that the interspecies recombinant nature of Japanese BToVs resulted in a closer relationship between BToV Breda1 and PToVs.

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Recombination events between porcine and bovine torovirus were identified.

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Recombinant breakpoints were mapped at ORF1b and HE coding regions.

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These recombinant viruses are prevalent throughout Japan.

Detection and molecular characterisation of bovine corona and toroviruses from Croatian cattle

BACKGROUND

Bovine coronavirus (BCoV) together with bovine torovirus (BToV), both members of the Coronaviridae family, order Nidovirales are the most common viral enteric pathogens. Although studied separately, their joint occurrence and the molecular diversity in cattle in Croatia have not been investigated.

METHODS

A survey is carried out on 101 fecal samples from diarrheic young and adult cattle during the 3-year period from i) one large dairy herd, ii) four small herds and iii) three nasal and paired fecal samples from calves with symptoms of respiratory disease. Samples were submitted to RT-PCR and sequencing for BCoV Nucleocapsid gene, BCoV Spike gene and BToV Spike gene.

RESULTS

BCoV was detected in 78.8 % of fecal samples from symptomatic cattle and three nasal and paired fecal samples from calves with respiratory symptoms. BToV was detected in 43.2 % of fecal samples from symptomatic cattle and a fecal sample from calves with respiratory symptoms. Molecular characterisation of those viruses revealed some nucleotide and aminoacid differences in relation to reference strains.

CONCLUSIONS

BToV should be regarded as a relevant pathogen for cattle that plays a synergistic role in mixed enteric infections.

Detection of bovine torovirus in fecal specimens from calves with diarrhea in Turkey

Bovine torovirus (BToV), a member of the family Coronaviridae, is an established gastrointestinal infectious agent in cattle. In this study, we performed a survey to detect BToV in Turkey between 2009 and 2011 using 235 fecal samples from neonatal calves with diarrhea that were analyzed by the nested reverse transcription (RT) PCR method using primers located in the consensus sequences of the BToV membrane (M) gene. The BToV M gene was detected in 4.7 % (11/235) of the samples using the nested RT-PCR method. The nucleotide sequences of partial M fragments from the BToV isolates, including the newly identified Turkish isolates, showed more than 96 % identity. The result indicates that BToV is one of the pathogens that contribute to neonatal calf diarrhea cases in Turkey.

First detection and molecular diversity of Brazilian bovine torovirus (BToV) strains from young and adult cattle

Bovine torovirus (BToV) is an established enteric pathogen of cattle, but its occurrence in Brazilian cattle had not been reported until now. This article describes a survey on BToV in Brazil carried out on 80 fecal samples from diarrheic young and adult cattle, using a nested-RT-PCR targeting the nucleocapsid (N) gene. BToV was detected in 6.25% (5/80) of stool samples from three different geographic regions. Sequences analysis showed that Brazilian BToVs have a high degree of identity with European and Japanese BToVs and a lower degree of identity with North American Breda 1 strain. These results show that, albeit its low frequency and the scarce number of research on the field, BToV is still present amongst cattle populations.

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

Bovine torovirus (BToV)-Aichi, recently isolated in cultured cells, showed hemagglutination (HA) activity, although the virus has a truncated hemagglutinin-esterase (HE) protein, judging from its gene structure, indicating the existence of another viral protein with HA activity. We examined whether the spike (S) protein possesses HA activity. A BToV antiserum used in this study, reactive to S but not to HE, inhibited HA activity. Furthermore, cells infected with BToV and those expressing S showed hemadsorption (HAD) activity, which was inhibited by the anti-BToV serum; however, HAD activity by expressed HE was not blocked. These data indicate that the S protein of BToV-Aichi is responsible for its HA activity.

Development and application of one-step multiplex reverse transcription PCR for simultaneous detection of five diarrheal viruses in adult cattle

A one-step multiplex reverse transcription (RT)-PCR method was developed for the simultaneous detection of five viruses causing diarrhea in adult cattle: bovine group A rotavirus (GAR), bovine group B rotavirus (GBR), bovine group C rotavirus (GCR), bovine coronavirus (BCV), and bovine torovirus (BToV). The detection limit of the one-step multiplex RT-PCR for GAR, GCR, BCV, and BToV was 10², 10⁰, 10¹, and 10² TCID₅₀/ml, respectively, and that for GBR was 10⁶ copies/ml. The one-step multiplex RT-PCR with newly designed primers to detect GAR had higher sensitivity than a single RT-PCR with conventional primers, with no false-positive reactions observed for ten other kinds of bovine RNA viruses To assess its field applicability, 59 of 60 fecal samples containing one of these five viruses from all 25 epidemic diarrhea outbreaks in adult cattle were positive in the one-step multiplex RT-PCR assay. Furthermore, using four additional fecal samples containing two viruses (GBR and BCV or BToV), two amplified products of the expected sizes were obtained simultaneously. In contrast, all 80 fecal samples lacking the five target viruses from normal adult cattle were negative in the multiplex assay. Taken together, our results indicate that the one-step multiplex RT-PCR developed here for the detection of GAR, GBR, GCR, BCV, and BToV can be expected to be a useful tool for the rapid and cost-effective diagnosis and surveillance of viral diarrhea in adult cattle.

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

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.

Synthesis and inhibitory activity of sialic acid derivatives targeted at viral sialate-O-acetylesterases

A series of sialosides modified at the 4- and 9-hydroxy group were synthesised and tested for inhibition of the viral haemagglutinin-esterase activity from various Orthomyxoviruses and Coronaviruses. While no inhibition of the sialate-4-O-acetylesterases from mouse hepatitis virus strain S or sialodacryoadenitis virus was found, a 9-O-methyl derivative displayed inhibitory activity against recombinant sialate-9-O-acetylesterase from influenza C virus.

Development of universal SYBR Green real-time RT-PCR for the rapid detection and quantitation of bovine and porcine toroviruses

Toroviruses (ToVs) are a group of emerging viruses that cause gastroenteritis in domestic animals and humans. Currently, methods such as real-time reverse transcription-polymerase chain reaction (real-time RT-PCR) have not yet been developed for the rapid detection and quantitation of bovine (BToV) and porcine (PToV) toroviruses. Using BToV and PToV RNA standards generated by in vitro transcription, the detection limit of the SYBR Green real-time RT-PCR assay was 2.54 x 10(2) BToV and 2.17 x 10(3) PToV copies/reaction (correlation coefficiency=0.99 and 0.97, respectively), whereas those of RT-PCR and nested PCR were 2.54 x 10(5) and 2.54 x 10(4) (BToV) and 2.17 x 10(7) and 2.17 x 10(5) (PToV) cRNA viral copies/reaction, respectively. Archived diarrhea specimens of calves (n=121) and piglets (n=86) were subjected to RT-PCR, nested PCR and SYBR Green real-time RT-PCR. By conventional RT-PCR, 1 (0.8%) bovine and 7 (8.1%) porcine samples tested positive to BToV and PToV, respectively. With nested PCR, 13 (10.7%) bovine and 17 (19.8%) porcine samples tested positive. SYBR Green real-time RT-PCR assay detected BToV and PToV in 22 of 121 (18.2%) bovine and 31 of 86 (36.0%) porcine samples. These results indicate that SYBR Green real-time RT-PCR (P<0.05) is a more sensitive assay, which can be reproduced as a reliable, sensitive, and rapid tool for the detection and quantitation of toroviruses.

Longitudinal serological and virological study on porcine torovirus (PToV) in piglets from Spanish farms

A study was performed to evaluate porcine torovirus (PToV) seroprevalence and infection in three multi-site farms from the North-eastern region of Spain. Serum samples from 120 piglets and faecal samples from 36 piglets were longitudinally collected at 1, 3, 7, 11 and 15 weeks of age. Serum samples from their dams (n = 30) were also taken 1-week post-farrowing. PToV antibodies in serum were monitored by ELISA, while viral infection was assessed by real-time RT-PCR in faeces. A high seroprevalence (about 100%) was observed in animals older than 11 weeks and in adult sows. Moreover, all 1-week-old animals were seropositive, indicating maternal antibody transference through colostrum. The antibody titers declined to close to or below the ELISA cut-off value by the age of weaning (3 weeks of age). Development of a significant antibody response to PToV occurred before 7 weeks of age in about 50% of piglets, and the remaining animals developed the response by weeks 11 or 15. These results indicate that PToV infection occurred soon after weaning. Although the prevalence of infection in suckling piglets varied among the studied farms, PToV prevalences in 7 and 11-week-old pigs were between 50–67% and 58–75%, respectively, in all farms. Sequencing results indicated that more than one PToV strains were circulating in the studied farms. Present data suggest that PToV was endemic on the studied farms, and provide new insights on the epidemiology of PToV.

Genetic and antigenic characterization of newly isolated bovine toroviruses from Japanese cattle

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.

Detection and molecular characterization of porcine toroviruses in Korea

This study examined the prevalence and genetic diversity of the porcine torovirus (PToV) in Korea. Of 295 samples, 19 (6.4%) samples tested positive for PToVs by RT-PCR. A low nucleotide sequence identity of the partial S gene was detected among the Korean PToVs (73.5%) and between the Korean and European PToVs (74.0%). Phylogenetic analysis of the spike and nucleocapsid genes showed that the Korean PToVs form distinct branches with clusters corresponding to the farm of origin, which were separate from the other known foreign PToVs. These findings suggest that genetically diverse Korean PToV strains cause sporadic infections in Korea.

Detection of porcine torovirus by real time RT-PCR in piglets from a Spanish farm

Toroviruses are enteric viruses belonging to the Nidovirales order that infect different animal species and humans. The lack of "in vitro" culture systems for toroviruses, except for the prototype Berne virus or BEV, isolated originally from an infected horse, has hampered their study and the development of diagnostic assays. This report describes a real time RT-PCR method to detect porcine torovirus (PToV) RNA in clinical fecal samples using primers corresponding to the gene coding for the nucleocapsid protein which are conserved in all PToV strains known to date. This method can be used to determine viral loads allowing quantitation within a range between 10(1) and 10(8) genomic units per reaction tube. The assay was evaluated with 48 rectal swabs from piglets from a Spanish farm. Nineteen out of 48 animals were shedding virus at the time of sample collection, indicating a high incidence of PToV infection in this farm. This is the first report showing the presence of PToV in Spain. The real time RT-PCR assay described in this report provides a rapid, highly sensitive, specific and reliable detection and quantitation method enabling future PToV epidemiological studies.

Molecular characterization of a new PToV strain. Evolutionary implications

Toroviruses are emergent viruses, belonging to the Nidovirales order, that remain mostly ignored, despite they are able to infect different species of domestic animals and humans, causing enteric diseases and diarrhea. Thus far, only five variants of porcine torovirus (PToV) have been identified. In this report we describe the identification and partial characterization of a new strain of porcine torovirus (PToV-BRES) that was detected by RT-PCR in a swine faecal specimen from a farm in Brescia (Italy). The complete genes coding for the nucleocapsid (N), hemagglutinin-esterase (HE) and membrane (M) proteins were amplified, and sequence analysis showed that PToV-BRES is a new PToV strain that, based on the HE gene sequence, is phylogenetically related to P4 strain, that was up to now the only member of a distinct PToV lineage. The nucleocapsid protein from PToV-BRES was expressed in insect cells as a his-tagged protein, purified by affinity chromatography and used to develop an ELISA method to detect antibodies against PToV. This assay was evaluated using a serum collection including 45 samples from three commercial farms from Spain. High antibody prevalence against PToV was observed in the three farms, both in adult animals and in piglets, which could suggest that PToV might be endemic in Spanish porcine population. The ELISA method developed in this work could be useful in future epidemiological surveys about toroviruses.

Detection and characterization of bovine torovirus from the respiratory tract in Japanese cattle

Bovine torovirus (BToV), a member of the Coronaviridae family, is a causative agent of diarrhea in cattle, but it may also possess tropism for the respiratory tract. However, no surveys concerning with the relation between respiratory symptoms and the detection of BToV have been conducted in wide range. Among 311 nasal samples, BToV gene products were detected in seven samples (rBToV-1 to -7) derived only from calves with respiratory symptoms, suggesting that BToV may be a predisposing factor and/or causative agent for bovine respiratory disease. Regarding the degree of similarity between the spike and hemagglutinin-esterase coding regions, the rBToVs showed over 90.8% similarity with one another and 73.5–99.0% similarity with fecal tract-derived BToVs. rBToV-1, -2, and -3 were identical despite their being collected during different seasons; in comparison, rBToV-4 and -5 were distinct despite the fact that they were collected from the same herd, suggesting the existence of diversity among domestic rBToVs. One animal with a BToV-positive nasal sample also shed the virus in its feces, suggesting dual tropisms for BToV.

Molecular epidemiology of bovine toroviruses circulating in South Korea

The prevalence of the bovine torovirus (BToV) and its genetic characterization have been reported in North America, Europe and Japan. Therefore, this study examined the prevalence and genetic diversity of the BToV in a total of 645 diarrheic fecal samples from 629 Korean native beef calf herds using RT-PCR and nested PCR with the primer pairs specific to a part of the BToV membrane (M) gene. Overall, 19 (2.9%) out of 645 diarrheic samples from 19 herds (6.9%) tested positive for BToVs by either RT-PCR or nested PCR. A comparison of the nucleotide (nt) and amino acid (aa) sequences of a part of the BToV M gene (409bp) among the BToVs showed the Korean BToVs to have comparatively higher sequence homology to the Japanese and Dutch BToVs than to the American and Italian BToVs. Generally, the Korean BToV strains clustered with the Japanese and Dutch BToV strains. However, the American and Italian BToV strains clustered on a separate major branch, suggesting that these are more distantly related to other known BToV strains. These results suggest that the BToV infections are sporadic in diarrheic calves in South Korea, and the Korean BToV strains are more closely related to the Japanese and Dutch BToVs than to the American and Italian BToVs.