Identification and characterization of a porcine torovirus

A porcine torovirus (PoTV) was identified and characterized; it is a novel member of the genus Torovirus (family Coronaviridae, order Nidovirales), closely related to but clearly distinct from the already recognized equine torovirus (ETV) and bovine torovirus (BoTV) representatives. Immunoelectron microscopy of feces from piglets revealed elongated, 120- by 55-nm particles which were recognized by a torovirus-specific antiserum. Amplification by reverse transcriptase (RT) PCR with primers designed to detect conserved regions (on the basis of the genomes of BoTV strain Breda and ETV strain Berne) resulted in the identification of the 489-bp nucleocapsid gene, encoding a 18.7-kDa protein. The sequence identity in this region between PoTV and both ETV and BoTV was only about 68%, whereas the latter two show 81% identity. Neutralizing antibodies directed against ETV were found in sera of adult and young pigs. In all 10 herds sampled, seropositive animals were present, and 81% of randomly selected adult sows possessed antibodies. A longitudinal study with RT PCR showed that piglets shed virus in the feces for 1 or more days, starting 4 to 14 days after weaning.

Phylogenetic and evolutionary relationships among torovirus field variants: evidence for multiple intertypic recombination events

Toroviruses (family Coronaviridae, order Nidovirales) are enveloped, positive-stranded RNA viruses that have been implicated in enteric disease in cattle and possibly in humans. Despite their potential veterinary and clinical relevance, little is known about torovirus epidemiology and molecular genetics. Here, we present the first study into the diversity among toroviruses currently present in European swine and cattle herds. Comparative sequence analysis was performed focusing on the genes for the structural proteins S, M, HE, and N, with fecal specimens serving as sources of viral RNA. Sequence data published for animal and human torovirus variants were included. Four genotypes, displaying 30 to 40% divergence, were readily distinguished, exemplified by bovine torovirus (BToV) Breda, porcine torovirus (PToV) Markelo, equine torovirus Berne, and the putative human torovirus. The ungulate toroviruses apparently display host species preference. In phylogenetic analyses, all PToV variants clustered, while the recent European BToVs mostly resembled the New World BToV variant Breda, identified 19 years ago. However, we found ample evidence for recurring intertypic recombination. All newly characterized BToV variants seem to have arisen from a genetic exchange, during which the 3' end of the HE gene, the N gene, and the 3' nontranslated region of a Breda virus-like parent had been swapped for those of PToV. Moreover, some PToV and BToV variants carried chimeric HE genes, which apparently resulted from recombination events involving hitherto unknown toroviruses. From these observations, the existence of two additional torovirus genotypes can be inferred. Toroviruses may be even more promiscuous than their closest relatives, the coronaviruses and arteriviruses.

Detection of bovine torovirus in fecal specimens of calves with diarrhea from Ontario farms

Breda virus (BRV), a member of the genus Torovirus, is an established etiological agent of disease in cattle. BRV isolates have been detected in the stools of neonatal calves with diarrhea in both Iowa and Ohio and in several areas of Europe. However, this virus has been reported only once in Canada. Therefore, a study was performed to determine the extent to which bovine torovirus is present in calves with diarrhea from farms in southern Ontario. A total of 118 fecal samples from symptomatic calves and 43 control specimens from asymptomatic calves were examined by electron microscopy (EM) and reverse transcription-PCR (RT-PCR) for the presence of torovirus. Torovirus RNA was detected in 43 of the 118 diarrheic samples (36.4%) by RT-PCR with primers designed in the conserved 3' end of the torovirus genome. By EM, torovirus particles were observed in 37 of the 118 specimens (31.4%). All but one of these samples were also positive by RT-PCR. The incidence of torovirus in the asymptomatic control specimens by RT-PCR was only 11.6%. To establish the identity of the particles observed in the diarrheic specimens, five of the amplicons from samples positive by both RT-PCR and EM were cloned and sequenced. Nucleotide sequence analysis revealed that the bovine torovirus found in southern Ontario manifests between 96 and 97% sequence identity to the BRV type 1 strain found in Iowa. This study shows that bovine torovirus is a common virus in the fecal specimens of calves with diarrhea from farms in southern Ontario and thus may be an important pathogen of cattle.

Toroviruses of animals and humans: a review

Toroviruses are a group of enveloped positive-stranded RNA viruses that cause enteric, respiratory, and perhaps generalized infections in animals and humans. Their name refers to their unique morphological features: an elongated bacilliform core with two rounded ends is surrounded by a membrane that may either tightly adhere to or “shrink-wrap” it, without respecting the capsid's rod shape; in the first instance, straight or curved rhabdovirus-like particles are formed, whereas in the latter a biconcave disk results. Torovirus history is brief: the first representative, Berne virus (BEV), was isolated in Berne, Switzerland, in 1972 from a rectal swab taken from a horse with diarrhea 1 week before it died. BEV is the only equine torovirus isolate that replicates in cell culture; since most molecular data have been obtained with this isolate, BEV has been acknowledged as the torovirus prototype. Recognition of toroviruses as a new group of potentially pathogenic viruses came seven years after the discovery of BEV, when morphologically similar particles were discovered by electron microscopy (EM) in stool specimens from calves with severe diarrhea in a dairy herd in Breda, Iowa. Despite repeated attempts, BRV has not been adapted to the growth in cell or tissue culture, a problem which has hampered its biochemical, bio-physical, and molecular characterization. However, its pathogenesis and pathology have been studied in the experimentally infected gnotobiotic calves, showing that BRV infections may cause gastroenteritis. Recently, Vanopdenbosch et al. reported the isolation of a torovirus-like virus from the respiratory tract of calves with pneumonia, suggesting that both enterotropic and pneumotropic bovine toroviruses exist. Besides the established toroviruses of horses and cattle, torovirus-like particles (TVLPs) have been found by EM in different animal species; torovirus antibodies appear to be widespread in higher vertebrates, indicating that these viruses infect a broad range of animal hosts. The possibility of a torovirus infecting humans was first reported in 1984 and has become more likely in view of the recent data. This chapter is intended to update the information about toroviruses, and to describe the similarities and differences with the related coronaviruses.

Detection of bovine torovirus and other enteric pathogens in feces from diarrhea cases in cattle

The objectives of this study were to determine the prevalence of bovine torovirus (BoTV) in bovine fecal samples from diarrhea cases submitted to the Ohio Animal Disease Diagnostic Laboratory (ADDL) and to assess if a relationship exists between BoTV and the other enteric pathogens detected. From November 1999 to May 2001, 259 specimens from 53 calves (< or = 6 months old), 27 young adults (52 years), 125 adults (> or = 2 years), and 54 animals of unknown age were examined by an antigen-capture enzyme-linked immunosorbent assay (ELISA) and reverse transcriptase-polymerase chain reaction (RT-PCR) assay developed to detect BoTV. Testing for other enteric pathogens was performed by ADDL, and the results were analyzed with the BoTV data. The BoTV was detected using ELISA or RT-PCR in 9.7% (25/259) of the clinical samples, 56% (14/25) of which were from calves (P < 0.001) representing 26.4% (14/53) of the calves tested. Of the BoTV-positive calves, 71% (10/14) were less than 3 weeks of age. In 11/25 positive specimens, BoTV was the only pathogen detected among those examined. Other enteric organisms detected alone or in combination with BoTV in calf samples were rotavirus, coronavirus, Salmonella spp., Cryptosporidium spp., and Giardia spp.; but no consistent association between BoTV and these organisms was observed. In summary, BoTV was detected in fecal samples from cattle with diarrhea, principally in young calves less than 3 weeks of age. Future studies of infectious diarrhea in cattle should also include assays for this etiologic agent.

Enteric and nasal shedding of bovine torovirus (Breda virus) in feedlot cattle

OBJECTIVE

To assess fecal and nasal shedding patterns of bovine torovirus (BoTV) in cattle at time of arrival and periodically throughout the first 21 days after arrival at a feedlot.

ANIMALS

57 steers.

PROCEDURE

Fecal and nasal-swab samples collected on days 0, 4, 14, and 21 after arrival were tested for BoTV, using ELISA. A subset of samples from calves testing positive and negative for BoTV was analyzed, using reverse transcriptase-polymerase chain reaction (RT-PCR). Paired serum samples were collected on days 0 and 21 and tested for BoTV antibodies, using a hemagglutination inhibition assay.

RESULTS

Overall rate of fecal shedding of BoTV was 21 of 57 (37%) by ELISA and 40 of 42 (95%) by RT-PCR with peak shedding on day 4. Diarrhea was more common in calves shedding BoTV than those not shedding the virus (odds ratio, 1.72). Overall rate of nasal shedding of BoTV was 15 of 57 (26%) by ELISA and 42 of 42 (100%) by RT-PCR, with peak shedding on day 0. Specificity of the RT-PCR product was confirmed by sequence analysis. Approximately 93% of the calves seroconverted to BoTV (> 4-fold increase in titer). Differences were not detected between calves shedding BoTV and nonshedders in relation to disease and treatments, perhaps because of the low number of cattle in the study.

CONCLUSIONS AND CLINICAL RELEVANCE

This study confirmed BoTV infections in feedlot cattle, including BoTV antigen and viral RNA in nasal secretions, and the shedding pattern during the first 21 days after arrival in a feedlot.

Detection of bovine torovirus in neonatal calf diarrhoea in Lower Austria and Styria (Austria)

Faeces of 230 calves with and without diarrhoea collected during the winter period 2004/2005 in 100 Austrian farms (Styria and Lower Austria) were examined for viral, bacterial and parasitic enteropathogens. Torovirus‐specific nucleic acid confirmed by reverse transcriptase‐polymerase chain reaction was found in 12 of 230 calves (5.2%). Ten of these calves were clinically ill, several of them showing signs of dehydration and abnormal faecal consistency at the time of sampling. Computer assisted analysis of two nucleotide sequences obtained from Austrian bovine samples revealed 93% similarity to Breda strain, but only 71% or 52% similarity to Equine Berne or Porcine Markelo torovirus strains respectively. Phylogenetic analysis grouped Austrian torovirus samples into the Bovine torovirus cluster indicating the first detection of Bovine torovirus in Austria. In addition, the following agents were detected in bovine faecal samples: Bovine coronavirus, 25.7%; Escherichia coli, 17%; Cryptosporidium spp., 11.7%; Eimeria spp., 10.4%; Rotavirus, 9.1%; Clostridium perfringens, 9.1% and Giardia spp., 6.1%. Salmonella spp. was not detected.

Bovine torovirus (Breda virus) revisited

Bovine torovirus (BoTV) is a pleomorphic virus with a spike-bearing envelope and a linear, non-segmented, positive-sense single-stranded RNA genome. This kidney-shaped virus is associated with diarrhea in calves and apparently has a worldwide distribution. This review provides details of the history and taxonomy of BoTV since its discovery in 1979. Information about virion morphology and architecture, antigenic and biological properties, viral genome, protein composition, thermal and chemical stability, and pH and proteolytic enzymes resistance is also summarized. A major focus of this review is to postulate a possible epidemiological cycle for BoTV, based on epidemiological data obtained in our studies and other published data, and progressing from the newborn calf to the adult animal. The distribution, host range, pathogenesis, disease and clinical signs (under experimental and natural exposure), pathology, diagnosis, prevention, treatment and control of BoTV infections are also described. In addition, a discussion of the zoonotic implications of torovirus-like particles detected in patients with gastroenteritis that resemble and cross-react with BoTV is presented. Hopefully, the findings described here will alert others to the existence of BoTV in cattle and its contribution to the diarrheal disease complex. This review also highlights the need for continual vigilance for potential zoonotic viruses belonging to the order Nidovirales, such as the SARS coronavirus.

First isolation of cytopathogenic bovine torovirus in cell culture from a calf with diarrhea

A cytopathogenic virus (designated the Aichi/2004 strain) was isolated in a human rectal adenocarcinoma cell line (HRT-18) from the ileum contents of a calf with diarrhea. Oval and elongated particles, approximately 100 to 170 nm in diameter, with club-shaped projections were seen in the infected culture supernatant, and torovirus-like (tubular and torus nucleocapsid) structures were seen in the infected cells by electron microscopy. An antiserum against bovine torovirus (BToV) reacted with the infected cells by immunofluorescence and neutralized the isolate. However, antisera against bovine coronavirus (BCV) failed to react with the infected cells by immunofluorescence or did not neutralize the isolate. Further, the isolate was positive for BToV by reverse transcription-PCR (RT-PCR) targeting fragments of the nucleocapsid (N), membrane (M), and spike (S) genes. Comparison of the nucleotide sequences of the PCR products with those of the published N, M, and S genes (476 to 497, 672, and 687 to 690 nucleotides, respectively) of toroviruses showed high sequence identities (up to 99.4%, 98.7%, and 94.9% for the N, M, and S genes, respectively) between the isolate and BToVs. In contrast, the isolate was negative for BCV by RT-PCR. In a serological survey of serum samples from 355 calves at 33 farms, 92% of calves were positive for neutralizing antibodies to the isolate. These results indicate that the isolate in this study was BToV and that BToV infection might be common in cattle in Japan. To our knowledge, this is the first isolation of BToV in tissue culture.

Torovirus detection in faecal specimens of calves and pigs in Hungary: short communication

Bovine torovirus is an established aetiological agent of disease in cattle, while porcine torovirus has only been isolated from healthy animals. Evidence for the presence of torovirus has been described in several European countries and also in the United States. A survey was performed to detect toroviruses in Hungary by means of sampling ten swine and nine bovine herds. Rectal swabs and faecal specimens were collected from diarrhoeic calves and from weaned piglets. The samples were tested by the reverse transcription-polymerase chain reaction (RT-PCR) using torovirus-specific primers and the positive samples were further examined by electron microscopy (EM). Torovirus was detected in 4 diarrhoeic calves (out of 111) and in 10 healthy weaned pigs (out of 200 tested), representing two of the 9 calf herds and two of the 10 pig herds tested. This is the first report of exact diagnosis of torovirus in Hungary.

Association of enteric shedding of bovine torovirus (Breda virus) and other enteropathogens with diarrhea in veal calves

OBJECTIVE

To determine the prevalence, fecal shedding pattern, and association of bovine torovirus (BoTV) with diarrhea in veal calves at time of arrival and periodically throughout the first 35 days after their arrival on a veal farm.

ANIMALS

62 veal calves.

PROCEDURE

Fecal samples collected on days 0, 4, 14, and 35 after arrival were tested for BoTV by use of ELISA and reverse transcriptase-polymerase chain reaction (RT-PCR) assay. Paired serum samples obtained from blood collected on days 0 and 35 were analyzed for BoTV antibodies with a hemagglutination inhibition assay. Fecal samples were also screened for other enteric pathogens, including rotavirus, coronavirus, and Cryptosporidium spp.

RESULTS

Fecal shedding of BoTV was detected in 15 of 62 (24%) calves by use of ELISA and RT-PCR assay, with peak shedding on day 4. A significant independent association between BoTV shedding and diarrhea was observed. In addition, calves shedding > or = 2 enteric pathogens were more likely to have diarrhea than calves shedding < or = 1 pathogen. Calves that were seronegative or had low antibody titers against BoTV (< or = 1:10 hemagglutination inhibition units) at arrival seroconverted to BoTV (> 4-fold increase in titer); these calves were more likely to shed virus than calves that were seropositive against BoTV at arrival.

CONCLUSIONS AND CLINICAL RELEVANCE

Shedding of BoTV was strongly associated with diarrhea in neonatal veal calves during the first week after arrival at the farm. These data provide evidence that BoTV is an important pathogen of neonatal veal calves.

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.

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.

Epidemiological analysis of bovine torovirus in Japan

Bovine torovirus (BToV), a member of the Coronaviridae family, is an established gastrointestinal infectious agent in cattle. No epidemiological research on BToV has been reported from Japan. In this study, we performed a survey to detect BToV in Japan in 2004 and 2005 using 231 fecal samples (167 from diarrheic cattle and 64 from asymptomatic cattle) that were analyzed by nested reverse transcription (RT) PCR using primers located in the consensus sequences of the reported BToV nucleocapsid (N), membrane (M), and spike (S) genes. BToV N, M, and S genes were detected in 6.5% (15/231), 6.1% (14/231), and 5.6% (13/231) of samples by nested-RT-PCR, respectively. In conclusion, detectability was improved compared to the results of the first round of RT-PCR. BToV was detected at a significantly higher rate in diarrheic samples than in asymptomatic samples (14/167 diarrheic samples [8.4%] and 1/64 asymptomatic samples [1.6%]), suggesting that BToV may act as a risk factor for diarrhea in Japanese cattle. The nucleotide sequence of M fragments from the BToV isolates including the newly identified Japanese isolates showed more than 97% identity. A similar degree of homology was observed in the N gene fragment among BToV isolates with the exception of BRV-1 and BRV-2. Domestic samples were classified into three clusters by phylogenetic analysis of the S gene fragment, which were considerably correlated with the geographic origin of the samples. BToV positive areas did not adjoin each other but were spread across a wide range, suggesting that BToV exists conventionally in Japan and is geographically differentiated. We also developed an RFLP method to distinguish these clusters using two restriction enzymes, HaeIII and AccI. This method should be useful for comparing newly acquired BToV-positive samples with the reported BToVs.

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.

Molecular epidemiology of Porcine torovirus (PToV) in Sichuan Province, China: 2011-2013

BACKGROUND

Porcine torovirus (PToV) is a member of the genus Torovirus which is responsible for gastrointestinal disease in both human beings and animals with particular prevalence in youth. Torovirus infections are generally asymptomatic, however, their presence may worsen disease consequences in concurrent infections with other enteric pathogens.

METHODS

A total of 872 diarrheic fecal samples from pigs of different ages were collected from 12 districts of Sichuan Province in the southwest of China. RT-PCR was done with PToV S gene specific primers to detect the presence of PToV positive samples. M gene specific primers were used with the PToV positive samples and the genes were sequenced. A phylogenetic tree was constructed based on the M gene nucleotide sequences from the 19 selected novel Sichuan strains and 21 PToV and BToV M gene sequences from GenBank.

RESULTS

A total of 331 (37.96%, 331/872) samples were found to be positive for PToV and the highest prevalence was observed in piglets aged from 1 to 3 weeks old. Through phylogenetic inference the 40 PToV M gene containing sequences were placed into two genotypes (I & II). The 19 novel Sichuan strains of genotype I showed strong correlations to two Korean gene sequences (GU-07-56-11 and GU-07-56-22). Amino-acid sequence analysis of the 40 PToV M gene strains revealed that the M gene protein was highly conserved.

CONCLUSIONS

This study uncovered the presence of PToV in Sichuan Province, and demonstrated the need for continuous surveillance PToV of epidemiology.

Evolution and homologous recombination of the hemagglutinin-esterase gene sequences from porcine torovirus

The objective of the present study was to gain new insights into the evolution, homologous recombination, and selection pressures imposed on the porcine torovirus (PToV), by examining the changes in the hemagglutinin-esterase (HE) gene. The most recent common ancestor of PToV was estimated to have emerged 62 years ago based upon HE gene sequence data obtained from PToV isolates originating from Spain, South Korea, Netherlands, Hungary, and Italy and using the HE gene of Bovine torovirus isolates Niigata1 (AB661456) and Niigata3 (AB661458) as outgroups. The HE gene sequence data segregated all the PToV isolates into two well-supported monophyletic groups; however, various isolates from Spain, Italy, and South Korea did not segregate geographically suggesting very recent translocation of the viruses to these localities. Evidence of recombination was observed between two South Korean isolates that partitioned into two distinct subclades. Data further suggest that most of the nucleotides in the HE gene are under negative selection; however, changes within codon 237 showed an evidence of positive selection.

Comparison of ELISA and RT-PCR versus immune electron microscopy for detection of bovine torovirus (Breda virus) in calf fecal specimens

Bovine Torovirus (BoTV) is an uncultivable enteric pathogen of cattle. Its failure to grow in vitro limits epidemiological studies, characterization of the virus, and development of diagnostic techniques. The objectives of this study were to develop and standardize an antigen-capture enzyme-linked immunosorbent assay (ELISA) and a reverse transcriptase-polymerase chain reaction (RT-PCR) assay for the detection of BoTV in fecal specimens. These assays were compared with immunoelectron microscopy (IEM) to evaluate their sensitivity, specificity, and efficiency as well as their advantages and limitations. Additionally, several methods to calculate ELISA cutoff values were used and compared using a statistical approach to obtain the optimal cutoff value for the ELISA. A plate cutoff ELISA value was determined to be the best method to calculate the cutoff value. The ELISA and RT-PCR assays developed in this study identified BoTV antigen and viral nucleic acids in feces without cross-reactions with the other calf enteric viruses examined. Both assays showed good agreement with IEM, with a Kappa value of 0.86 for ELISA and 0.85 for RT-PCR. The latter exhibited the higher analytical sensitivity. On the basis of the results obtained in this study, it is recommended that no single test should be used alone in an epidemiological survey because of the observed limitations of each assay. The fast and inexpensive ELISA combined with the highly specific and sensitive RT-PCR are a practical approach for future epidemiological studies of BoTV. These results should provide other researchers with the information needed to develop similar diagnostic assays for the study of BoTV.

Seroprevalence of porcine torovirus (PToV) in Spanish farms

BACKGROUND

Torovirus infections have been associated with gastroenteritis and diarrhea in horses, cows, pigs and humans, especially in young animals and in children. Although asymptomatic in a large percentage of cases, however toroviruses may pose a potential threat to worsen disease outcome in concurrent infections with other enteric pathogens. Previous studies based on the analysis of limited numbers of samples indicated high seroprevalences against porcine torovirus (PToV) in various European countries. The aim of this work was to perform a seroepidemiological survey of PToV in Spanish farms in order to define the seroprevalence against this virus.

RESULTS

Serum samples (n = 2664) from pigs of different ages were collected from 100 Spanish farms coming from 10 regions that concentrate 96.1% of the 3392 farms with 80 or more sows censused in Spain. Samples were screened by means of an indirect enzyme-linked immune-sorbent assay (ELISA) based on a recombinant PToV nucleocapsid protein as antigen. The analysis of the whole serum collection yielded a total of 95.7% (2550/2664) seropositive samples. The highest prevalence (99.6%, 1382/1388) and ELISA values (average O.D. ± standard deviation) were observed in the sows (1.03±0.36) and the lowest prevalence (59.4%, 98/165) and anti-PToV IgG levels (0.45±0.16) were found amongst 3-week-old piglets. Both ELISA reactivity values and seroprevalence percentages rose quickly with piglet's age from 3 to 11 weeks of age; the seroprevalence was 99.3% (2254/2270) when only the samples from sows and pigs over 11-weeks of age were considered. Antibodies against PToV were detected in all analyzed farms.

CONCLUSIONS

This report describes the results of the largest torovirus seroepidemiological survey in farmed swine performed so far. Overall, the seroprevalence against PToV in animals older than 11 weeks of age was >99%, indicating that this virus is endemic in pig herds from Spain.

Complete genome sequencing and genetic analysis of a Japanese porcine torovirus strain detected in swine feces

We sequenced the complete genome of a porcine torovirus (PToV) strain from Japan for the first time. Whole-genome analysis revealed that this strain (Iba/2018) has a mosaic sequence composed of at least three genome backgrounds, related to US, Chinese and German PToV strains. Clear recombination breakpoints were detected in the M and HE coding regions. A similarity plot and structural analysis demonstrated that the HE coding region exhibits the highest diversity, and the most sequence variation was found in the lectin domain. PToVs were divided into two lineages in the HE region, whereas clear lineages were not found in other regions.

First detection and genomic characteristics of bovine torovirus in dairy calves in China

Bovine torovirus (BToV) is a diarrhea-causing pathogen. In this study, 92 diarrheic fecal samples from five farms in four provinces in China were collected and tested for BToV using a RT-PCR assay, and 21.73% samples were found to be BToV positive. Moreover, two complete BToV genome sequences (MN073058 and MN073059) were obtained from the clinical samples, which were 28,297 and 28,301 nucleotides in length, respectively. Sequence analysis showed that the two isolates shared 10 identical amino acid mutations in the S protein compared to the complete S sequences of BToV available in the GenBank database. In addition, seven consecutive amino acid mutations were found from aa 1,486 to 1,492 in the S protein of isolate MN073058. Moreover, the two isolates shared one identical amino acid mutation in the receptor binding sites of the HE protein. To the best of our knowledge, this is the first report on the epidemic and genomic characterization of BToV in China, which is helpful for further understanding the genetic evolution of BToV.

[A review of porcine torovirus research: etiology and epidemiology]

Porcine Torovirus (PToV) is widely distributed in the world with high prevalence rate in swinery. Due to the high detection rate in diarrhea pigs, PToV is thought to be a potential pathogen of swine diarrhea. In recent years, epidemic outbreaks of diarrhea with high morbidity and mortality in China have caused great economic losses. Intertypic recombination events and antigenic cross-reactivity among toroviruses implies potential zoonotic transmission of PToV. The review represented the development history of PToV and made a brief summary of the features in genome and protein epidemiology and laboratory diagnosis of the PToV, and so on.

Progress of research on coronaviruses and toroviruses in large domestic animals using reverse genetics systems

The generation of genetically engineered recombinant viruses from modified DNA/RNA is commonly referred to as reverse genetics, which allows the introduction of desired mutations into the viral genome. Reverse genetics systems (RGSs) are powerful tools for studying fundamental viral processes, mechanisms of infection, pathogenesis and vaccine development. However, establishing RGS for coronaviruses (CoVs) and toroviruses (ToVs), which have the largest genomes among vertebrate RNA viruses, is laborious and hampered by technical constraints. Hence, little research has focused on animal CoVs and ToVs using RGSs, especially in large domestic animals such as pigs and cattle. In the last decade, however, studies of porcine CoVs and bovine ToVs using RGSs have been reported. In addition, the coronavirus disease-2019 pandemic has prompted the development of new and simple CoV RGSs, which will accelerate RGS-based research on animal CoVs and ToVs. In this review, we summarise the general characteristics of CoVs and ToVs, the RGSs available for CoVs and ToVs and the progress made in the last decade in RGS-based research on porcine CoVs and bovine ToVs.

Detection and Genetic Characterization of Bovine Torovirus in Uruguay

Bovine torovirus (BToV) is an enteric pathogen that may cause diarrhea in calves and adult cattle, which could result in economic losses due to weight loss and decreased milk production. This study aimed to report the presence, the genetic characterization and the evolution of BToV in calves in Uruguay. BToV was detected in 7.9% (22/278) of fecal samples, being identified in dairy (9.2%, 22/239) but not beef (0.0%, 0/39) calves. BToV was detected in both diarrheic (14%, 6/43) and non-diarrheic (13.2%, 5/38) dairy calves. In addition, BToV was detected in the intestinal contents of 14.9% (7/47) of naturally deceased dairy calves. A complete genome (28,446 nucleotides) was obtained, which was the second outside Asia and the first in Latin America. In addition, partial S gene sequences were obtained to perform evolutionary analyses. Nucleotide and amino acid substitutions within and between outbreaks/farms were observed, alerting the continuous evolution of the virus. Through Bayesian analysis using BEAST, a recent origin (mid-60s) of BToV, possibly in Asia, was estimated, with two introductions into Uruguay from Asia and Europe in 2004 and 2013, respectively. The estimated evolutionary rate was 1.80 × 10-3 substitutions/site/year. Our findings emphasize the importance of continued surveillance and genetic characterization for the effective management and understanding of BToV's global epidemiology and evolution.