Development and application of one-step multiplex Real-Time PCR for detection of three main pathogens associated with bovine neonatal diarrhea

Introduction

Neonatal calf diarrhea (NCD) is one of the most common diseases in calves, causing huge economic and productivity losses to the bovine industry worldwide. The main pathogens include bovine rotavirus (BRV), bovine coronavirus (BCoV), and Enterotoxigenic Escherichia coli (ETEC) K99. Since multiple infectious agents can be involved in calf diarrhea, detecting each causative agent by traditional methods is laborious and expensive.

Methods

In this study, we developed a one-step multiplex Real-Time PCR assay to simultaneously detect BRV, BCoV, and E. coli K99+. The assay performance on field samples was evaluated on 1100 rectal swabs of diseased cattle with diarrhea symptoms and compared with the conventional gel-based RT-PCR assay detect BRV, BCoV, and E. coli K99+.

Results

The established assay could specifically detect the target pathogens without cross-reactivity with other pathogens. A single real-time PCR can detect ~1 copy/µL for each pathogen, and multiplex real-time PCR has a detection limit of 10 copies/µL. Reproducibility as measured by standard deviation and coefficient of variation were desirable. The triple real-time PCR method established in this study was compared with gel-based PT-PCR. Both methods are reasonably consistent, while the real-time PCR assay was more sensitive and could rapidly distinguish these three pathogens in one tube. Analysis of surveillance data showed that BRV and BCoV are major enteric viral pathogens accounting for calves' diarrhea in China.

Discussion

The established assay has excellent specificity and sensitivity and was suitable for clinical application. The robustness and high-throughput performance of the developed assay make it a powerful tool in diagnostic applications and calf diarrhea research. ​.

Use of live attenuated recombinant Newcastle disease virus carrying avian paramyxovirus 2 HN and F protein genes to enhance immune responses against species A rotavirus VP6 protein

Numerous infectious diseases in cattle lead to reductions in body weight, milk production, and reproductive performance. Cattle are primarily vaccinated using inactivated vaccines due to their increased safety. However, inactivated vaccines generally result in weaker immunity compared with live attenuated vaccines, which may be insufficient in certain cases. Over the last few decades, there has been extensive research on the use of the Newcastle disease virus (NDV) as a live vaccine vector for economically significant livestock diseases. A single vaccination dose of NDV can sufficiently induce immunity; therefore, a booster vaccination dose is expected to yield limited induction of further immune response. We previously developed recombinant chimeric NDV (rNDV-2F2HN), in which its hemagglutinin-neuraminidase (HN) and fusion (F) proteins were replaced with those of avian paramyxovirus 2 (APMV-2). In vitro analysis revealed that rNDV-2F2HN expressing human interferon-gamma had potential as a cancer therapeutic tool, particularly for immunized individuals. In the present study, we constructed rNDV-2F2HN expressing the bovine rotavirus antigen VP6 (rNDV-2F2HN-VP6) and evaluated its immune response in mice previously immunized with NDV. Mice primarily inoculated with recombinant wild-type NDV expressing VP6 (rNDV-WT-VP6), followed by a booster inoculation of rNDV-2F2HN-VP6, showed a significantly stronger immune response than that in mice that received rNDV-WT-VP6 as both primary and booster inoculations. Therefore, our findings suggest that robust immunity could be obtained from the effects of chimeric rNDV-2F2HN expressing the same or a different antigen of a particular pathogen as a live attenuated vaccine vector.

Establishment of an Indirect ELISA Method for the Detection of the Bovine Rotavirus VP6 Protein

The objective of this study was to develop an indirect ELISA utilizing a polyclonal antibody against bovine rotavirus (BRV) VP6 protein. To achieve this, pcDNA3.1-VP6, a recombinant eukaryotic expression plasmid, was constructed based on the sequence of the conserved BRV gene VP6 and was transfected into CHO-K1 cells using the transient transfection method. The VP6 protein was purified as the coating antigen using nickel ion affinity chromatography, and an indirect ELISA was subsequently established. The study found that the optimal concentration of coating for the VP6 protein was 1 μg/mL. The optimal blocking solution was 3% skim milk, and the blocking time was 120 min. The secondary antibody was diluted to 1:4000, and the incubation time for the secondary antibody was 30 min. A positive result was indicated when the serum OD450 was greater than or equal to 0.357. The coefficients of variation were less than 10% both within and between batches, indicating the good reproducibility of the method. The study found that the test result was positive when the serum dilution was 217, indicating the high sensitivity of the method. A total of 24 positive sera and 40 negative sera were tested using the well-established ELISA. The study also established an indirect ELISA assay with good specificity and sensitivity for the detection of antibodies to bovine rotavirus. Overall, the results suggest that the indirect ELISA method developed in this study is an effective test for detecting such antibodies.

A multiplex real-time fluorescence-based quantitative PCR assay for calf diarrhea viruses

Introduction

Calf diarrhea is a significant condition that has a strong effect on the cattle industry, resulting in huge economic losses annually. Bovine torovirus (BToV), bovine enterovirus (BEV), bovine norovirus (BNoV), bovine coronavirus (BCoV), bovine rotavirus (BRV), and bovine viral diarrhea virus (BVDV) are key pathogens that have been implicated in calf diarrhea. Among these viruses, there remains limited research on BToV, BEV, and BNoV, with no available vaccines or drugs for their prevention and control. Although commercial vaccines exist for BCoV, BRV, and BVDV, the prevalence of these diseases remains high.

Methods

To address this issue, we developed a multiplex real-time fluorescence quantitative PCR method for detecting BToV, BEV, BNoV, BCoV, BRV, and BVDV. This method can be used to effectively monitor the prevalence of these six viruses and serve as a reference for future prevention and control strategies. In this study, we specifically designed primers and probes for the BNoV Rdrp, BEV 5'UTR, BToV M, BCoV N, BRV NSP5, and BVDV 5'UTR genes.

Results

This method was determined to be efficient, stable, and sensitive. The lowest detectable levels of plasmids for BNoV, BEV, BToV, BRV, BCoV, and BVDV were 1.91 copies/μL, 96.0 copies/μL, 12.8 copies/μL, 16.4 copies/μL, 18.2 copies/μL, and 65.3 copies/μL, respectively. Moreover, the coefficients of variation for all six detection methods were < 3%; they also exhibited a strong linear relationship (R2 ≥ 0.98), and an amplification efficiency of 90%-110%. A total of 295 fecal and anal swabs were collected from calves with diarrhea in Guangdong, China. The positive rates for BToV, BEV, BNoV, BCoV, BR, and BVDV were determined to be 0.34% (1/295), 6.10% (18/295), 0.68% (2/295), 1.36% (4/295), 10.85% (32/295), and 2.03% (6/295), respectively. Notably, BEV and BRV exhibited the highest prevalence.

Discussion

Additionally, this study identified the occurrence of BToV and BNoV in Guangdong for the first time. In summary, this study successfully established an effective method for detecting several important bovine viruses; ultimately, this holds strong implications for the future development of the cattle industry.

Establishment and application of multiplex droplet digital polymerase chain reaction assay for bovine enterovirus, bovine coronavirus, and bovine rotavirus

Bovine enterovirus (BEV), bovine coronavirus (BCoV), and bovine rotavirus (BRV) are still the major worldwide concerns in the health care of cattle, causing serious economic losses in the livestock industry. It is urgent to establish specific and sensitive methods to detect viruses for the early control of diseases. Droplet digital PCR (ddPCR) has been proposed to effectively detect viral particles, and it does not involve Ct values or standard curves. In this study, we designed specific primers and probes, based on conserved regions of viral genomes, to optimize protocols for a dual ddPCR assay for detecting BCoV and BRV and a multiplex ddPCR assay for BEV, BCoV, and BRV. Sensitivity assays revealed that the lower limit of detection for qPCR was 1,000 copies/μL and for ddPCR for BEV, BCoV, and BRV, 2.7 copies/μL, 1 copy/μL and 2.4 copies/μL, respectively. Studying 82 samples collected from diarrheal calves on a farm, our dual ddPCR method detected BCoV, BRV, and co-infection at rates of 18.29%, 14.63%, and 6.1%, respectively. In contrast, conventional qPCR methods detected BCoV, BRV, and co-infection at rates of 10.98%, 12.2%, and 3.66%, respectively. On the other hand, studying 68 samples from another farm, qPCR detected BCoV, BRV, BEV, and co-infection of BCoV and BEV at rates of 14.49%, 1.45%, 5.80%, and 1.45%, respectively. Our multiplex ddPCR method detected BCoV, BRV, BEV, co-infection of BCoV and BEV, and co-infection of BRV and BEV. at rates of 14.49%, 2.9%, 8.7%, 2.9%, and 1.45%, respectively. Studying 93 samples from another farm, qPCR detected BCoV, BRV, BEV, and co-infection of BCoV and BEV was detected at rates of 5.38%, 1.08%, 18.28%, and 1.08%, respectively. Co-infection of BCoV, BRV, BEV, BCoV, and BEV, and co-infection of BRV and BEV, were detected by multiplex ddPCR methods at rates of 5.38%, 2.15%, 20.45%, 1.08%, and 1.08%, respectively. These results indicated that our optimized dual and multiplex ddPCR methods were more effective than conventional qPCR assays to detect these viral infections.

Alterations of microbiota and metabolites in the feces of calves with diarrhea associated with rotavirus and coronavirus infections

The changes in the composition of intestinal microbiota and metabolites have been linked to digestive disorders in calves, especially neonatal calf diarrhea. Bovine rotavirus (BRV) and bovine coronavirus (BCoV) are known to be the primary culprits behind neonatal calf diarrhea. In this study, we analyzed changes in the fecal microbiota and metabolites of calves with neonatal diarrhea associated with BRV and BCoV infection using high-throughput 16S rRNA sequencing and metabolomics technology. The microbial diversity in the feces of calves infected with BRV and BCoV with diarrhea decreased significantly, and the composition changed significantly. The significant increase of Fusobacterium and the reductions of some bacteria genera, including Faecalibacterium, Bifidobacterium, Ruminococcus, Subdoligranulum, Parabacteroides, Collinsella, and Olsenella, etc., were closely related to diarrhea associated with BRV and BCoV infection. Metabolites in the feces of BRV and BCoV-infected calves with diarrhea were significantly changed. Phosphatidylcholine [PC; 16:1(9 Z)/16:1(9 Z)], lysophosphatidylethanolamine (LysoPE; 0:0/22:0), lysophosphatidylcholine (LysoPC; P-16:0) and LysoPE (0:0/18:0) were significantly higher in the feces of BRV-infected calves with diarrhea. In contrast, some others, such as desthiobiotin, were significantly lower. BRV infection affects glycerophospholipid metabolism and biotin metabolism in calves. Two differential metabolites were significantly increased, and 67 differential metabolites were significantly reduced in the feces of BCoV-infected calves with diarrhea. Seven significantly reduced metabolites, including deoxythymidylic acid (DTMP), dihydrobiopterin, dihydroneopterin triphosphate, cortexolone, cortisol, pantetheine, and pregnenolone sulfate, were enriched in the folate biosynthesis, pantothenate and CoA biosynthesis, pyrimidine metabolism, and steroid hormone biosynthesis pathway. The decrease in these metabolites was closely associated with increased harmful bacteria and reduced commensal bacteria. The content of short-chain fatty acids (SCFAs) such as acetic acid and propionic acid in the feces of BRV and BCoV-infected calves with diarrhea was lower than that of healthy calves, which was associated with the depletion of SCFAs-producing bacteria such as Parabacteroides, Fournierella, and Collinsella. The present study showed that BRV and BCoV infections changed the composition of the calf fecal microbiota and were associated with changes in fecal metabolites. This study lays the foundation for further revealing the roles of intestinal microbiota in neonatal calf diarrhea associated with BRV and BCoV infection.

Analysis of Fecal Microbial Changes in Young Calves Following Bovine Rotavirus Infection

The objective of the present study was to identify changes in fecal microbiota and predict the functional features of healthy calves and those infected with rotavirus over time. Six Holstein calves (average body weight 43.63 ± 1.19 kg, age-matched within 5-7 d) were randomly selected and distributed into two groups which contained three calves each. Fecal samples were taken 3 days before inoculation and on days 1 and 7 post-inoculation. The 16S rRNA gene amplicon sequencing was performed. Bacterial diversity tended to decrease in the rota group, as indicated by the alpha (evenness, p = 0.074 and Shannon, p = 0.055) and beta (Bray-Curtis dissimilarity, p = 0.099) diversity at 1 day post-inoculation. Differences in the bacterial taxa between healthy and rota-infected calves were detected using a linear discriminant analysis effect size (LDA > 2.0, p < 0.05). Rota calves had a higher abundance of certain bacterial taxa, such as Enterococcus, Streptococcus, and Escherichia-Shigella, and a lower abundance of bacteria that contribute to the production of short-chain fatty acids, such as Alistipes, Faecalibacterium, Pseudoflavonifractor, Subdoligranulum, Alloprevotella, Butyricicoccus, and Ruminococcus, compared to the healthy calves. The observed changes in the fecal microbiota of the rota-infected group compared to the healthy group indicated potential dysbiosis. This was further supported by significant differences in the predicted functional metagenomic profiles of these microbial communities. We suggest that calves infected with bovine rotavirus had bacterial dysbiosis, which was characterized by lower diversity and fewer observed genera than the fecal microbiota of healthy calves.

Affinity Peptide-based Electrochemical Biosensor for the Highly Sensitive Detection of Bovine Rotavirus

Bovine diarrhea is a major concern in the global bovine industry because it can cause significant financial damage. Of the many potential infectious agents that can lead to bovine diarrhea, bovine rotavirus (BRV) is a particular problem due to its high transmissibility and infectivity. Therefore, it is important to prevent the proliferation of BRV using an early detection system. This study developed an affinity peptide-based electrochemical method for use as a rapid detection system for BRV. A BRV-specific peptide was identified via the phage display technique and chemically synthesized. The synthetic peptide was immobilized on a gold electrode through thiol-gold interactions. The performance of the BRV specific binding peptides was evaluated using square wave voltammetry. The developed detection system exhibited a low detection limit (5 copies/mL) and limit of quantitation (2.14 × 10² copies/mL), indicating that it is a promising sensor platform for the monitoring of BRV.

Isolation and Characterization of Bovine RVA from Northeast China, 2017-2020

Group A rotaviruses (RVAs) are major enteric pathogens causing infections in calves. To investigate the epidemiological characteristics and genetic diversity of bovine rotavirus (BRV), 233 fecal samples were collected from calves with diarrhea in northeast China. The samples were analyzed for sequences encoding the inner capsid protein VP6 (subgroup) and the outer capsid proteins VP7 and VP4 (G and P type, respectively) using RT-PCR. Ten of the 233 samples (4.3%) were identified as BRV positive and were used for virus isolation and sequence analysis, revealing that all strains analyzed were of the G6P[1] genotype. The isolates exhibited high VP6 sequence identity to the USA cow RVA NCDV strain (>99% amino acid identity) and were further shown to be closely related to Japanese cow RVA BRV101 and Israelian human RVA G6P[1] strains, with >99% amino acid identity to VP7 and VP4 proteins, respectively. Comparative analyses of genome-predicted amino acid sequences between the isolates and the NCDV strains indicated that the antigenicity and infectivity of the strains isolated had changed. In this study, BRV genotypes and the genetic diversity among vaccinated cattle herds were monitored to provide epidemiological data and references for early diagnosis, allowing for early detection of new, potentially pathogenic RVA strains.

Genetic Characterisation of South African and Mozambican Bovine Rotaviruses Reveals a Typical Bovine-like Artiodactyl Constellation Derived through Multiple Reassortment Events

This study presents whole genomes of seven bovine rotavirus strains from South Africa and Mozambique. Double-stranded RNA, extracted from stool samples without prior adaptation to cell culture, was used to synthesise cDNA using a self-annealing anchor primer ligated to dsRNA and random hexamers. The cDNA was subsequently sequenced using an Illumina MiSeq platform without prior genome amplification. All strains exhibited bovine-like artiodactyl genome constellations (G10/G6-P[11]/P[5]-I2-R2-C2-M2-A3/A11/A13-N2-T6-E2-H3). Phylogenetic analysis revealed relatively homogenous strains, which were mostly related to other South African animal strains or to each other. It appears that these study strains represent a specific bovine rotavirus population endemic to Southern Africa that was derived through multiple reassortment events. While one Mozambican strain, MPT307, was similar to the South African strains, the second strain, MPT93, was divergent from the other study strains, exhibiting evidence of interspecies transmission of the VP1 and NSP2 genes. The data presented in this study not only contribute to the knowledge of circulating African bovine rotavirus strains, but also emphasise the need for expanded surveillance of animal rotaviruses in African countries in order to improve our understanding of rotavirus strain diversity.

Cryptosporidium spp. Infections in Combination with Other Enteric Pathogens in the Global Calf Population

Simple Summary

The factors “diagnostic”, “health status of the sampled animals”, and “geographical region” explained the majority of the variance of Cryptosporidium spp. (Crypto) prevalence in the global calf population across the literature. The chance of detecting bovine rotavirus (BRV), bovine coronavirus (BCoV), and enterotoxigenic Escherichia coli F5 (K99) (ETEC) in calves with diarrhoea was lower in the presence of Crypto compared to calves without Crypto. This may indicate an inhibition effect between BRV, BCoV, ETEC, and Crypto.

Abstract

The most common worldwide diarrhoea-causing agents in neonatal calves are Cryptosporidium spp. (Crypto), bovine rotavirus (BRV), bovine coronavirus (BCoV), and enterotoxigenic Escherichia coli F5 (K99) (ETEC). Crypto is a zoonotic pathogen of diarrhoea in humans, particularly for children and immunocompromised adults. Four weighted-stratified random-effect meta-analyses including meta-regression analyses were performed to calculate the worldwide mean prevalence of Crypto and associated concurrent infections with BRV, BCoV and ETEC, as well as their potential influencing factors. The meta-analysis incorporated 28 studies (56 substudies) in 17 countries that determined the presence or absence of concurrent infections with Crypto in the global calf population. Approximately half of all considered studies presented here were conducted in Europe independently of the type of infections with Crypto. Within Europe, the highest estimated mean Crypto-BRV prevalence was identified in Ireland (16.7%), the highest estimated mean Crypto-BCoV prevalence was detected in the United Kingdom (4.3%), and the highest estimated mean Crypto-ETEC prevalence across the literature was determined in Turkey (4.7%). The chance of detecting BRV, BCoV, and ETEC in calves with diarrhoea was 0.8 (confidence interval (CI): 0.6–1.0), 0.7 (CI: 0.5–1.0) and 0.6 (CI: 0.4–0.9) lower in the presence of Crypto compared to calves without Crypto. This may indicate an inhibitory effect between BRV, BCoV, ETEC, and Crypto in calves. The variance in the published prevalence across the literature can mainly be explained by the “diagnostic” factor (R² min–max: 0.0–40.3%), followed by the “health status of the sampled animals” (R² min–max: 1.4–27.3%) and “geographical region” (R² min–max: 5.9–23.6%).

Prevalence of Worldwide Neonatal Calf Diarrhoea Caused by Bovine Rotavirus in Combination with Bovine Coronavirus, Escherichia coli K99 and Cryptosporidium spp.: A Meta-Analysis

Multiple enteropathogens such as bovine rotavirus (BRV), bovine coronavirus (BCoV), Escherichia coli K99 (ETEC) and Cryptosporidium spp. (Crypto) are the most common causes of calf diarrhoea during the first 30 days of animal age. Three weighted-stratified random-effects meta-analyses were performed to calculate the worldwide prevalence of mixed infections of the causative agents (i.e., BRV-BCoV, BRV-ETEC, BRV-Crypto) and their potential influencing factors. The meta-analysis covered 41 studies (94 sub-studies) in 21 countries that determined the presence or absence of mixed infections in global calf populations. The highest worldwide estimated pooled prevalence was identified for BRV-Crypto (6.69%), followed by BRV-BCoV (2.84%), and BRV-ETEC (1.64%). The chance of detecting BCoV in calves with diarrhoea was 1.83 higher in the presence of BRV compared to calves without BRV, whereby an inhibition effect (odds ratio: 0.77) was determined between BRV and Crypto infections. The diagnostic methods were identified as a significant influencing factor in the detection of all considered mixed infections, while the other analysed factors differed in relation to their effect on prevalence. In contrast to BRV-BCoV, the prevalence of BRV-ETEC and BRV-Crypto mixed infections followed the course of individual ETEC and Crypto prevalence related to the age class of the sampled animals.

Simultaneous Detection of Bovine Rotavirus, Bovine Parvovirus, and Bovine Viral Diarrhea Virus Using a Gold Nanoparticle-Assisted PCR Assay With a Dual-Priming Oligonucleotide System

Bovine rotavirus (BRV), bovine parvovirus (BPV), and bovine viral diarrhea virus (BVDV) are the pathogens that cause diarrhea primarily in newborn calves. A mixed infection of BRV, BPV, and BVDV makes clinical diagnosis difficult. In this study, we designed dual-priming oligonucleotide (DPO) primers the VP6 gene of BRV, VP2 gene of BPV, and 5′UTR gene of BVDV and synthesized gold nanoparticles (GNPs) with an average diameter of 10 nm. We combined the DPOs with the GNPs to develop a DPO-nanoPCR assay for detecting BRV, BPV, and BVDV. The annealing temperature, primer concentration, and GNP concentration were optimized for this assay. Compared to a conventional PCR assay, the DPO-nanoPCR assay allowed the use of a wider range of annealing temperatures (41–65°C) to effectively amplify target genes. PCR amplification was the most efficient at 56.2°C using conventional primers. The optimal volume of all the primers (10 μM) was 1.0 μL. The optimal volume of GNPs (10 nM) for all the reactions was 0.5 μL. The detection limits of DPO-nanoPCR for pMD19-T-VP6, pMD19-T-VP2, and pMD19-T-5′UTR were 9.40 × 10² copies/μL, 5.14 × 10³ copies/μL, and 4.09 × 10¹ copies/μL, respectively; and those using conventional PCR were 9.40 × 10⁴ copies/μL, 5.14 × 10⁵ copies/μL, and 4.09 × 10⁴ copies/μL, respectively. The sensitivity of DPO-nanoPCR was at least 100-fold higher than that of conventional PCR. The specificity detection showed that the DPO-nanoPCR was able to specifically detect BRV, BPV, and BVDV. Use of clinical samples indicated that target viruses can be detected accurately. Thus, DPO-nanoPCR is a new powerful, simple, specific, and sensitive tool for detecting mixed infections of BRV, BPV, and BVDV.

Development of a Colloidal Gold Immunochromatographic Strip Assay for Rapid Detection of Bovine Rotavirus

Bovine rotavirus (BRV) is one of main pathogens responsible for diarrhea, fever, and vomiting. In this study, we developed a colloidal gold immunochromatographic test strip for detecting BRV according to the principle of double-antibody sandwich. The monoclonal antibodies (mAbs) and polyclonal antibodies (pAbs) were prepared and purified. On the strip, the purified mAbs labeled with the colloidal gold were used as the detector, and the goat anti-mouse antibodies and purified pAbs were coated on the nitrocellulose membranes as the control line and the test line, respectively. We optimized different reaction conditions, including the amount of mAbs, the pH of colloidal gold solution, coating solution, blocking solution, sample pad treatment solution, antibody concentration in control line, and antibody concentration in detection line. In specificity assay, the strip had high specificity in detecting BRV. No cross-reaction was observed in detecting other viruses. The detection sensitivity of the strip was found to be 1 × 10³ TCID₅₀/0.1 mL. Two hundred twenty clinical samples were detected with the strip compared to reverse transcription-polymerase chain reaction. No false-negative or false-positive results were found, and the results obtained by the two methods were similar. In conclusion, we developed a novel immunochromatographic strip to rapidly detect BRV. The strip developed exhibited high sensitivity and specificity for BRV detection. It could be a rapid, convenient, and effective method for the rapid diagnosis of BRV infection in the fields.

Immunobiotics for the Bovine Host: Their Interaction with Intestinal Epithelial Cells and Their Effect on Antiviral Immunity

The scientific community has reported several cases of microbes that exhibit elevated rates of antibiotic resistance in different regions of the planet. Due to this emergence of antimicrobial resistant microorganisms, the use of antibiotics as promoters of livestock animals' growth is being banned in most countries around the world. One of the challenges of agricultural immunology therefore is to find alternatives by modulating the immune system of animals in drug-independent safe food production systems. In this regard, in an effort to supplant antibiotics from bovine feeds, several alternatives were proposed including the use of immunomodulatory probiotics (immunobiotics). The purpose of this review is to provide an update of the status of the modulation of intestinal antiviral innate immunity of the bovine host by immunobiotics, and the beneficial impact of immunobiotics on viral infections, focused on intestinal epithelial cells (IECs). The results of our group, which demonstrate the capacity of immunobiotic strains to beneficially modulate Toll-like receptor 3-triggered immune responses in bovine IECs and improve the resistance to viral infections, are highlighted. This review provides comprehensive information on the innate immune response of bovine IECs against virus, which can be further investigated for the development of strategies aimed to improve defenses in the bovine host.

Serum interleukin-6 as a prognostic marker in neonatal calf diarrhea

Neonatal calf diarrhea is still one of the most important diseases in calf rearing, and severe diarrhea has a marked effect on animal welfare. Furthermore, significant economic losses can result from this disease due to high mortality rates, high medical costs, and low weight gain. To avoid a fatal outcome of the disease, it is crucial that vulnerable calves are identified as early as possible. Interleukin-6 is described as an early and reliable prognostic marker in several diseases. In this study, 20 scouring calves were tested by ELISA for their IL-6 serum concentrations. Samples were collected twice, at the beginning of diarrhea and 7 to 10 d later. Regarding the clinical outcome after 7 to 10 d, calves were classified as recovered or nonrecovered. A receiver operating characteristic analysis was conducted to determine the prognostic value of IL-6 for the progress of clinical symptoms. At the beginning of diarrhea, the IL-6 concentration was significantly higher in nonrecovering calves compared with those that recover 7 to 10 d after the onset of diarrhea. Interleukin-6 proved to be a useful additional parameter in the clinical examination. High initial IL-6 values can support the decision for closer monitoring and an adapted therapeutic strategy for the respective calves. This may help to prevent unnecessary animal suffering and reduce economic losses.

Lumazine Synthase Fused to Bovine Rotavirus VP8d as a Scaffold for Antigen Production in Tobacco Chloroplasts

Lumazine synthase from Brucella spp. (BLS) is a highly immunogenic decameric protein which can accommodate foreign polypeptides or protein domains fused to its N-termini, markedly increasing their immunogenicity. The inner core domain (VP8d) of VP8 spike protein from bovine rotavirus is responsible for viral adhesion to sialic acid residues and infection. It also displays neutralizing epitopes, making it a good candidate for vaccination. In this work, the BLS scaffold was assessed for the first time in plants for recombinant vaccine development by N-terminally fusing BLS to VP8d and expressing the resulting fusion (BLSVP8d) in tobacco chloroplasts. Transplastomic plants were obtained and characterized by Southern, northern and western blot. BLSVP8d was highly expressed, representing 40% of total soluble protein (4.85 mg/g fresh tissue). BLSVP8d remained soluble and stable during all stages of plant development and even in lyophilized leaves stored at room temperature. Soluble protein extracts from fresh and lyophilized leaves were able to induce specific neutralizing IgY antibodies in a laying hen model. This work presents BLS as an interesting platform for highly immunogenic injectable, or even oral, subunit vaccines. Lyophilization of transplastomic leaves expressing stable antigenic fusions to BLS would further reduce costs and simplify downstream processing, purification and storage, allowing for more practical vaccines.

Detection and genotyping of group A rotaviruses isolated from sewage samples in Monastir, Tunisia between April 2007 and April 2010

AIMS

To ascertain the viral load, the distribution of G and P types of group A rotaviruses (RV-A) in sewage samples and to compare strains in clinical, animal and environmental samples.

METHODS AND RESULTS

During our study from April 2007 to April 2010, 518 samples of raw and treated sewage were collected from two biological sewage treatment plants (STPs) located in the Monastir region, Tunisia. RV-A was detected by real-time RT-PCR in 375 (72·4%) sewage samples. According to the quantification results of RV-A, it appears that the viral load in raw and treated sewage of the two STPs was quite similar (P = 0·735). The genotyping of RV-A strains detected in sewage samples showed a great diversity with 10 G types and 8 P types. Most of them were described as common in humans, but we also detected genotypes commonly found in animals. All the genotypes detected in two previous studies performed in our laboratory on clinical and bovine samples were also found in environmental samples. However, some genotypes commonly found in animal were only found in sewage samples.

CONCLUSION

The comparison of environmental, clinical and animal data suggests that STPs may convey not only human sewage but also animal wastes, both of them contaminated with numerous RV-A strains which are not efficiently eliminated by the sewage treatment process and may spread to surface waters.

SIGNIFICANCE AND IMPACT OF THE STUDY

This work demonstrates the potential release of human and animal RV-A into water sources, representing a public health risk, by inducing gastroenteritis in population, but also by increasing the risk of zoonotic transmission and formation of reassortant viruses which could get a higher infectious potential. Our findings also suggest that monitoring of sewage may provide an additional tool to determine the epidemiology of RV-A circulating in a given community.

Rotavirus diarrhea in bovines and other domestic animals

Rotavirus diarrhea is the major cause of death of millions of children in developing countries besides causing economically significant malady in neonates of many domestic animals. In neonates, the infection is non-viremic, have very short incubation period, and manifests profuse diarrhea and severe dehydration. Concurrent infection with secondary pathogens may augment the disease severity. Diarrhea occurs due to virus-mediated destruction of absorption efficient enterocytes, activation of enteric nervous system, or due to a rotavirus enterotoxin. Diagnosis of the infection relies on conventional techniques like isolation in MA 104 cell lines, electron microscopy, electro-pherotyping, and various serological tests. Presently, diagnosis and molecular typing is performed using serotype specific RT-PCR, sequencing or genomic hybridization techniques. As the rotaviruses are known to exhibit extreme genetic diversity and outplay disinfection procedures, eradication of the pathogen is often difficult. Hence, for prevention, good management practices coupled with vaccination of dam for protecting young ones, has to be practiced. Recently, new generation prophylactic strategies including DNA vaccines, subunit vaccines, virus-like particles (VLPs) and edible vaccines have been found to induce sufficient levels of passive immunity. Aside to the infection in animals, zoonotic significance of the animal rotaviruses has to be further unearthed. In this review, efforts have been made to highlight the importance and prevalence of the disease in bovines, its pathogenesis along with preventive measures, salient features of rotaviruses and their inter-species transmission abilities, zoonotic implications, and a concise account of the infection in various domestic animals and poultry.

Crystallization and preliminary X-ray diffraction analysis of the carbohydrate-recognizing domain (VP8*) of bovine rotavirus strain NCDV

The infectivity of rotavirus is dramatically enhanced by proteolytic cleavage of its outer layer VP4 spike protein into two functional domains, VP8* and VP5*. The carbohydrate-recognizing domain VP8* is proposed to bind sialic acid-containing host cell-surface glycans and this is followed by a series of subsequent virus-cell interactions. Live attenuated human and bovine rotavirus vaccine candidates for the prevention of gastroenteritis have been derived from bovine rotavirus strain NCDV. The NCDV VP8*(64-224) was overexpressed, purified to homogeneity and crystallized in the presence of an N-acetylneuraminic acid derivative. X-ray diffraction data were collected to a resolution of 2.0 A and the crystallographic structure of NCDV VP8*(64-224) was determined by molecular replacement.

Passive immunity to bovine rotavirus in newborn calves fed colostrum supplements from cows immunized with recombinant SA11 rotavirus core-like particle (CLP) or virus-like particle (VLP) vaccines

Heterotypic passive immunity to IND (P/5/G6) bovine rotavirus (BRV) was evaluated. Three groups of calves (n = 5 per group) were fed 1% pooled colostrum supplements (birth to 7 days of age) from BRV seropositive cows vaccinated with recombinant SA11(P/2/G3) rotavirus-like particles (VLPs), recombinant SA11 rotavirus core-like particles (CLPs), or inactivated SA11 rotavirus (SA11). Control calves (n = 5 per group) received either pooled colostrum from unvaccinated (BRV field exposure seropositive) control cows, or no colostrum. IgG1 antibody titers to IND BRV for the pooled colostrum were: 1,048,576 (VLP); 1,048,576 (CLP); 262,144 (SA11); and 16,384 (control colostrum). Elevated titers of BRV neutralizing (VN) antibodies were present in VLP colostrum (98,000), and SA11 colostrum (25,000), but not in CLP colostrum (1400), compared to colostrum from nonvaccinates (2081). Calves were orally inoculated with virulent IND BRV at 2 days of age and challenged at post-inoculation day (PID) 21. Calves were monitored daily for diarrhea and faecal BRV shedding through PID 10 and post-challenge day (PCD) 10. After colostrum feeding, the IgG1 antibody titers were highest in serum and faeces of calves fed VLP and CLP colostrum, but VN and IgA antibodies were highest in calves fed VLP colostrum. After BRV inoculation, calves fed colostrum from vaccinated cows had significantly fewer days of BRV-associated diarrhea and BRV shedding than control calves. All calves fed VLP colostrum were protected from diarrhea after BRV inoculation; two calves shed BRV. In the CLP colostrum group, one calf developed BRV-associated diarrhea and all calves shed virus. In the SA11 colostrum group, three calves developed BRV-associated diarrhea and four calves shed virus. BRV-associated diarrhea and shedding occurred in 9 of 10 control calves. Active IgM antibody responses occurred in faeces and/or serum of most calves after BRV inoculation. However, the highest active antibody responses (IgM and IgG1 in serum, and IgM, IgG1 or IgA in faeces) after BRV inoculation were in calves fed control or no colostrum, in association with clinical diarrhea in most of these calves. After challenge at PID 21, BRV-associated diarrhea and shedding were of short duration or absent, in all groups. These results demonstrate the efficacy of colostrum from VLP vaccinated cows to provide heterologous, passive protection against BRV diarrhea and shedding in calves. In comparison, calves fed CLP or SA11 colostrum were only partially protected against BRV diarrhea or shedding.

Studies on the survival of aerosolized bovine rotavirus (UK) and a murine rotavirus

The effect of relative humidity (RH) and temperature on the survival of airborne bovine rotavirus UK isolate (BRV-UK) and a murine rotavirus (MRV) was studied. In any one experiment, the virus under test was suspended in tryptose phosphate broth (TPB) supplemented with uranine (physical tracer) and an antifoam, was aerosolized using a Collison nebulizer into the rotating drum with the RH at either low (30 +/- 5%), medium (50 + 5%) or high (80 +/- 5%) level at 20 +/- 1 degrees C. Following a 15-min period of viral aerosol stabilization, sequential samples of drum air were collected using an All-Glass Impinger (AGI) for 24 h post-aerosolization. Both of the rotavirus isolates were found to survive best at medium RH level and high RH was found least favorable for the survival of these aerosolized rotaviruses. The survival pattern of aerosolized MRV was found to be the best when compared with survival pattern of all animal and human rotavirus isolates studies performed under aerosolized conditions in our laboratory. The findings of these experiments confirm and extend our previous reports on the survival of other animal and human aerosolized rotaviruses and emphasize the fact that air may be one of the vehicles for their dissemination and could explain why it is difficult to control nosocomial outbreaks of rotavirus gastroenteritis and to keep animal colonies rotavirus-free.

Standardization and kinetics of in vitro bovine blood lymphocyte stimulation with bovine rotavirus

Two groups of 3-month old calves were immunized intramuscularly with attenuated bovine rotavirus and boosted 21 and 42 days later. The first group of three calves were vaccinated with live virus emulsified with incomplete Freund's adjuvant (IFA) and the second group was immunized with live virus suspended in phosphate buffered saline (PBS). Three other calves, serving as controls, were inoculated with PBS emulsified with IFA. The specific cell-mediated and antibody responses of the animals were studied. Preliminary analysis of in vitro peripheral blood lymphocyte transformation to bovine rotavirus determined optimal conditions as: 96 h culture period, 5 X 10(5) cells per culture in RPMI 1640 medium containing 10% heat-inactivated bovine fetal serum and the use of inactivated virus in the cell culture at a concentration of 5 X 10(6) median tissue culture infective dose before inactivation. Specific blastic stimulation was observed on calves immunized with the rotavirus emulsified with IFA after the second and third vaccine inoculation with stimulation index values varying from 2.00 to 5.73. Serum neutralizing antibody titers of 1/25,600 were also induced in the same calves. Calves immunized with rotavirus-PBS suspension developed a mean antibody titer of 1/1,600, but showed no specific lymphocyte stimulation. No increase in specific immune responses was detected in the control animals.

Plaque assay of bovine rotavirus

Incorporation of trypsin and diethylaminoethyl-dextran in the overlay was found to be necessary for infectivity assay of the UK strain of bovine rotavirus by plaque assays. Small plaques of about 1 mm in radius were formed in BGM cells. Large plaques of about 3–4 mm in radius were consistently produced in monolayers of secondary calf kidney cultures.