Intestinal mucin-type O-glycans: the major players in the host-bacteria-rotavirus interactions

Rotavirus (RV) causes severe diarrhea in young children and animals worldwide. Several glycans terminating in sialic acids (SAs) and histo-blood group antigens (HBGAs) on intestinal epithelial cell (IEC) surface have been recognized to act as attachment sites for RV. IECs are protected by the double layer of mucus of which O-glycans (including HBGAs and SAs) are a major organic component. Luminal mucins, as well as bacterial glycans, can act as decoy molecules removing RV particles from the gut. The composition of the intestinal mucus is regulated by complex O-glycan-specific interactions among the gut microbiota, RV and the host. In this review, we highlight O-glycan-mediated interactions within the intestinal lumen prior to RV attachment to IECs. A better understanding of the role of mucus is essential for the development of alternative therapeutic tools including the use of pre- and probiotics to control RV infection.

Glycan-mediated interactions between bacteria, rotavirus and the host cells provide an additional mechanism of antiviral defence

Limited efficacy of rotavirus (RV) vaccines in children in developing countries and in animals remains a significant problem necessitating further search for additional approaches to control RV-associated gastroenteritis. During cell attachment and entry events, RV interacts with cell surface O-glycans including histo-blood group antigens (HBGAs). Besides modulation of the protective immunity against RV, several commensal and probiotic bacteria were shown to express HBGA-like substances suggesting that they may affect RV attachment and entry into the host cells. Moreover, some beneficial bacteria have been shown to possess the ability to bind host HBGAs via sugar specific proteins called lectins. However, limited research has been done to evaluate the effects of HBGA-expressing and/or HBGA-binding bacteria on RV infection. The aim of this study was to investigate the ability of selected commensal and probiotic bacteria to bind different RV strains via HBGAs and to block RV infection of IPEC-J2 cells. Our data indicated that Gram-negative probiotic Escherichia coli Nissle 1917 (E. coli Nissle 1917) and commensal Gram-positive (Streptococcus bovis and Bifidobacterium adolescentis) and Gram-negative (Bacteroides thetaiotaomicron, Clostridium clostridioforme and Escherichia coli G58 (E. coli G58) bacteria of swine origin expressed HBGAs which correlated with their ability to bind group A and C RVs. Additionally, Gram-positive E. coli 1917 and E. coli G58 demonstrated the ability to block RV attachment onto IPEC-J2 cells. Taken together, our results support the hypothesis that physical interactions between RVs and HBGA-expressing beneficial bacteria may limit RV replication.

Reduced rotavirus vaccine efficacy in protein malnourished human-faecal-microbiota-transplanted gnotobiotic pig model is in part attributed to the gut microbiota

The low efficacy of human rotavirus (HRV) vaccines in low- and middle-income countries (LMIC) remains a major challenge for global health. Protein-calorie malnutrition (kwashiorkor) affects the gut microbiota and compromises immune development, leading to environmental enteropathy, vaccine failures, and increased susceptibility to enteric diseases in young children. Relationship between diet and reduced vaccine efficacy in developing countries is not well established; therefore, we investigated the interconnections between the host-microbiota-nutrition-HRV vaccine using HRV-vaccinated, human infant faecal microbiota (HIFM)-transplanted neonatal gnotobiotic pigs fed with a protein deficient or sufficient diet. The microbiota from faecal, intestinal (duodenum, ileum, jejunum, and colon), and systemic tissue (liver, spleen, and mesenteric lymph node [MLN]) samples was analysed before and after HRV challenge using MiSeq 16S rRNA sequencing. Overall, microbiota from deficient fed HIFM pigs displayed, compared to the sufficient group, significantly higher Shannon index, especially in the faeces and lower intestines; higher level of Proteus and Enterococcus, and lower level of Bifidobacterium, Clostridium, and Streptococcus in the three types of samples collected (P<0.05); and higher unique operational taxonomic units (OTUs), especially in the systemic tissues. Further, the multivariate analysis between microbiota and immunologic data showed that 38 OTUs at the genus level correlated (r²≤0.5 or ≥-0.5; P<0.05) with at least one host immune response parameter (regulatory [Tregs and transforming growth factor-β], effectors [interferon (IFN)-γ⁺ CD4⁺ and CD8⁺ T cells, IFN-γ and interleukin (IL)-12], and inflammatory [tumour necrosis factor-α, IL-17 and IL-22]) and with opposite trends between diet groups. Differences described above were increased after HRV challenge. We demonstrated that a protein deficient diet affects the composition of the gut microbiota and those changes may further correlate with immune responses induced by HRV and perturbed by the deficient diet. Thus, our findings suggest that the reduced efficacy of HRV vaccine observed in Gn pig model is in part attributed to the altered microbiota composition.

Porcine Coronaviruses

Transmissible gastroenteritis virus (TGEV), porcine epidemic diarrhoea virus (PEDV), and porcine deltacoronavirus (PDCoV) are enteropathogenic coronaviruses (CoVs) of swine. TGEV appearance in 1946 preceded identification of PEDV (1971) and PDCoV (2009) that are considered as emerging CoVs. A spike deletion mutant of TGEV associated with respiratory tract infection in piglets appeared in 1984 in pigs in Belgium and was designated porcine respiratory coronavirus (PRCV). PRCV is considered non-pathogenic because the infection is very mild or subclinical. Since PRCV emergence and rapid spread, most pigs have become immune to both PRCV and TGEV, which has significantly reduced the clinical and economic importance of TGEV. In contrast, PDCoV and PEDV are currently expanding their geographic distribution, and there are reports on the circulation of TGEV-PEDV recombinants that cause a disease clinically indistinguishable from that associated with the parent viruses. TGEV, PEDV and PDCoV cause acute gastroenteritis in pigs (most severe in neonatal piglets) and matches in their clinical signs and pathogenesis. Necrosis of the infected intestinal epithelial cells causes villous atrophy and malabsorptive diarrhoea. Profuse diarrhoea frequently combined with vomiting results in dehydration, which can lead to the death of piglets. Strong immune responses following natural infection protect against subsequent homologous challenge; however, these viruses display no cross-protection. Adoption of advance biosecurity measures and effective vaccines control and prevent the occurrence of diseases due to these porcine-associated CoVs. Recombination and reversion to virulence are the risks associated with generally highly effective attenuated vaccines necessitating further research on alternative vaccines to ensure their safe application in the field.

Epidemiological study of Middle East respiratory syndrome coronavirus infection in dromedary camels in Saudi Arabia, April-May 2015

A cross-sectional study was conducted in five regions in Saudi Arabia to investigate the epidemiology of Middle East respiratory syndrome coronavirus (MERS-CoV) infection in dromedary camels (Camelus dromedarius) during April and May2015. Serum and nasal swab samples were tested for MERS-CoV antibodies andribonucleic acid (RNA) using a recombinant enzyme-linked immunosorbent assay (rELISA) and real-time reverse-transcription polymerase chain reaction (rRT-PCR), respectively. The overall MERS-CoV antibody seroprevalence was 80.5%, whereas the overall viral RNA prevalence was 2.4%. The associations of risk factors with each prevalence were quantified using univariate and multivariate analyses. The multivariate models identified region, age, grazing system, exposure to wild animals and dung removal as factors significantly associated with seroprevalence (p ??0.05). A higher seroprevalence was more likely to occur in camels from the Riyadh, Eastern, Northern and Makkah regions than those from the Jazan region; camels ??4 and 1-3 years of age (marginally significant) than calves < 1 year; and camels raised in zero grazing and semi-open grazing systems than those raised in an open grazing system. However, the presence of wild animals and daily dung removal were negatively associated with seroprevalence. On the other hand, region and sex were significantly associated with MERS-CoV RNA prevalence(p ??0.05). A higher viral RNA prevalence was more likely to occur in camels from the Riyadh region and Eastern region (marginally significant) than in those from the Makkah region, and in male camels than female camels. In conclusion, the risk factors identified in this study can be considered to be predictors of MERS-CoV infection in camels and should be taken into account when developing an efficient and cost-effective control strategy.

Effect of antibiotic, probiotic, and human rotavirus infection on colonisation dynamics of defined commensal microbiota in a gnotobiotic pig model

We developed a gnotobiotic (Gn) pig model colonised with defined commensal microbiota (DMF) to provide a simplified and controlled system to study the interactions between intestinal commensals, antibiotics (ciprofloxacin, CIP), probiotics (Escherichia coli Nissle 1917, EcN) and virulent human rotavirus (VirHRV). The DMF included seven gut commensal species of porcine origin that mimic the predominant species in the infant gut. Gn piglets were divided into four groups: DMF control (non-treated), DMF+CIP (CIP treated), DMF+CIP+EcN (CIP/EcN treated), DMF+EcN (EcN treated) and inoculated orally with 10⁵ cfu of each DMF strain. The pig gut was successfully colonised by all DMF species and established a simplified bacterial community by post-bacteria colonisation day (PBCD) 14/post-VirHRV challenge day (PCD) 0. Overall, Bifidobacterium adolescentis was commonly observed in faeces in all groups and time points. At PCD0, after six days of CIP treatment (DMF+CIP), we observed significantly decreased aerobic and anaerobic bacteria counts especially in jejunum (P<0.001), where no DMF species were detected in jejunum by T-RFLP. Following HRV challenge, 100% of pigs in DMF+CIP group developed diarrhoea with higher diarrhoea scores and duration as compared to all other groups. However, only 33% of pigs treated with EcN plus CIP developed diarrhoea. EcN treatment also enhanced the bacterial diversity and all seven DMF species were detected with a higher proportion of Bifidobacterium longum in jejunum in the DMF+CIP+EcN group on PBCD14/PCD0. Our results suggest that EcN increased the proportion of B. longum especially in jejunum and mitigated adverse impacts of antibiotic use during acute-infectious diarrhoea. The DMF model with a simplified gut commensal community can further our knowledge of how commensals and probiotics promote intestinal homeostasis and contribute to host health.

Molecular and antigenic characterization of bovine Coronavirus circulating in Argentinean cattle during 1994-2010

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Detection rate of BCoV was statistically higher in dairy than in beef calves.

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Argentinean strains are distant from the Mebus strain included in local vaccines.

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In vitro cross-protection between Arg95 field strain and Mebus reference strain.

Bovine coronavirus (BCoV) is an important viral pathogen associated with neonatal calf diarrhea. Our aim was to investigate the incidence of BCoV in diarrhea outbreaks in beef and dairy herds from Argentina during 1994–2010. A total of 5.365 fecal samples from diarrheic calves were screened for BCoV diagnosis by ELISA. The virus was detected in 1.71% (92/5365) of the samples corresponding to 5.95% (63/1058) of the diarrhea cases in 239 beef and 324 dairy farms. The detection rate of BCoV was significantly higher in dairy than in beef herds: 12.13% (29/239) vs. 4.32% (14/324) respectively. Phylogenetic analysis of the hypervariable S1 region of seven representative samples (from different husbandry systems, farm locations and years of sampling) indicated that BCoV strains circulating in Argentinean beef and dairy herds formed a cluster distinct from other geographical regions. Interestingly, Argentinean strains are distantly related (at both the nucleotide and amino acid levels) with the Mebus historic reference BCoV strain included in the vaccines currently available in Argentina. However, Mebus-induced antibodies were capable of neutralizing the BCoV Arg95, a field strain adapted to grow in vitro, and vice versa, indicating that both strains belong to the same CoV serotype reported in cattle. This work represents the first large survey describing BCoV circulation in Argentinean cattle.

Lactobacillus acidophilus and Lactobacillus reuteri modulate cytokine responses in gnotobiotic pigs infected with human rotavirus

Probiotic lactic acid bacteria (LAB) have been shown to alleviate inflammation, enhance the immunogenicity of rotavirus vaccines, or reduce the severity of rotavirus diarrhoea. Although the mechanisms are not clear, the differential Th1/Th2/Th3-driving capacities and modulating effects on cytokine production of different LAB strains may be the key. Our goal was to delineate the influence of combining two probiotic strains of Lactobacillus acidophilus and Lactobacillus reuteri on the development of cytokine responses in neonatal gnotobiotic pigs infected with human rotavirus (HRV). We demonstrated that HRV alone, or HRV plus LAB, but not LAB alone, initiated serum cytokine responses, as indicated by significantly higher concentrations of IFN-α, IFN-γ, IL-12, and IL-10 at postinoculation day (PID) 2 in the HRV only and LAB+HRV+ pigs compared to LAB only and LAB-HRV- pigs. Peak cytokine responses coincided with the peak of HRV replication. LAB further enhanced the Th1 and Th2 cytokine responses to HRV infection as indicated by significantly higher concentrations of IL-12, IFN-γ, IL-4 and IL-10 in the LAB+HRV+ pigs compared to the LAB-HRV+ pigs. The LAB+HRV+ pigs maintained relatively constant concentrations of TGF-β compared to the HRV only group which had a significant increase at PID 2 and decrease at PID 7, suggesting a regulatory role of LAB in maintaining gut homeostasis. At PID 28, cytokine secreting cell (CSC) responses, measured by ELISpot, showed increased Th1 (IL-12, IFN-γ) CSC numbers in the LAB+HRV+ and LAB-HRV+ groups compared to LAB only and LAB-HRV- pigs, with significantly increased IL-12 CSCs in spleen and PBMCs and IFN-γ CSCs in spleen of the LAB+HRV+ group. Thus, HRV infection alone, but not LAB alone was effective in inducing cytokine responses but LAB significantly enhanced both Th1 and Th2 cytokines in HRV-infected pigs. LAB may also help to maintain immunological homeostasis during HRV infection by regulating TGF-β production.

Fate and transport of zoonotic, bacterial, viral, and parasitic pathogens during swine manure treatment, storage, and land application

Members of the public are always somewhat aware of foodborne and other zoonotic pathogens; however, recent illnesses traced to produce and the emergence of pandemic H1N1 influenza virus have increased the scrutiny on all areas of food production. The Council for Agricultural Science and Technology has recently published a comprehensive review of the fate and transport of zoonotic pathogens that can be associated with swine manure. The majority of microbes in swine manure are not zoonotic, but several bacterial, viral, and parasitic pathogens have been detected. Awareness of the potential zoonotic pathogens in swine manure and how treatment, storage, and handling affect their survival and their potential to persist in the environment is critical to ensure that producers and consumers are not at risk. This review discusses the primary zoonotic pathogens associated with swine manure, including bacteria, viruses, and parasites, as well as their fate and transport. Because the ecology of microbes in swine waste is still poorly described, several recommendations for future research are made to better understand and reduce human health risks. These recommendations include examination of environmental and ecological conditions that contribute to off-farm transport and development of quantitative risk assessments.

Cytokine and antibody responses in gnotobiotic pigs after infection with human norovirus genogroup II.4 (HS66 strain)

A human norovirus genogroup II.4 strain HS66 (HuNoV-HS66) infects and causes mild diarrhea in gnotobiotic (Gn) pigs (S. Cheetham, M. Souza, T. Meulia, S. Grimes, M. G. Han, and L. J. Saif, J. Virol. 80:10372-10381, 2006). In this study we evaluated systemic and intestinal humoral and cellular immune responses to HuNoV-HS66 in orally inoculated pigs. Antibodies and type I interferon (IFN-I or IFN-alpha), proinflammatory interleukin-6 (IL-6), Th1 (IL-12 and IFN-gamma), Th2 (IL-4), and Th2/regulatory T ([T(reg)] IL-10) cytokine profiles in serum and intestinal contents (IC) of the HuNoV-HS66-inoculated pigs and controls were assessed by enzyme-linked immunosorbent assay at selected postinoculation days (0 to 28). Using an enzyme-linked immunospot assay, we evaluated immunoglobulin M (IgM), IgA, and IgG antibody-secreting cells (ASC) and cytokine-secreting cells (CSC) in intestine, spleen, and blood. In the HuNoV-inoculated pigs, antibody titers in serum and IC were generally low, and 65% seroconverted. Pigs with higher diarrhea scores were more likely to seroconvert and developed higher intestinal IgA and IgG antibody titers. The numbers of IgA and IgG ASC were higher systemically than in the gut. In serum, HuNoV induced persistently higher Th1 (low transient IFN-gamma and high IL-12) than the other cytokines, but also low Th2 (IL-4) and Th2/T(reg) (IL-10) levels; low, transient proinflammatory (IL-6) cytokines; and, notably, a delayed IFN-alpha response. In contrast, intestinal innate (IFN-alpha early and late) and Th1 (IL-12 late) cytokines were significantly elevated postinfection. HuNoV-HS66 also elicited higher numbers of Th1 (IL-12 and IFN-gamma) CSC than Th2 (IL-4) and proinflammatory (IL-6) CSC, with the latter responses low in blood and intestine, reflecting low intestinal inflammation in the absence of gut lesions. These data provide insights into the kinetics of cytokine secretion in serum and IC of HuNoV-inoculated Gn pigs and new information on intestinal humoral and cellular immune responses to HuNoV that are difficult to assess in human volunteers.

Dual enteric and respiratory tropisms of winter dysentery bovine coronavirus in calves

Although winter dysentery (WD), which is caused by the bovine coronavirus (BCoV) is characterized by the sudden onset of diarrhea in many adult cattle in a herd, the pathogenesis of the WD-BCoV is not completely understood. In this study, colostrum-deprived calves were experimentally infected with a Korean WD-BCoV strain and examined for viremia, enteric and nasal virus shedding as well as for viral antigen expression and virus-associated lesions in the small and large intestines and the upper and lower respiratory tract from 1 to 8 days after an oral infection. The WD-BCoV-inoculated calves showed gradual villous atrophy in the small intestine and a gradual increase in the crypt depth of the large intestine. The WD-BCoV-infected animals showed epithelial damage in nasal turbinates, trachea and lungs, and interstitial pneumonia. The WD-BCoV antigen was detected in the epithelium of the small and large intestines, nasal turbinates, trachea and lungs. WD-BCoV RNA was detected in the serum from post-inoculation day 3. These results show that the WD-BCoV has dual tropism and induces pathological changes in both the digestive and respiratory tracts of calves. To our knowledge, this is the first detailed report of dual enteric and respiratory tropisms of WD-BCoV in calves. Comprehensive studies of the dual tissue pathogenesis of the BCoV might contribute to an increased understanding of similar pneumoenteric CoV infections in humans.

Cytokine responses in gnotobiotic pigs after infection with virulent or attenuated human rotavirus

To understand the role of cytokines during rotavirus infection, we assessed the kinetics of tumor necrosis factor alpha (TNF-alpha) and interleukin-6 (IL-6) (proinflammatory), IL-12 (Th1 inducer), gamma interferon (IFN-gamma) (Th1), IL-4 and IL-10 (Th2), and transforming growth factor beta (Th3) cytokine responses by enzyme-linked immunosorbent assay in serum and intestinal contents of neonatal gnotobiotic pigs and IL-12, IFN-gamma, IL-4, and IL-10 cytokine-secreting cell (CSC) responses of mononuclear cells from ileum, spleen, and blood by ELISPOT. Pigs received the virulent Wa P1A[8]G1 strain of human rotavirus (HRV) (VirHRV), attenuated Wa HRV (AttHRV), or mock (controls). The TNF-alpha levels peaked earlier and remained elevated in serum of the VirHRV group but peaked later in the AttHRV group. In serum, IL-6 was significantly elevated at postinoculation day (PID) 1 in the VirHRV group and at PID 3 in both HRV groups. The IL-12 was detected in serum of all pigs including controls with significantly elevated peaks in both HRV-infected groups, indicating a role for IL-12 in the induction of immune responses to rotavirus infection. Only low and transient IFN-gamma responses occurred in serum and intestinal contents of the AttHRV-infected pigs, compared to significantly higher and prolonged IFN-gamma responses in the VirHRV-infected pigs. This observation coincides with the diarrhea and viremia induced by VirHRV. The number of IFN-gamma-secreting cells was significantly higher in the ileum of the VirHRV group than in that of the controls. The number of IL-4 CSCs was significantly higher in ileum of both HRV groups than in that of the controls. Significantly higher levels of IL-10 in the serum occurred early in the VirHRV group, compared to lower levels in the AttHRV group. However, the number of IL-10 CSCs was significantly higher later in ileum and spleen of the AttHRV than in the VirHRV group, suggesting a delayed initiation of a Th2 response induced by AttHRV. A significantly higher percentage of pigs had IFN-gamma and IL-10 responses in serum after VirHRV infection than after AttHRV infection or in controls. These data indicate a balanced Th1/Th2 response during rotavirus infection, with higher cytokine levels early after infection with VirHRV compared to that with AttHRV. Mapping the kinetics and patterns of cytokine responses after rotavirus infection has important implications for induction of protective immunity by HRV vaccines. Higher protection rates may be associated with more balanced Th1- and Th2-type responses, but induction of higher earlier IFN-gamma (Th1) and proinflammatory cytokines triggered by VirHRV may also play an important role in the higher intestinal immunoglobulin A responses and protection rates induced by VirHRV.

Binding patterns of human norovirus-like particles to buccal and intestinal tissues of gnotobiotic pigs in relation to A/H histo-blood group antigen expression

Histo-blood group antigen (HBGA) phenotypes have been associated with susceptibility to human noroviruses (HuNoVs). Our aims were: (i) to determine the patterns of A/H HBGA expression in buccal and intestinal tissues of gnotobiotic (Gn) pigs; (ii) to determine if virus-like particles (VLPs) of HuNoV genogroup I (GI) and GII bind to A- or H-type tissues; (iii) to compare A/H expression and VLP binding patterns and confirm their binding specificities by blocking assays; (iv) to develop a hemagglutination inhibition test using buccal cells from live pigs to determine the Gn pig's A/H phenotype and to match viral strains with previously determined HuNoV VLP binding specificities; and (v) to determine the A/H phenotypes and compare these data to the infection outcomes of a previous study of 65 Gn pigs inoculated with HuNoV GII/4 strain HS66 and expressing A and/or H or neither antigen on their buccal and intestinal tissues (S. Cheetham, M. Souza, T. Meulia, S. Grimes, M. G. Han, and L. J. Saif, J. Virol. 80:10372-10381, 2006). We found that the HuNoV GI/GII VLPs of different clusters bound to tissues from four pigs tested (two A+ and two H+). The GI/1 and GII/4 VLPs bound extensively to duodenal and buccal tissues from either A+ or H+ pigs, but surprisingly, GII/1 and GII/3 VLPs bound minimally to the duodenum of an A+ pig. The VLP binding was partially inhibited by A-, H1-, or H2-specific monoclonal antibodies, but was completely blocked by porcine mucin. Comparing the A/H phenotypes of 65 HS66-inoculated Gn pigs from our previous study, we found that significantly more A+ and H(+) pigs (51%) than non-A+ and non-H+ pigs (12.5%) shed virus. From the 22 convalescent pigs, significantly more A+ or H+ pigs (66%) than non-A+ or H+ pigs (25%) seroconverted.

Self-assembly of the recombinant capsid protein of a bovine norovirus (BoNV) into virus-like particles and evaluation of cross-reactivity of BoNV with human noroviruses

None of the enteric caliciviruses except Po/Sapo/GIII/Cowden/80/US replicates in cell culture, which complicates efforts to develop control strategies or to study viral replication. To develop serological assays for bovine noroviruses (BoNVs) and to determine the cross-reactivity of BoNV with human noroviruses, we generated two recombinant baculoviruses, rCV186-OH and rJNCV, to express the capsid genes of Bo/CV186-OH/00/US (Norovirus genogroup III [GIII], genotype 2 [GIII/2]). rCV186-OH expressed the expected 57-kDa capsid protein, but rJNCV expressed a truncated capsid protein of 35 kDa. Sequence analysis of rJNCV identified a single nucleotide deletion in the P domain of the capsid gene, which introduced a stop codon at amino acid 323. The recombinant capsid protein produced by rCV186-OH but not that produced by rJNCV self-assembled into virus-like particles (VLPs) similar to native BoNV. An antibody-capture enzyme-linked immunosorbent assay (ELISA) and antigen-capture ELISA (Ag-ELISA) detected serum antibody and antigen, respectively, from calves infected with Bo/CV186-OH/00/US but not antibodies or antigens to other enteric viruses. In other tests of the GIII/2 BoNV Ag-ELISA, no cross-reactivity was observed with VLPs from one GI and four GII human noroviruses and porcine sapovirus Cowden strain. Because, like human noroviruses, BoNVs do not grow in cell culture, the BoNV VLPs will be useful in the serological assays described for the detection of BoNV antibody and antigen. Consistent with the phylogenetic analysis of the capsid genes of bovine and human noroviruses (M. G. Han, J. R. Smiley, C. Thomas, and L. J. Saif, J. Clin. Microbiol. 42:5214-5224, 2004), the results suggest that GIII/2 BoNV does not share significant antigenic relationships with the five characterized human noroviruses tested.

Animal coronaviruses: what can they teach us about the severe acute respiratory syndrome?

In 2002, a new coronavirus (CoV) emerged in the People's Republic of China, associated with a severe acute respiratory syndrome (SARS) and mortality in humans. The epidemic rapidly spread throughout the world before being contained in 2003, although sporadic cases occurred thereafter in Asia. The virus is thought to be of zoonotic origin from a wild animal reservoir (Himalayan palm civets [Paguma larvata] are suspected), but the definitive host is unknown. There is concern about possible transmission of SARS CoV to rodents or domestic cats (as proven experimentally) with perpetuation of the disease in these species. In livestock and poultry, CoVs are recognised causes of enteric and respiratory infections that are often fatal in young animals. Although the emergence of SARS surprised the medical community, veterinary coronavirologists had previously isolated CoVs from wildlife and documented their interspecies transmission to livestock. Furthermore, scientists were aware of compelling evidence pointing to the emergence of new CoV strains and the mutation of existing strains resulting in new disease syndromes in animals, but the evolution and disease impact of CoVs was not widely appreciated before SARS. This review focuses on the comparative pathogenesis of CoV infections, including the factors that accentuate CoV respiratory disease, with emphasis on livestock and poultry. The goal is to provide insights into CoV transmission and disease mechanisms that could potentially be applicable to SARS, highlighting the contributions of veterinary scientists to this area of study. Such examples illustrate the need for communication and collaboration between the veterinary and medical communities to understand and control emerging zoonotic diseases of the 21st Century.

Viremia and nasal and rectal shedding of rotavirus in gnotobiotic pigs inoculated with Wa human rotavirus

Respiratory symptoms with rotavirus shedding in nasopharyngeal secretions have been reported in children with and without gastrointestinal symptoms (Zheng et al., 1991, J. Med. Virol. 34:29-37). To investigate if attenuated and virulent human rotavirus (HRV) strains cause upper respiratory tract infections or viremia in gnotobiotic pigs, we inoculated them with attenuated or virulent HRV intranasally, intravenously, or orally or via feeding tube (gavage) and assayed virus shedding. After oral or intranasal inoculation with attenuated HRV, the pigs remained asymptomatic, but 79 to 95% shed virus nasally and 5 to 17% shed virus rectally. After inoculation by gavage, no pigs shed virus nasally or rectally, but all pigs seroconverted with antibodies to HRV. No viremia was detected through postinoculation day 10. Controls inoculated intranasally with nonreplicating rotavirus-like particles or mock inoculated did not shed virus. In contrast, 100% of pigs inoculated with virulent HRV (oral, intranasal, or gavage) developed diarrhea, shed virus nasally and rectally, and had viremia. The infectivity of sera from the viremic virulent HRV-inoculated pigs was confirmed by inoculating gnotobiotic pigs orally with pooled HRV-positive serum. Serum-inoculated pigs developed diarrhea and fecal and nasal virus shedding and seroconverted with serum and intestinal HRV antibodies. Pigs inoculated intravenously with serum or intestinal contents from the viremic virulent HRV-inoculated pigs developed diarrhea, virus shedding, and viremia, similar to the orally inoculated pigs. This study provides new evidence that virulent HRV causes transient viremia and upper respiratory tract infection in addition to gastrointestinal infection in gnotobiotic pigs, confirming previous reports of rotavirus antigenemia (Blutt et al., Lancet 362:1445-1449, 2003). Our data also suggest that intestinal infection might be initiated from the basolateral side of the epithelial cells via viremia. Additionally, virus shedding patterns indicate a different pathogenesis for attenuated versus virulent HRV.

Antibody responses to human rotavirus (HRV) in gnotobiotic pigs following a new prime/boost vaccine strategy using oral attenuated HRV priming and intranasal VP2/6 rotavirus-like particle (VLP) boosting with ISCOM

Safer and more effective human rotavirus (HRV) vaccines are needed. We evaluated oral priming with attenuated WaHRV (AttHRV) followed by boosting with two intranasal (IN) doses of VP2/6 virus-like particles (2/6 VLP) with immunostimulating complexes (ISCOM) to determine if this regimen induces protection against diarrhoea and viral shedding in the gnotobiotic pig model. IgM, IgA and IgG antibody titres in serum and intestinal contents were quantified by enzyme-linked immunosorbent assay (ELISA) and serum neutralizing antibody titres were measured by a virus neutralization (VN) test. Seven groups of neonatal gnotobiotic pigs were vaccinated at post-inoculation days (PID) 0, 10 and 21 and challenged with virulent WaHRV at PID 28. The vaccine groups included: (1, 2) oral priming with AttHRV and boosting with two IN immunizations with 2/6 VLP-ISCOM (Att + 2/6 VLP-ISCOM) at VLP concentrations of 250 micro g or 25 micro g; (3, 4) three IN immunizations with 2/6 VLP-ISCOM at VLP concentrations of 250 micro g or 25 micro g (2/6 VLP-ISCOM); (5) three oral immunizations with AttHRV (3xAttHRV); (6) one oral immunization with AttHRV (1xAttHRV); (7) controls (ISCOM matrix and/or diluent). The pigs that received 3xAttHRV or Att + 2/6 VLP250-ISCOM had the highest protection rates against diarrhoea upon challenge at PID 28 with virulent WaHRV. The IgA antibody titres to HRV in intestinal contents were significantly higher in the Att + 2/6 VLP250-ISCOM group than in all other groups prechallenge (PID 28). Serum VN antibody titres were statistically similar after the first inoculation among the groups given AttHRV, but at PID 28 VN antibody titres were significantly higher for the 3xAttHRV and Att + 2/6 VLP250-ISCOM groups than for the 1xAttHRV group suggesting that boosting with 2/6 VLP also boosted VN antibody responses. In humans, intestinal IgA antibodies have been correlated with protection against symptomatic reinfection. Thus the vaccine regimen of one oral dose of AttHRV and two IN immunizations with 2/6 VLP250-ISCOM may be an alternative to multiple-dose live oral vaccines in humans.

Animal coronavirus vaccines: lessons for SARS

Severe acute respiratory syndrome (SARS) emerged in China and spread globally as a human pandemic. It is caused by a new coronavirus (CoV) of suspect animal origin. The emergence of SARS stunned medical scientists, but veterinary virologists had previously recognized CoVs as causing fatal respiratory or enteric disease in animals with interspecies transmission and wildlife reservoirs. Because of its public health impact, major efforts are focused on development of SARS vaccines. Occurrence of CoV disease at mucosal surfaces necessitates the stimulation of local immunity, having an impact on the vaccine type, delivery and adjuvant needed to achieve mucosal immunity. Such immunity is often short-lived, requires frequent boosting and may not prevent re-infection, all factors complicating CoV vaccine design. SARS vaccine efforts should be enhanced by understanding the correlates of protection and reasons for the success or failure of animal CoV vaccines. This review will focus on studies of immunity and protection in swine to the enteric CoV, transmissible gastroenteritis (TGEV) versus the respiratory variant, porcine respiratory CoV (PRCV), comparing live, inactivated and subunit vaccines, various vaccine vectors, routes and adjuvants. In addition avian infectious bronchitis CoV (IBV) vaccines targeted for protection of the upper respiratory tract of chickens are discussed. Unfortunately, despite long-term efforts, effective vaccines to prevent enteric CoV infections remain elusive, and generally live, but not killed vaccines, have induced the most consistent protection against animal CoVs. Confirmation of the pathogenesis of SARS in humans or animals models that mimic SARS may further aid in vaccine design and evaluation.

Respiratory and fecal shedding of porcine respiratory coronavirus (PRCV) in sentinel weaned pigs and sequence of the partial S-gene of the PRCV isolates

Porcine respiratory coronavirus (PRCV), a spike (S) gene deletion mutant of Transmissible gastroenteritis virus (TGEV), causes mild or subclinical respiratory infections in pigs. The shedding of PRCV/TGEV was studied at different days post-arrival in fecal and nasal swabs from PRCV/TGEV seronegative sentinel pigs introduced into a PRCV seropositive herd with questionable TGEV serology and diarrhea. Nasal shedding of PRCV was detected in 57% and 63% of samples by nested-RT-PCR and cell culture immunofluorescence (CCIF), respectively. However fecal shedding of PRCV was detected in 37% of the samples by nested-RT-PCR and 19% by CCIF. Four respiratory and 5 fecal PRCV strains were isolated in swine testicle cells including nasal/fecal PRCV pairs (isolated at the same time) from 3 pigs. Comparison of nasal/fecal PRCV pairs from individual pigs revealed different deletions in the spike (S) gene (648 or 681 nt) in 2 pairs and a consistent change in nt 790/791 (aa T to V) for all pairs. In preliminary studies, inoculation of gnotobiotic pigs with each plaque-purified pair of the nasal and fecal PRCV isolates, revealed no clinical disease but different tropisms. The nasal isolate was shed both nasally and in feces, but the fecal isolate was shed only marginally in feces, and not nasally. Our results show that nested-RT-PCR was as sensitive as CCIF for PRCV detection in nasal swabs, but was more sensitive than CCIF for PRCV detection in fecal samples; alternatively PRCV shed in feces was more labile with loss of infectivity. The S-gene sequence differences found between the fecal and respiratory PRCV isolates may influence their tissue tropism. These new PRCV isolates should be useful to understand the molecular basis of coronavirus tropism and evolution in infected swine.

Protection and antibody responses to oral priming by attenuated human rotavirus followed by oral boosting with 2/6-rotavirus-like particles with immunostimulating complexes in gnotobiotic pigs

We evaluated antibody responses and protection induced by attenuated Wa human rotavirus (AttHRV) and VP2/6-rotavirus-like particles (VLP), 100 or 250 microg/dose, with immunostimulating complexes (ISCOM) (VLP/ISCOM) each given orally, alone or sequentially to gnotobiotic pigs. The AttHRV-VLP 250 microg/ISCOM and three-dose-AttHRV (AttHRV3x) groups had significantly higher serum IgA, IgG and intestinal IgA antibody titers to HRV pre-challenge than the three-dose-VLP 100 microg/ISCOM group (VLP/ISCOM3x) and controls (diluent/ISCOMmatrix). Protection rates against viral shedding and diarrhea were highest in the AttHRV-VLP250 microg/ISCOM and AttHRV3x groups, lower in the AttHRV-VLP 100 microg/ISCOM group, with no protection in the VLP/ISCOM3x group and controls. Thus, VLP/ISCOM boosted antibody titers and protection after priming with AttHRV.

Reverse transcription-PCR assays for detection of bovine enteric caliciviruses (BEC) and analysis of the genetic relationships among BEC and human caliciviruses

Two genetically distinct bovine enteric caliciviruses (BECs) have been identified: the norovirus (NLV) Jena and Newbury Agent-2 (NA-2) BECs, which are genetically related to human noroviruses, and the Nebraska (NB) BECs, which is related to sapoviruses and lagoviruses but may also represent a new calicivirus genus. The prevalence of these two BEC genotypes in cattle is unknown. Although reverse transcription-PCR (RT-PCR) primers for human NLV recognize NLV-BECs, the genetic relationships between NLV from humans and the NLV-BECs commonly circulating in cattle is undefined. In the present study, veal calf fecal samples were assayed for enteric caliciviruses by using six RT-PCR primer sets designed for the detection of human NLVs or BECs. Caliciviruses genetically related to the NLV-BEC Jena and NA-2 strains or to the recently characterized NB BEC strain were identified in three of four and four of four sampled veal herds, respectively. Extended 3'-terminal genome sequences of two NLV-BECs, designated CV95-OH and CV186-OH, encoding the RNA-dependent RNA polymerase (RdRp; open reading frame 1 [ORF-1]), VP1 (ORF-2), and VP2 (ORF-3) genes were determined. Phylogenetic and sequence identity analyses of each genome region demonstrated these viruses to be most closely related to the NLV-BEC Jena and NA-2 strains. In initial testing, the human P289-P290 (P289/290) primer set was found to be the most sensitive for calicivirus detection. However, its failure to identify all positive fecal pools (as determined by other assays) led us to design two new primer sets, CBECU-F/R and NBU-F/R, for the sensitive and specific detection of NLV-BEC (NLV-BEC Jena and NA-2) and BEC-NB-like viruses, respectively. The RT-PCR assays with the new primers were compared against other primer sets, including P289/290. Composite results of the tests completed by using the new assays identified 72% (54 of 75) of veal calf fecal samples as positive, with 21 of 21 sequenced reaction products specific for the target RdRp gene. The same design strategy used for the new BEC assays may also be applicable to the design of similar assays for the detection of human caliciviruses (HuCVs). Our data support the genetic relationship between NLV-BECs and NLV-HuCVs but with the NLV-BECs comprising two clusters within a third NLV genogroup.

Characterization of an enteropathogenic bovine calicivirus representing a potentially new calicivirus genus

Bovine enteric caliciviruses (BEC) are associated with diarrhea in young calves. The BEC strains detected in Europe form a third genogroup within the genus "Norwalk-like viruses" (NLV) of the family Caliciviridae. In this report, we present sequence, clinical, and histological data characterizing a novel enteropathogenic BEC strain, NB, detected in fecal specimens from calves in the United States. The complete RNA genome of the NB virus is 7,453 bases long and is organized into two open reading frames (ORFs). ORF-1 is 2,210 amino acids long and encodes a large nonstructural polyprotein contiguous with the major capsid protein (VP1), similar to the lagoviruses and "Sapporo-like viruses" (SLV). The conserved calicivirus motifs were identified in the nonstructural proteins. ORF-2 is located at the 3' end of the genome and encodes a small basic protein (VP2) of 225 amino acids. The 5' and 3' untranslated regions are 74 and 67 bases long, respectively. Among caliciviruses, NB virus shows amino acid identities of 14.1 to 22.6% over the entire ORF-1 nonstructural-protein sequence with NLV, SLV, vesivirus, and lagovirus strains, while the overall sequence identity of the complete NB VP-1 with other caliciviruses is low, varying between 14.6 and 26.7%. Phylogenetic analysis of the complete VP1 protein, including strains from all four calicivirus genera, showed the closest grouping of NB virus to be with viruses in the genus Lagovirus, which cause liver infections and systemic hemorrhage in rabbits. In gnotobiotic calves, however, NB virus elicited only diarrhea and intestinal lesions that were most severe in the upper small intestine (duodenum and jejunum), similar to the NLV BEC strains. The tissues of major organs, including the lung, liver, kidney, and spleen, had no visible microscopic lesions.

First isolation of rotavirus associated with neonatal diarrhoea in guanacos (Lama guanicoe) in the Argentinean Patagonia region

Group A rotavirus (RV) and coronavirus (CV) are common viral pathogens associated with neonatal diarrhoea in numerous animal species. The purpose of this work was to investigate the presence of these viral agents in two farm populations of captured guanacos (Lama guanicoe) in the Argentinean Patagonia region, that developed severe diarrhoea outbreaks. Stool and serum samples were analysed for RV and bovine CV antigen and antibody by enzyme‐linked immunosorbent assay. Rotavirus was detected in faeces from two new‐born guanacos with acute diarrhoea, one in each farm. After electrophoretic analysis, each isolated strain, showed a distinctive long dsRNA electropherotype characteristic of group A rotaviruses (4:2:3:2). In addition, 95% (38 of 40) of the sampled animals were positive for RV antibodies, suggesting a high prevalence of RV infection in the populations tested. No evidence of CV circulation by antigen or antibody analysis was observed. To our knowledge, this is the first report of the detection and isolation of RV associated with neonatal diarrhoea in Lama guanicoe.

Lactogenic antibody responses in cows vaccinated with recombinant bovine rotavirus-like particles (VLPs) of two serotypes or inactivated bovine rotavirus vaccines

Triple-layered virus-like particles (VLPs) were produced in a baculovirus expression system from the two prevalent bovine rotavirus (BRV) serotypes, IND (P[5]G6) and 2292B (P[11]G10). Five groups of pregnant cows were inoculated intramuscularly and intramammarily with IND VLPs [BRV RF VP2, and IND VP4, 6, and 7, 250 microg per dose], 2292B VLPs [RF VP2, Cr VP4 (P[11]), and 2292B VP6 and 7, 250 microg per dose], combined IND/2292B VLPs (125 microg each VLP per dose), inactivated IND BRV (5x10(7)PFU per dose, pre-inactivation), or cell supernatant (mock-controls) in incomplete Freund's adjuvant. Serum, colostrum and milk were collected and tested for isotype-specific antibodies, and homologous and heterologous neutralizing antibodies (VN) to BRV by ELISA and VN tests, respectively. After vaccination, the IgG1 and homologous VN geometric mean antibody titers (GMTs) to BRV in serum of vaccinated groups were significantly (P<0.05) higher than in the mock-controls through postpartum day (PPD) 30. In colostrum, the IgG1 and IgA, and the homologous and heterologous VN GMTs of the IND VLP, 2292B VLP, combined IND/2292B VLP and the inactivated IND groups were significantly enhanced compared to the mock-controls, except for the heterologous VN GMTs in the inactivated IND group. However, the VLP vaccine groups had significantly higher homologous and heterologous VN GMTs than the inactivated IND group. The VN GMTs of the IND/2292B VLP group were statistically similar to the homologous VN GMTs of the IND or 2292B VLP groups, although the IgG1 GMT was lower. In milk, the IgG1 and homologous VN GMTs of the VLP groups were significantly higher than the inactivated IND or the mock-control groups through PPD30. However, the heterologous and homologous VN GMTs of inactivated IND group were statistically similar to the mock-control group at PPD0 and 30, respectively. These results demonstrate that the BRV antibody titers in serum, colostrum and milk are significantly enhanced by the use of triple-layered VLPs and inactivated IND vaccines, but significantly higher antibody responses were observed in the VLP vaccinated cows. The combined IND/2292B VLP vaccine induced comparable VN responses to BRV in serum, colostrum and milk compared to those induced by the individual IND or 2292B VLP vaccines, suggesting that at least two different serotypes can be mixed to confer maximum antibody responses to the incorporated serotypes.

First isolation of rotavirus associated with neonatal diarrhoea in guanacos (Lama guanicoe) in the Argentinean Patagonia region

Group A rotavirus (RV) and coronavirus (CV) are common viral pathogens associated with neonatal diarrhoea in numerous animal species. The purpose of this work was to investigate the presence of these viral agents in two farm populations of captured guanacos (Lama guanicoe) in the Argentinean Patagonia region, that developed severe diarrhoea outbreaks. Stool and serum samples were analysed for RV and bovine CV antigen and antibody enzyme-linked immunosorbent assay. Rotavirus was detected in faeces from two new-born guanacos with acute diarrhoea, one in each farm. After electrophoretic analysis, each isolated strain, showed a distinctive long dsRNA electropherotype characteristic of group A rotaviruses (4:2:3:2). In addition, 95% (38 of 40) of the sampled animals were positive for RV antibodies, suggesting a high prevalence of RV infection in the populations tested. No evidence of CV circulation by antigen or antibody analysis was observed. To our knowledge, this is the first report of the detection and isolation of RV associated with neonatal diarrhoea in Lama guanicoe.

Antigenic and genomic relatedness of turkey-origin coronaviruses, bovine coronaviruses, and infectious bronchitis virus of chickens

In earlier studies in our laboratory, we found that bovine coronavirus (BCV) was pathogenic for 1-day-old turkey poults. This finding prompted us to study the antigenic and genomic relatedness of turkey origin coronaviruses (TOCVs) to BCV. A one-step reverse transcription (RT)-polymerase chain reaction (PCR) targeting a 730-base pair fragment of the nucleocapsid (N) gene of BCV and a nested PCR targeting a 407-base pair fragment of the N gene were used in an attempt to detect TOCV from North Carolina, Indiana, and a prototype turkey coronavirus (TCV) obtained from the American Type Culture Collection. Both the one-step RT-PCR and the nested PCR amplified cell culture-passaged isolates of calf diarrhea strains of BCV but none of the 15 tested TOCVs or transmissible gastroenteritis coronavirus of swine. TOCVs also did not cross-react in a BCV antigen-capture (AC) enzyme-linked immunosorbent assay (ELISA) system with monoclonal antibodies (MAbs) against N, spike glycoprotein, and hemagglutinin esterase glycoprotein proteins of BCV as coating antibodies. The same TOCVs could be detected with primers designed from the genome of infectious bronchitis virus (IBV) of chickens. These primers amplified a 1082-base pair region spanning portions of the membrane glycoprotein (M) and N protein genes of IBV and TCV. The TOCVs also cross-reacted in an AC-ELISA with MAbs against the M and subunit 2 of spike glycoprotein of IBV.

Comparative pathogenesis of tissue culture-adapted and wild-type Cowden porcine enteric calicivirus (PEC) in gnotobiotic pigs and induction of diarrhea by intravenous inoculation of wild-type PEC

Porcine enteric calicivirus (PEC/Cowden) causes diarrhea in pigs, grows in cell culture, and is morphologically and genetically similar to the Sapporo-like human caliciviruses. Genetic analysis revealed that the tissue culture-adapted (TC) Cowden PEC has one distant and three clustered amino acid substitutions in the capsid region and 2 amino acid changes in the RNA polymerase region compared to wild-type (WT) PEC (M. Guo, K.-O. Chang, M. E. Hardy, Q. Zhang, A. V. Parwani, and L. J. Saif, J. Virol. 73:9625-9631, 1999). In this study, the TC PEC, passaged in a porcine kidney cell line, and the WT PEC, passaged in gnotobiotic (Gn) pigs, were used to orally inoculate 13 4- to 6-day-old Gn pigs. No diarrhea developed in the TC-PEC-exposed pigs, whereas moderate diarrhea developed in the WT-PEC orally inoculated pigs, persisting for 2 to 5 days. Fecal virus shedding persisting for at least 7 days was detected by both reverse transcription (RT)-PCR and antigen-enzyme-linked immunosorbent assay (antigen-ELISA) in both TC-PEC and WT-PEC orally inoculated pigs but not in mock-inoculated pigs. The PEC particles were detected by immunoelectron microscopy (IEM) in intestinal contents from all the WT-PEC-inoculated pigs, but not from the TC-PEC-inoculated pigs. Mild (duodenum and jejunum) or no (ileum) villous atrophy was observed in histologic sections of the small intestines of TC-PEC-inoculated pigs, whereas WT PEC caused mild to severe (duodenum and jejunum) villous atrophy and fusion. Scanning electron microscopy confirmed mild shortening and blunting of villi in the duodenum and jejunum of the TC-PEC-inoculated pigs, in contrast to moderate to severe villous shortening and blunting in the duodenum and jejunum of WT-PEC-inoculated pigs. Higher numbers of PEC antigen-positive villous enterocytes were detected by immunofluorescent (IF) staining in the proximal small intestine of the WT-PEC-inoculated pigs, in contrast to low numbers of PEC antigen-positive enterocytes in only one of four TC-PEC-inoculated pigs. No PEC antigen-positive cells were observed in the colon or extraintestinal tissues of all inoculated pigs or in the small intestine of one mock-inoculated pig. Thus, the TC PEC was at least partially attenuated (no diarrhea, mild lesions) after serial passage in cell culture. In further experiments, three 4- to 6-day-old Gn pigs were intravenously (i.v.) inoculated with WT PEC, and all pigs developed diarrhea and villous atrophy in the small intestines resembling that observed in the orally inoculated pigs. Fecal viral shedding persisting for 8 days was detected by both RT-PCR and antigen-ELISA, and PEC was detected by IEM in feces or intestinal contents. The PEC RNA and antigens (at low titers) were detected in acute-phase sera from all the WT-PEC i.v.-inoculated pigs and also from seven of nine of the WT-PEC orally inoculated pigs. Oral or i.v. inoculation of four additional pigs with the PEC-positive acute-phase sera induced diarrhea, small intestinal lesions, PEC shedding in feces, and seroconversion to PEC, confirming the occurrence of viremia during PEC infection, with infectious PEC present in acute-phase sera. No diarrhea, histopathologic changes, or IF staining in the small intestine or fecal or serum detection of PEC was evident in two pigs i.v. mock-inoculated or a pig inoculated i.v. with inactivated WT PEC. To our knowledge, this is the first report of an attenuated enteric calicivirus, the induction of diarrhea, and intestinal lesions in Gn pigs caused by i.v. inoculation of WT PEC and the presence of viremia following PEC infection.

Protective immunity and antibody-secreting cell responses elicited by combined oral attenuated Wa human rotavirus and intranasal Wa 2/6-VLPs with mutant Escherichia coli heat-labile toxin in gnotobiotic pigs

Two combined rotavirus vaccination regimens were evaluated in a gnotobiotic pig model of rotavirus infection and disease and were compared to previously tested rotavirus vaccination regimens. The first (AttHRV/VLP2x) involved oral inoculation with one dose of attenuated (Att) Wa human rotavirus (HRV), followed by two intranasal (i.n.) doses of a rotavirus-like particle (2/6-VLPs) vaccine derived from Wa (VP6) and bovine RF (VP2) rotavirus strains. The 2/6-VLPs were coadministered with a mutant Escherichia coli heat-labile toxin, LT-R192G (mLT) adjuvant. For the second regimen (VLP2x/AttHRV), two i.n. doses of 2/6-VLPs+mLT were given, followed by one oral dose of attenuated Wa HRV. To compare the protective efficacy and immune responses induced by the combined vaccine regimens with individual rotavirus vaccine regimens, we included in the experiments the following vaccine groups: one oral dose of attenuated Wa HRV (AttHRV1x and Mock2x/AttHRV, respectively), three oral doses of attenuated Wa HRV (AttHRV3x), three i.n. doses of 2/6-VLPs plus mLT (VLP3x), three i.n. doses of purified double-layered inactivated Wa HRV plus mLT (InactHRV3x), mLT alone, and mock-inoculated pigs. The isotype, magnitude, and tissue distribution of antibody-secreting cells (ASCs) in the intestinal and systemic lymphoid tissues were evaluated using an enzyme-linked immunospot assay. The AttHRV/VLP2x regimen stimulated the highest mean numbers of intestinal immunoglobulin A (IgA) ASCs prechallenge among all vaccine groups. This regimen induced partial protection against virus shedding (58%) and diarrhea (44%) upon challenge of pigs with virulent Wa HRV. The reverse VLP2x/AttHRV regimen was less efficacious than the AttHRV/VLP2x regimen in inducing IgA ASC responses and protection against diarrhea (25% protection rate) but was more efficacious than VLP3x or InactHRV3x (no protection). In conclusion, the AttHRV/VLP2x vaccination regimen stimulated the strongest B-cell responses in the intestinal mucosal immune system at challenge and conferred a moderately high protection rate against rotavirus disease, indicating that priming of the mucosal inductive site at the portal of natural infection with a replicating vaccine, followed by boosting with a nonreplicating vaccine at a second mucosal inductive site, may be a highly effective approach to stimulate the mucosal immune system and induce protective immunity against various mucosal pathogens.

Evaluation of concurrent shedding of bovine coronavirus via the respiratory tract and enteric route in feedlot cattle

OBJECTIVE

To assess the relationship between shedding of bovine coronavirus (BCV) via the respiratory tract and enteric routes and the association with weight gain in feedlot cattle.

ANIMALS

56 crossbred steers.

PROCEDURES

Paired fecal samples and nasal swab specimens were obtained and were tested for BCV, using antigen-capture ELISA. Paired serum samples obtained were tested for antibodies to BCV, using antibody-detection ELISA. Information was collected on weight gain, clinical signs, and treatments for enteric and respiratory tract disease during the study period.

RESULTS

Number of samples positive for bovine respiratory coronavirus (BRCV) or bovine enteric coro navirus (BECV) was 37/224 (17%) and 48/223 (22%), respectively. Some cattle (25/46, 45%) shed BECV and BRCV. There were 25/29 (86%) cattle positive for BECV that shed BRCV, but only 1/27 (4%) cattle negative to BECV shed BRCV. Twenty-seven of 48 (56%) paired nasal swab specimens and fecal samples positive for BECV were positive for BRCV. In contrast, only 10/175 (6%) paired nasal swab specimens and fecal samples negative for BECV were positive for BRCV. Only shedding of BECV was associated with significantly reduced weight gain. Seroconversion to BCV during the 21 days after arrival was detected in 95% of the cattle tested.

CONCLUSIONS AND CLINICAL IMPLICATIONS

Feedlot cattle infected with BCV after transport shed BCV from the respiratory tract and in the feces. Fecal shedding of BCV was associated with significantly reduced weight gain. Developing appropriate control measures for BCV infections could help reduce the decreased weight gain observed among infected feedlot cattle.

Antibody-secreting cell responses to rotavirus proteins in gnotobiotic pigs inoculated with attenuated or virulent human rotavirus

Because of their similarities to infants in mucosal immune responses and their susceptibility to human rotavirus (HRV) diarrhea, gnotobiotic pigs provide a useful model for rotaviral disease. In this study, we performed quantitative enzyme-linked immunospot (ELISPOT) assays to measure local and systemic isotype-specific antibody-secreting cell (ASC) responses to individual structural (VP4, VP6, and VP7) and nonstructural (NSP3 and NSP4) proteins of Wa HRV. The Spodoptera frugiperda cells expressing each recombinant baculovirus HRV protein were formalin fixed and used as antigen for ELISPOT assays. Neonatal gnotobiotic pigs were orally inoculated once with virulent Wa (WaV) or three times with attenuated Wa (WaA) HRV or mock inoculated (Mock) and then were challenged with virulent Wa (WaV/PC) 28 days after the first inoculation. The ASCs from intestinal and systemic lymphoid tissues of pigs from each group were quantitated by ELISPOT assay at the day of challenge, at postinoculation day 28 (WaV, WaA, and Mock) or at postchallenge day (PCD) 7 (WaV+WaV/PC, WaA+WaV/PC, and Mock+WaV/PC). In all virus-inoculated pigs, regardless of the inoculum, lymphoid tissue, or isotype, VP6 induced the highest numbers of ASCs, followed by VP4; ASCs specific for VP7, NSP3, and NSP4 were less numerous. At challenge, total HRV- and HRV protein-specific immunoglobulin A (IgA) and IgG ASCs in intestinal lymphoid tissues were significantly greater in WaV- than in WaA-inoculated pigs, and WaV pigs were fully protected against diarrhea postchallenge, whereas the WaA pigs were partially protected. At PCD 7, there were no significant differences in ASC numbers for any HRV proteins between the WaV+WaV/PC and WaA+WaV/PC groups.

Short-term immunoglobulin A B-cell memory resides in intestinal lymphoid tissues but not in bone marrow of gnotobiotic pigs inoculated with Wa human rotavirus

Immunological memory is important for protecting the host from reinfection. To investigate the development and sites of residence of intestinal memory B cells, and their role in protective immunity to reinfection with an enteric virus, we assessed the association between memory B cell and antibody-secreting cell (ASC) responses and protection using a gnotobiotic pig model for human rotavirus (HRV) infection and diarrhoea. The isotypes, quantities and tissue distribution of rotavirus-specific memory B cells and ASC were evaluated prechallenge (28 and 83 postinoculation days [PID]) and postchallenge (7 postchallenge days [PCD]), using enzyme-linked immunospot (ELISPOT) assay, in gnotobiotic pigs inoculated once with virulent or three times with attenuated HRV and challenged at PID 28 with the corresponding virulent HRV. Complete protection against HRV shedding and diarrhoea was associated with significantly higher numbers of immunoglobulin A (IgA) and immunoglobulin G (IgG) memory B cells and ASC in the ileum of virulent HRV-inoculated pigs at challenge. In contrast, pigs inoculated with attenuated HRV had lower numbers of IgA and IgG memory B cells and ASC in intestinal lymphoid tissues, but higher numbers in the spleen. The bone marrow had the lowest mean numbers of IgA and IgG memory B cells and ASC prechallenge in both groups of HRV-inoculated pigs. Therefore, bone marrow was not a site for IgA and IgG rotavirus-specific antibody production or for memory B cells after inoculation with live rotavirus, from 28 PID up to at least 83 PID. The effect of in vitro antigen dose was examined and it was determined to play an important role in the development of ASC from memory B cells for the different tissues examined.

Immune responses and protection obtained with rotavirus VP6 DNA vaccines given by intramuscular injection

Intramuscular (i.m.) injection of murine VP6 DNA vaccines raised high titers of rotavirus-specific serum IgG and IgA antibodies in BALB/c mice. A Th1-like antibody response was generated based on the ratio of serum IgG2a to IgG1 antibodies. Rotavirus-specific serum IgA but not fecal IgA was detected in mice prior to rotavirus challenge. Partial protection against rotavirus challenge was achieved as measured by reduction of rotavirus antigen shedding in feces. A similar level of protection was found with a bovine rotavirus VP6 DNA vaccine against a murine rotavirus challenge, suggesting that heterologous protection can be obtained by immunizing with VP6 DNA vaccines. We did not directly test for cytotoxic T lymphocyte (CTL) activity, but in vivo depletion of CD8+ T cells in mice immunized with a murine VP6 DNA vaccine did not significantly change the duration of virus shedding or the pattern of protection obtained. This finding suggested that CD8+ CTL activity was not essential for the partial protection we obtained by i.m. immunization of mice with VP6 DNA vaccines.

Expression and self-assembly in baculovirus of porcine enteric calicivirus capsids into virus-like particles and their use in an enzyme-linked immunosorbent assay for antibody detection in swine

Porcine enteric calicivirus (PEC) causes diarrhea and intestinal lesions in pigs. PEC strain Cowden grows to low to moderate titers in cell culture but only with the addition of intestinal contents from uninfected gnotobiotic pigs (W. T. Flynn and L. J. Saif, J. Clin. Microbiol. 26:206--212, 1988; A. V. Parwani, W. T. Flynn, K. L. Gadfield, and L. J. Saif, Arch. Virol. 120:115--122, 1991). Cloning and sequence analysis of the PEC Cowden full-length genome revealed that it is most closely related genetically to the human Sapporo-like viruses. In this study, the complete PEC capsid gene was subcloned into the plasmid pBlueBac4.5 and the recombinant baculoviruses were identified by plaque assay and PCR. The PEC capsid protein was expressed in insect (Sf9) cells inoculated with the recombinant baculoviruses, and the recombinant capsid proteins self- assembled into virus-like particles (VLPs) that were released into the cell supernatant and purified by CsCl gradient centrifugation. The PEC VLPs had the same molecular mass (58 kDa) as the native virus capsid and reacted with pig hyperimmune and convalescent-phase sera to PEC Cowden in enzyme-linked immunosorbent assay (ELISA) and Western blotting. The PEC capsid VLPs were morphologically and antigenically similar to the native virus by immune electron microscopy. High titers (1:102,400 to 204,800) of PEC-specific antibodies were induced in guinea pigs inoculated with PEC VLPs, suggesting that the VLPs could be useful for future candidate PEC vaccines. A fixed-cell ELISA and VLP ELISA were developed to detect PEC serum antibodies in pigs. For the fixed-cell ELISA, Sf9 cells were infected with recombinant baculoviruses expressing PEC capsids, followed by cell fixation with formalin. For the VLP ELISA, the VLPs were used for the coating antigen. Our data indicate that both tests were rapid, specific, and reproducible and might be used for large-scale serological investigations of PEC antibodies in swine.

Completion of the four large gene sequences of porcine group C Cowden rotavirus

The terminal nucleotide sequences of group C Cowden rotavirus gene segments 1-4 were determined. When compared with the published sequences, we found 14 to 29 additional nt at the 5' ends of the four reported gene sequences. For the 3' ends, we observed an additional 16 nt in gene 2 and 14 fewer nt in gene 4.

Experimental bovine coronavirus in turkey poults and young chickens

The DB2 calf strain of bovine coronavirus (BCV) was used to inoculate 1-day-old specific-pathogen-free (SPF) turkey poults in three trials. In all trials, the birds developed clinical signs of enteritis at 48-72 hr postinoculation. Birds euthanatized at 3, 5, and 7 days postinoculation (DPI) had flaccid, pale intestines with watery contents, and the ceca were markedly enlarged with frothy contents. Coronavirus particles were detected by immune electron microscopy with BCV antibodies from the intestinal contents of birds killed at 3, 5, 7, and 12 DPI. Body weights of inoculated poults killed at 3, 5, and 7 DPI were significantly reduced as compared with controls. Hemagglutinating antibodies were detected in sera of convalescent birds at 12 DPI. However, experimental inoculation of 1-day-old SPF chicks in two trials with the same virus resulted in no clinical signs or macroscopic or microscopic lesions. No coronaviruses were detected from intestinal contents, and there were no significant differences in body weights of inoculated and noninoculated control chicks.

Detection and molecular characterization of cultivable caliciviruses from clinically normal mink and enteric caliciviruses associated with diarrhea in mink

Enteric caliciviruses are emerging pathogens responsible for diarrhea or gastroenteritis in their respective hosts. In this report, mink enteric caliciviruses (MEC) were detected in feces from diarrheic mink by both immune electron microscopy (IEM) and RT-PCR using a broadly reactive primer pair (p289/290) targeting the highly conserved RNA polymerase regions of the enteric caliciviruses, Norwalk-like viruses (NLVs) and Sapporo-like viruses (SLVs). The MEC possess classical caliciviral morphology with typical cup-shaped depressions on the viral surface. Sequence analyses based on nucleotide and predicted amino acid (aa) sequences of the RT-PCR products indicated that MEC is most closely related genetically to SLVs of humans and animals. The MEC shared the highest aa identities (64-71%) in the RNA polymerase region with both human SLVs and the porcine enteric calicivirus (PEC) Cowden strain SLV, indicating that MEC may belong to an individual genogroup or subgroup in the SLV genus. The MEC shared only limited aa identities in the RNA polymerase region with vesiviruses (40-51%) and NLVs (29-33%). The RNA polymerase regions of the cultivable, non-enteric mink caliciviruses (MCV) were also amplified by RT-PCR using the primer pair Pol1/Pol3 based on sequences of vesiviruses, and the primer pair p289/290. Sequence analysis indicated that these MCV shared higher aa identities in the RNA polymerase region with vesiviruses (58-81%) than with SLVs (43-51%) including the MEC, lagoviruses (35-37%) and NLVs (27-35%), suggesting that they are most closely related genetically to vesiviruses. The MEC associated with diarrhea in mink are morphologically similar to but are genetically distinct from the cultivable MCV and likely represent a new member of the SLV genus.

Cross-protection studies between respiratory and calf diarrhea and winter dysentery coronavirus strains in calves and RT-PCR and nested PCR for their detection

A 1-step RT-PCR assay, targeting a 730 bp fragment of the nucleocapsid (N) gene of bovine coronavirus (BCV), and a nested PCR assay, targeting a 407 bp fragment of the N gene, were developed to detect BCV in nasal swab and fecal samples of calves experimentally exposed to BCV. Both 1-step RT-PCR and nested PCR recognized cell culture passaged isolates of 10 bovine respiratory coronavirus (BRCV), 5 calf diarrhea (CD) and 8 winter dysentery (WD) strains of BCV, but not transmissible gastroenteritis coronavirus or bovine rotavirus. The sensitivity of the 1-step RT-PCR and nested PCR was compared to that of an antigen-capture ELISA. The lowest detection limit of the 1-step RT-PCR and nested PCR as determined by using tenfold serial dilutions of the BRCV 255 and 440 strains in BCV negative nasal swab suspensions from preexposure gnotobiotic calves was 2 x 10(4) and 2 x 10(2) TCID50/0.1 ml for each strain, respectively. The lowest detection limit of the antigen-capture ELISA as determined by using the same serially diluted samples was 1 x 10(6) TCID50/0.1 ml for each strain. Therefore, the 1-step RT-PCR and nested PCR assays were 50 and 5000 times, respectively more sensitive than the antigen-capture ELISA to detect BRCV in nasal swab suspensions. To investigate in vivo cross-protection between the BRCV and CD or WD strains of BCV and to detect nasal and fecal shedding of BCV using the 1-step RT-PCR, nested PCR and antigen-capture ELISA, 6 colostrum-deprived and two gnotobiotic calves were inoculated with a BRCV, a CD or a WD strain of BCV and then challenged 3-4 weeks later with either BRCV, CD or WD strains of BCV. All calves developed diarrhea after inoculation and BCV antigen (ELISA) or RNA (RT-PCR) was detected in the diarrheic fecal samples or the corresponding nasal swab samples. In addition, low amounts of BCV were also detected only by nested PCR in the fecal and nasal swab samples before and after diarrhea. No respiratory clinical signs were observed during the entire experimental period, but elevated rectal temperatures were detected during diarrhea in the BCV-inoculated calves. All calves recovered from infection with the BRCV, CD, or WD strains of BCV were protected from BCV-associated diarrhea after challenge exposure with either a heterologous or homologous strain of BCV. However, all calves challenged with heterologous BCV strains showed subclinical BCV infection evident by detection of nasal and fecal shedding of BCV RNA detected only by nested PCR. Such results confirm field and experimental data documenting reinfection of the respiratory and enteric tracts of cattle, suggesting that, in closed herds, respiratory or enteric tract reinfections may constitute a source of BCV transmissible to cows (WD) or neonatal or feedlot calves. In addition, the present 1-step RT-PCR and nested PCR assays were highly sensitive to detect BCV in nasal swab and fecal specimens. Therefore, these assays should be useful to diagnose BCV infections in calves and adult cows.

Detection and isolation of coronavirus from feces of three herds of feedlot cattle during outbreaks of winter dysentery-like disease

Clinical signs of a winter dysentery-like syndrome in 6- to 9-month-old cattle in 3 feedlots included acute onset of diarrhea with high morbidity and low mortality, respiratory tract problems that included dyspnea, coughing, and nasal discharge, and high rectal temperatures. Bovine coronavirus was detected by use of an ELISA and immune electron microscopy in fecal and nasal swab samples and by immunohistochemical analysis of intestinal sections collected from calves during necropsy. Bovine coronavirus should be considered in the differential diagnoses for diseases that cause acute onset of bloody diarrhea in feedlot cattle.

Intranasal administration of 2/6-rotavirus-like particles with mutant Escherichia coli heat-labile toxin (LT-R192G) induces antibody-secreting cell responses but not protective immunity in gnotobiotic pigs

We investigated the immunogenicity of recombinant double-layered rotavirus-like particle (2/6-VLPs) vaccines derived from simian SA11 or human (VP6) Wa and bovine RF (VP2) rotavirus strains. The 2/6-VLPs were administered to gnotobiotic pigs intranasally (i.n.) with a mutant Escherichia coli heat-labile toxin, LT-R192G (mLT), as mucosal adjuvant. Pigs were challenged with virulent Wa (P1A[8],G1) human rotavirus at postinoculation day (PID) 21 (two-dose VLP regimen) or 28 (three-dose VLP regimen). In vivo antigen-activated antibody-secreting cells (ASC) (effector B cells) and in vitro antigen-reactivated ASC (derived from memory B cells) from intestinal and systemic lymphoid tissues (duodenum, ileum, mesenteric lymph nodes [MLN], spleen, peripheral blood lymphocytes [PBL], and bone marrow lymphocytes) collected at selected times were quantitated by enzyme-linked immunospot assays. Rotavirus-specific immunoglobulin M (IgM), IgA, and IgG ASC and memory B-cell responses were detected by PID 21 or 28 in intestinal and systemic lymphoid tissues after i.n. inoculation with two or three doses of 2/6-VLPs with or without mLT. Greater mean numbers of virus-specific ASC and memory B cells in all tissues prechallenge were induced in pigs inoculated with two doses of SA11 2/6-VLPs plus mLT compared to SA11 2/6-VLPs without mLT. After challenge, anamnestic IgA and IgG ASC and memory B-cell responses were detected in intestinal lymphoid tissues of all VLP-inoculated groups, but serum virus-neutralizing antibody titers were not significantly enhanced compared to the challenged controls. Pigs inoculated with Wa-RF 2/6-VLPs (with or without mLT) developed higher anamnestic IgA and IgG ASC responses in ileum after challenge compared to pigs inoculated with SA11 2/6-VLPs (with or without mLT). Three doses of SA 11 2/6-VLP plus mLT induced the highest mean numbers of IgG memory B cells in MLN, spleen, and PBL among all groups postchallenge. However, no significant protection against diarrhea or virus shedding was evident in any of the 2/6-VLP (with or without mLT)-inoculated pigs after challenge with virulent Wa human rotavirus. These results indicate that 2/6-VLP vaccines are immunogenic in gnotobiotic pigs when inoculated i.n. and that the adjuvant mLT enhanced their immunogenicity. However, i.n. inoculation of gnotobiotic pigs with 2/6-VLPs did not confer protection against human rotavirus challenge.

Association between infection of the respiratory tract attributable to bovine coronavirus and health and growth performance of cattle in feedlots

OBJECTIVE

To determine the association between respiratory tract infection with bovine coronavirus (BCV), treatment for respiratory tract disease, pulmonary lesions at slaughter, and average daily gain in cattle in feedlots.

ANIMALS

837 calves in feedlots in Ohio and Texas.

PROCEDURE

Nasal swab specimens were obtained from cattle at arrival in a feedlot (day 0) and at various times during the initial 28 days after arrival. Specimens were tested for BCV, using an antigen-capture ELISA. Serum samples were obtained at arrival and again 28 days after arrival and tested for antibodies to BCV, using an antibody-detection ELISA. Information was collected regarding treatment for cattle with respiratory tract disease and average daily gain during the feeding period. Pulmonary lesions were evaluated at slaughter.

RESULTS

Cattle shedding BCV from the nasal cavity and developing an antibody response against BCV were 1.6 times more likely to require treatment for respiratory tract disease than cattle that did not shed the virus or develop an immune response against BCV. Additionally, cattle that shed BCV from the nasal cavity were 2.2 times more likely to have pulmonary lesions at slaughter than cattle that did not shed the virus. The BCV shedding or seroconversion status did not affect average daily gain.

CONCLUSIONS AND CLINICAL RELEVANCE

Bovine coronavirus infects feedlot cattle and is associated with an increased risk for cattle developing respiratory tract disease and pulmonary lesions. Development of appropriate control measures could help reduce the incidence of respiratory tract disease.

Antibody titers against bovine coronavirus and shedding of the virus via the respiratory tract in feedlot cattle

OBJECTIVE

To describe patterns of seroconversion to bovine coronavirus (BCV) and shedding of BCV from the respiratory tract in feedlot cattle.

ANIMALS

1,074 calves in feedlots in Ohio, Texas, and Nebraska.

PROCEDURE

Nasal swab specimens were obtained at time of arrival (day 0) and at various times during the initial 28 days after arrival at feedlots. Specimens were tested for BCV, using an antigen-capture ELISA. Serum samples were obtained at time of arrival and again 28 days after arrival; sera were analyzed for antibodies to BCV, using an antibody-detection ELISA.

RESULTS

Samples from 12 groups of cattle entering 7 feedlots during a 3-year period revealed that 78 of 1,074 (7.3%) cattle were shedding BCV (range, 0 to 35.9% within specific groups). At time of arrival, 508 of 814 (62.4%) cattle had low (< 50) or undetectable BCV antibody titers. Seroconversion to BCV during the initial 28 days after arrival was detected in 473 of 814 (58%) cattle tested (range, 20.3 to 84.1 % within specific groups). In cattle shedding BCV from the nasal passages, 49 of 68 (72.1 %) seroconverted, and 472 of 746 (63.3%) cattle that were not shedding the virus seroconverted.

CONCLUSIONS AND CLINICAL RELEVANCE

Bovine coronavirus can be detected in populations of feedlot cattle in the form of viral shedding as well as seroconversion to the virus. Although only a few cattle were shedding the virus at the time of arrival at a feedlot, most of the cattle seroconverted to BCV by 28 days after arrival.

Comparative sequence analysis of the VP7 genes of G6, G8 and G10 bovine group A rotarviruses and further characterization of G6 subtypes

We previously reported the relatively high prevalence (15%) of bovine G6 subtypes (G6s) in the field using RT-PCR and restriction fragment length polymorphism (RFLP) analysis (Chang et al., Arch. Virol. 141: 1727-39). In the present study, we report the nucleotide and antigenic characterization of a G6s strain (C-8336). We also sequenced the VP7 genes of four additional bovine rotavirus (BRV) strains: another G6s (MC27), G6 (IND), G8 (C-8008) and G10 (2292B) and compared these with other bovine and human rotavirus strains. The C-8336 and MC27 strains were confirmed as P[11]G6s by RT-PCR and RFLP analysis. The VP7 genes of the C-8336 and MC27 strains showed high homology to each other (approximately 98%) and with other bovine G6s strains (greater than 95% homology in nucleotide and amino acid sequence with KN-4[P[11]G6s]) and also showed lower, but substantial sequence homology with human G6s strains and prototype G6 BRV (79-87% in nucleotide and 88-91% in amino acid). Serologic analysis of the cell culture adapted C-8336 strain showed that it was neutralized by a G6 monoclonal antibody (MAb IC3) to similar titers as the reference NCDV and IND G6 strains. In two-way cross-neutralization tests, strain C-8336 showed 4- to 16-fold differences in antibody titers with NCDV and IND G6 BRV. Moreover polyclonal antiserum against strain C-8336 neutralized the NCDV and IND strains weakly. Genetic variability was also observed among G8 and G10 bovine and human group A rotaviruses: the VP7 genes of the bovine C-8008 (P[5]G8) and 2292 B (P[11]G10) strains showed from 10 to 17% nucleotide divergence with those of Cody 1801 (P[1]G8, bovine), A5 (P[1]G8, bovine), 69M (P[10]G8, human) and Hal 1166 (P[14]G8, human), and I321(P[11]G10, human) and MC35 (P[14]G10, human) rotaviruses, respectively. The divergence of VP7 genes among bovine and human G6, G8 and G10 strains appears related to host species origin and their combination with VP4 (P type). The data presented in this report confirms the genetic variability among homotypic bovine and human strains and highlights the importance of continued monitoring of BRV G and P types circulating in the field for the future development and monitoring of effective vaccines.

Development of a reverse transcription-nested polymerase chain reaction assay for differential diagnosis of transmissible gastroenteritis virus and porcine respiratory coronavirus from feces and nasal swabs of infected pigs

Transmissible gastroenteritis virus (TGEV), a coronavirus, replicates in intestinal enterocytes and causes diarrhea in young pigs. Porcine respiratory coronavirus (PRCV), a spike (S) gene natural deletion mutant of TGEV, has a respiratory tissue tropism and causes mild or subclinical respiratory infections. Conventional antigen-based diagnostic tests fail to differentiate TGEV and PRCV, and a blocking ELISA test to serologically differentiate TGEV/PRCV-infected pigs is conducted on convalescent serum retrospectively after disease outbreaks. A reverse transcription (RT)-nested polymerase chain reaction (PCR) with primers targeted to the S gene deletion region to differentiate TGEV/PRCV was developed. The specificity of the RT-nested PCR was confirmed with reference and recent field strains of TGEV/PRCV, and its sensitivity was analyzed by testing nasal and fecal samples collected from pigs at various days postinoculation (DPI) with TGEV or PRCV. Specific PCR products for TGEV/PRCV were detected only with the homologous reference or field coronaviruses and for 10-14 DPI of pigs with TGEV (feces) or PRCV (nasal samples). The RT-nested PCR assay was more sensitive than antigen-based assays on the basis of duration of virus detection in experimentally infected pigs and was directly applicable to nasal as well as fecal specimens from the field.

Comparative pathogenesis of enteric viral infections of swine

At least 11 enteric viruses belonging to 6 distinct families (Adenoviridae, Astroviridae, Caliciviridae, Coronaviridae, Parvoviridae, and Reoviridae) cause diarrhea in swine mainly during the nursing and immediate post-weaning period. Most infect the small intestinal enterocytes, inducing various degrees of villous atrophy and subsequently a malabsorptive, maldigestive diarrhea. In addition rotaviruses possess an enterotoxin (NSP4) which induces a secretory diarrhea in mice. These viruses have distinct predilections for different vertical (villus/crypt) and horizontal (duodenum, jejunum, ileum, colon) replication sites in the intestine and the diarrhea intensity is often related to the extent of viral replication at these sites. In addition concurrent infections with multiple enteric viruses can produce synergistic or additive effects leading to more extensive villous atrophy throughout the intestine and more severe and prolonged diarrhea. Knowledge of enteric viral replication sites and comparative mechanisms of diarrhea induction may lead to new or improved vaccine strategies or therapeutic approaches for the prevention or treatment of these viral diarrheas.

Molecular characterization and pathogenesis of transmissible gastroenteritis coronavirus (TGEV) and porcine respiratory coronavirus (PRCV) field isolates co-circulating in a swine herd

TGEV replicates in intestinal enterocytes and causes diarrhea in young pigs. PRCV, a spike (S) gene deletion mutant of TGEV with an altered respiratory tissue tropism, causes mild or subclinical respiratory infections. Comparisons of TGEV and PRCV strains suggest that tropism and pathogenicity are influenced by the S gene and ORF3, respectively. Recently, outbreaks of TGE of reduced virulence were reported in the field. We investigated a similar suspect TGEV outbreak of reduced virulence in nursery pigs from a swine herd in the Midwest. A TGEV strain (BW021898B) was isolated in swine testicular cells from gut contents of a diarrheic pig and three PRCV strains (BW126, BW154, BW155) were isolated from nasal swabs from normal TGEV-seronegative sentinel pigs in contact with the diarrheic pigs. Sequence analysis of the TGEV isolate in the partial S gene and ORF3/3a and ORF3-1/3b revealed high homology with enteropathogenic TGEV strains. Gnotobiotic pig inoculation and histopathological results revealed that this TGEV isolate retained virulence even though in the field outbreak the diarrheal disease was of reduced severity. Sequence analysis of the S gene deletion region of the three PRCV isolates revealed identical deletions between nt 105-752, which differ from deletions previously reported among PRCV strains. The three PRCV isolates had variable sequence changes in ORF 3/3a and ORF 3-1/3b, affecting the ORF size and amino acid sequence. Thus, sequence analysis and pathogenicity studies indicate that this TGEV isolate resembles other enteropathogenic TGEV strains. Therefore, the reduced severity of TGE observed in this herd may be due to the ongoing PRCV infections, which induce antibodies cross-reactive with TGEV and result in decreased disease severity. The results outlined in this study highlight the need to monitor the molecular epidemiology of TGEV/PRCV strains with sensitive differential diagnostic assays, followed by sequence analysis of the critical regions to identify changes and pathogenicity studies to confirm the disease potential of the TGEV isolates.

Molecular characterization of a porcine enteric calicivirus genetically related to Sapporo-like human caliciviruses

Porcine enteric calicivirus (PEC) is associated with diarrhea in pigs, and to date it is the only cultivable enteric calicivirus (tissue culture-adapted [TC] PEC/Cowden). Based on sequence analysis of cDNA clones and reverse transcription-PCR products, TC PEC/Cowden has an RNA genome of 7,320 bp, excluding its 3' poly(A)(+) tail. The genome is organized in two open reading frames (ORFs), similar to the organizations of the human Sapporo-like viruses (SLVs) and the lagoviruses. ORF1 encodes the polyprotein that is fused to and contiguous with the capsid protein. ORF2 at the 3' end encodes a small basic protein of 164 amino acids. Among caliciviruses, PEC has the highest amino acid sequence identities in the putative RNA polymerase (66%), 2C helicase (49.6%), 3C-like protease (43.7%), and capsid (39%) regions with the SLVs, indicating that PEC is genetically most closely related to the SLVs. The complete RNA genome of wild-type (WT) PEC/Cowden was also sequenced. Sequence comparisons revealed that the WT and TC PEC/Cowden have 100% nucleotide sequence identities in the 5' terminus, 2C helicase, ORF2, and the 3' nontranslated region. TC PEC/Cowden has one silent mutation in its protease, two amino acid changes and a silent mutation in its RNA polymerase, and five nucleotide substitutions in its capsid that result in one distant and three clustered amino acid changes and a silent mutation. These substitutions may be associated with adaptation of TC PEC/Cowden to cell culture. The cultivable PEC should be a useful model for studies of the pathogenesis, replication, and possible rescue of uncultivable human enteric caliciviruses.

Dual infection of gnotobiotic calves with bovine strains of group A and porcine-like group C rotaviruses influences pathogenesis of the group C rotavirus

There is serological evidence that bovine group C rotaviruses exist in the United States, but there are no reports of their isolation. Ninety fecal samples from calves with diarrhea, 81 samples from adult cows with diarrhea (winter dysentery), and 20 fecal samples from healthy adult cows were tested for group C rotaviruses by polyacrylamide gel electrophoresis, immune electron microscopy, and reverse transcription-PCR (RT-PCR). Three samples from adult cow diarrhea cases were positive only by RT-PCR, and a group C rotavirus was isolated from a positive sample in monkey kidney (MA104) cells (WD534tc/C). Genetically and serologically, the WD534tc/C strain was more closely related to the Cowden porcine group C strain than to the Shintoku bovine strain. Because the original cow feces also contained a group A rotavirus (detected after passage in cell culture), we hypothesized that such dual-rotavirus infections might play a role in the pathogenesis and host adaptation of rotaviruses. Thus, we examined the pathogenesis of WD534tc/C alone or combined with virulent (IND/A) or attenuated (NCDV/A) bovine group A rotaviruses in gnotobiotic calves. WD534tc/C alone induced diarrhea without (or with limited) virus shedding in inoculated calves (n = 3). In contrast, all calves coinfected with WD534tc/C and IND/A (n = 2) developed diarrhea and shed both viruses, whereas calves coinfected with WD534tc/C and NCDV/A (n = 3) developed diarrhea but did not shed either virus. Infection with WD534tc/C or NCDV/A alone caused only mild villous atrophy (jejunum and/or ileum), whereas dual infection with both viruses induced lesions throughout the small intestine. Although IND/A alone caused villous atrophy, more-widespread small intestinal lesions occurred in calves coinfected with WD534tc/C and IND/A. In conclusion, coinfection of calves with group A rotaviruses enhanced fecal shedding of a bovine group C rotavirus and the extent of histopathological lesions in the small intestines. Thus, our findings suggest a potential novel hypothesis involving dual infections for the adaptation of heterologous rotaviruses to new host species.

Isolation of bovine respiratory coronaviruses from feedlot cattle and comparison of their biological and antigenic properties with bovine enteric coronaviruses

OBJECTIVE

To isolate bovine coronaviruses from the respiratory tracts of feedlot cattle and compare antigenic and biological properties of these strains with bovine enteric coronaviruses.

ANIMALS

5- to 8-month-old mixed-breed cattle at 4 feedlots.

PROCEDURE

Samples were obtained from the nasal passages for testing. The 13 samples with the highest magnitude of positive values for bovine coronavirus (BCV) were cultured. Ten strains of bovine respiratory coronavirus (BRCV) were adapted successfully to serial passage. After observation of cytopathic effects (CPE) and confirmation of BRCV by immune electron microscopy and immunofluorescence testing, cell culture-adapted strains were cloned by limiting dilution. These isolates then were compared with a panel of bovine enteric coronaviruses (BECV), using hemagglutination (HA), receptor-destroying enzyme activity (RDE), hemagglutination inhibition (HI), and virus neutralization (VN) assays. Antigenic relatedness values then were calculated.

RESULTS

The BRCV were detected in 105 of 488 (21.5%) of the cattle tested. Of 13 strains tested, 10 were isolated in cell culture. Six of the BRCV strains were similar to 2 strains obtained from neonatal calves with diarrhea and 2 strains from adult cattle with winter dysentery. The other 4 BRCV isolates had high RDE activity against mouse erythrocytes but differed from other strains of BECV Nine of 10 BRCV isolates had properties similar to the 2 BECV subtypes.

CONCLUSIONS AND CLINICAL RELEVANCE

The BRCV can be isolated from nasal passages of cattle entering feedlots. Most BRCV were similar to BECV strains, although a few had unique properties. Vaccines developed to protect against enteric strains also may protect against respiratory tract strains.