Immunogens of rotaviruses

Surface Display of Antigen Protein VP8* of Porcine Rotavirus on Bacillus Subtilis Spores Using CotB as a Fusion Partner

Porcine rotavirus is a major cause of acute viral gastroenteritis in suckling piglets, and vaccination is considered to be an effective measure to control these infections. The development of a live mucosal vaccine using Bacillus subtilis spores as an antigen delivery vehicle is a convenient and attractive vaccination strategy against porcine rotavirus. In this study, a shuttle vector was constructed for the spore surface display of the spike protein VP8* from porcine rotavirus (the genotype was G5P[7]). A successful display of the CotB-VP8* fusion protein on the spore surface was confirmed by Western blot and immunofluorescence microscopy analysis. The capacity for immune response generated after immunization with the recombinant strain was evaluated in a mouse model. The intestinal fecal IgA and serum IgG were detected by enzyme-linked-immunosorbent serologic assay (ELISA). Importantly, recombinant strain spores could elicit strong specific mucosal and humoral immune responses. These encouraging results suggest that recombinant B. subtilis BV could provide a strategy for a potential novel application approach to the development of a new and safe mucosal subunit vaccine against porcine rotavirus.

Rotavirus C: prevalence in suckling piglets and development of virus-like particles to assess the influence of maternal immunity on the disease development

Rotavirus C (RVC) has been detected increasingly in humans and swine in different countries, including the US. It is associated with significant economic losses due to diarrheal disease in nursing piglets. In this study we aimed: (1) to determine the prevalence of RVC in healthy and diarrheic suckling piglets on US farms; and (2) to evaluate if maternal antibody (Ab) levels were associated with protection of newborn suckling piglets against RVC. There was a significantly higher prevalence (p = 0.0002) of litters with diarrhea born to gilts compared with those born to multiparous sows. Of 113 nursing piglet fecal samples tested, 76.1% were RVC RNA positive. Fecal RVC RNA was detected in significantly (p = 0.0419) higher quantities and more frequently in piglets with diarrhea compared with healthy ones (82.5 vs. 69.9%). With the exception of the historic strain Cowden (G1 genotype), field RVC strains do not replicate in cell culture, which is a major impediment for studying RVC pathogenesis and immunity. To circumvent this, we generated RVC virus-like particles (VLPs) for Cowden (G1), RV0104 (G3) and RV0143 (G6) and used them as antigens in ELISA to detect swine RVC Abs in serum and milk from the sows. Using RVC-VLP Ab ELISA we demonstrated that sows with diarrheic litters had significantly lower RVC IgA and IgG Ab titers in milk compared to those with healthy litters. Thus, our data suggest that insufficient lactogenic protection provided by gilts plays a key role in the development of and the increased prevalence of clinical RVC disease.

Preparation of 4-arm star PELA and its encapsulation of rotavirus for drug delivery

A relatively high molecular weight of 4-arm star PELA was obtained by ring-opening polymerization of l-lactic acid O-carboxyanhydride with 4-arm-PEG in the presence of DMAP as an initiator. The results via(1)H NMR and (13)C NMR show that the end of the star PELA chain is a hydroxyl group and the central core is a PEG group. Rotavirus (strain SA11) was incorporated into 4-arm star PELA microspheres formulated by the water in oil in water emulsification solvent extraction method. The microspheres produced were spherical, and the mean diameter was 1.34 μm with a narrow size distribution. The drug release profile displayed a low burst release effect of 1.8% on the first day and a sustained release of antigen over 100 days. After the immunization of mice, the microsphere-entrapped RV elicited improved and long-lasting IgA and IgG antibody response in serum detected by ELISA in comparison to the free RV antigen. This study shows that 4-arm-PEG is an effective initiator for the ring-opening polymerization of Lac-OCA by DMAP as an initiator and that the resulting polymer is useful as a delivery system for the rotavirus vaccine.

Oral vaccination with the porcine rotavirus VP4 outer capsid protein expressed by Lactococcus lactis induces specific antibody production

The objective of this study to design a delivery system resistant to the gastrointestinal environment for oral vaccine against porcine rotavirus. Lactococcus lactis NZ9000 was transformed with segments of vP4 of the porcine rotavirus inserted into the pNZ8112 surface-expression vector, and a recombinant L. lactis expressing VP4 protein was constructed. An approximately 27 kDa VP4 protein was confirmed by SDS-PAGE , Western blot and immunostaining analysis. BALB/c mice were immunized orally with VP4-expression recombinant L. lactis and cellular, mucosal and systemic humoral immune responses were examined. Specific anti-VP4 secretory IgA and IgG were found in feces, ophthalmic and vaginal washes and in serum. The induced antibodies demonstrated neutralizing effects on porcine rotavirus infection on MA104 cells. Our findings suggest that oral immunization with VP4-expressing L. lactis induced both specific local and systemic humoral and cellular immune responses in mice.

Recombinant porcine rotavirus VP4 and VP4-LTB expressed in Lactobacillus casei induced mucosal and systemic antibody responses in mice

Background

Porcine rotavirus infection is a significant cause of morbidity and mortality in the swine industry necessitating the development of effective vaccines for the prevention of infection. Immune responses associated with protection are primarily mucosal in nature and induction of mucosal immunity is important for preventing porcine rotavirus infection.

Results

Lactobacillus casei expressing the major protective antigen VP4 of porcine rotavirus (pPG612.1-VP4) or VP4-LTB (heat-labile toxin B subunit from Echerichia coli) (pPG612.1-VP4-LTB) fusion protein was used to immunize mice orally. The expression of recombinant pPG612.1-VP4 and pPG612.1-VP4-LTB was confirmed by SDS-PAGE and Western blot analysis and surface-displayed expression on L. casei was verified by immunofluorescence. Mice orally immunized with recombinant protein-expressing L. casei produced high levels of serum immunoglobulin G (IgG) and mucosal IgA. The IgA titters from mice immunized with pPG612.1-VP4-LTB were higher than titters from pPG612.1-VP4-immunized mice. The induced antibodies demonstrated neutralizing effects on RV infection.

Conclusion

These results demonstrated that VP4 administered in the context of an L. casei expression system is an effective method for stimulating mucosal immunity and that LTB served to further stimulate mucosal immunity suggesting that this strategy can be adapted for use in pigs.

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.

Frequency of group A rotavirus in diarrhoeic calves in Brazilian cattle herds, 1998-2002

The frequency of group A bovine rotavirus (gpA BRV) in calves from 1998 to 2002 was determined by the polyacrylamide gel electrophoresis technique in 2177 faecal samples, of which 1898 samples were diarrhoeic and 279 were of normal consistency (control group) that were collected from asymptomatic calves for comparative purposes. The animals were from beef and dairy cattle herds (n = 321) from 158 counties in seven States (Paraná, São Paulo, Minas Gerais, Mato Grosso do Sul, Mato Grosso, Goiás and Rondônia) and four Brazilian geographical regions (south, south-east, centre-west, and north). GpA BRV was detected in 19.4% (369/1898; p = 0.0001) of the samples collected in calves with diarrhoea and in only 2.2% (6/279; p = 0.0001) of the faeces with normal consistency. The proportion of positive samples collected from beef and dairy cattle herds was 22.8% (205/899; p = 0.0001) and 16.4% (169/999; p = 0.0005), respectively. In relation to age, a higher prevalence of infections was found in calves up to 30 days old, where 33.0% (189/573; p = 0.0001) and 20.2% (138/683; p = 0.0001) of the diarrhoeic faecal samples from beef and dairy cattle herds, respectively, were positive for gpA BRV. These results show the possible importance of inclusion of gpA BRV in the management of neonatal calf diarrhoea in Brazilian cattle herds.

The synthesis and biological evaluation of lactose-based sialylmimetics as inhibitors of rotaviral infection

Rotaviruses are the most significant cause of gastroenteritis in young children and are responsible for over 600,000 infant deaths annually. The rotaviral haemagglutinin protein (VP8*) of some strains has been implicated in early recognition and binding events of host cell-surface sialoglycoconjugates, and is therefore an attractive target for potential therapeutic intervention. Since N-acetylneuraminic acid alpha(2,3)-linked to galactose is believed to be the minimum binding epitope of rotavirus to host cells, we report here our development of an efficient and flexible synthetic route to a range of lactose-based sialylmimetics of alpha(2,3)-linked thiosialosides. These compounds were biologically evaluated as inhibitors of rotaviral infection using an in vitro neutralisation assay. The results suggest that these lactose-based sialylmimetics are not inhibitors of the rhesus rotavirus strain; however, they do exhibit modest inhibition of the human (Wa) strain, presumably through inhibition of the rotaviral adhesion process.

G and P genotypes of group A rotavirus strains circulating in calves in Brazil, 1996–1999

Fifty fecal samples from calves with diarrhea, positive for group A rotavirus by enzyme immunoassay (EIA) and polyacrylamide gel electrophoresis (PAGE) were analyzed by a nested multiplex reverse transcription/polymerase chain reaction (Nested multiplex/RT-PCR) for identification of P and G genotypes. Samples were collected between 1996 and 1999 from eight dairy and/or beef cattle herds located in the Mato Grosso do Sul, São Paulo, Goiás and Paraná States, Brazil. Complete genotyping was possible in 44 (88%) of the calf fecal samples. The VP7 gene could not be identified in six (12%) of the samples. Whilst the VP4 (P) gene was identified in 100% of samples. The genotypes of 35 (70%) samples corresponded to the NCDV-like (12%), UK-like (40%), B223-like (16%) and KN-4 (2%) reference rotavirus strains, which are commonly found in cattle. Mixed infections were detected in seven (14%) samples, and genotypes observed in two (4%) samples presented unusual combinations, carrying VP4 and VP7 gene of the bovine group A rotavirus (P[11],G8), in other one carrying a VP4 gene of bovine origin (P[1]) and a VP7 gene of swine origin (G5).

Fusion of C3d molecule with bovine rotavirus VP7 or bovine herpesvirus type 1 glycoprotein D inhibits immune responses following DNA immunization

The binding of the complement C3d molecule with receptors on B cells and/or follicular dendritic cells (FDCs) influences the induction of humoral immune responses. For example, C3d fused to an antigen has been shown to have a strong adjuvant effect on antibody production. We investigated the possibility that co-expression of antigen and C3d as a fusion protein could enhance antigen-specific immune responses, following plasmid immunization. One or two copies of murine C3d-cDNA, C3d or (C3d)(2), respectively, were cloned together with bovine rotavirus (BRV) VP7 or bovine herpesvirus type 1 (BHV-1) glycoprotein D (gD) genes. All constructs contained a signal peptide that resulted in the secretion of the expressed proteins. In vitro, the characterization of the chimeric proteins indicated that both VP7 and gD retained their antigenicity and the C3d remained biologically active. However, immunization with plasmids encoding VP7-C3d chimeras did not enhance rotavirus-specific antibody responses and the frequency of BRV-specific IFN-gamma secreting cells in the spleens were significantly lower in mice immunized with pVP7-(C3d)(2) when compared with mice immunized with plasmid encoding VP7. The same pattern of immune responses was observed for plasmids encoding gD-C3d. Both gD-specific antibody responses and the frequency of gD-specific IFN-gamma secreting cells were significantly lower in mice immunized with plasmid expressing gD-C3d chimeras when compared with mice immunized with plasmid encoding gD alone. These results indicate that co-expression of C3d with an antigen actually inhibit both humoral and cell-mediated antigen-specific immune responses.

Encapsulation of rotavirus into poly(lactide-co-glycolide) microspheres

Two small-scale double emulsion techniques for incorporation of formaldehyde-inactivated rotavirus particles (FRRV) into poly(lactide-co-glycolide) (PLG) microspheres were developed and optimised. The effects of high-speed homogenisation versus vortex mixing on the double emulsion stability, microsphere size, entrapment efficiency and in vitro release of FRRV in the second emulsification step were studied. A stable double emulsion was verified only when using vortex mixing in this step. Slow removal of the organic phase allowed measurement of the size of the emulsion droplets and subsequent prediction of the size of the resulting microspheres. Microspheres in the size range of 1-10 microm were prepared using both techniques. The homogenisation technique was sensitive to changes in the operating time, the emulsification energy and the volume of the outer aqueous phase, while the vortex technique was more robust. Rotavirus was released in vitro in a triphasic manner with both techniques. The more robust vortex technique was selected for preparation of PLG microspheres containing rotavirus for in vivo studies. After immunisation of mice with a single intramuscular injection, the PLG-FRRV microspheres elicited an IgG antibody response in serum detected by ELISA equally high as that elicited with FRRV alone. These results indicate that the antigenicity of FFRV was retained after incorporation into PLG microspheres using the vortex technique.

The VP4 and VP7 of bovine rotavirus VMRI are antigenically and genetically closely related to P-type 5, G-type 6 strains

We have previously reported the isolation of a bovine rotavirus, designated VMRI, with a super-short electropherotype. We have characterized this strain further as it has shown antigenic differences with the prototype G6 strain NCDV-Lincoln. In this communication, we report the antigenic and molecular characterization and the nucleotide sequence of the VP4 and VP7 genes of this strain. Virus neutralization tests indicated 2- to 13-fold differences in the titers between NCDV-Lincoln, B641 and VMRI strains. Northern blot hybridization results indicated a degree of heterogeneity in the VP4 gene of these strains which can be detected under conditions of high stringency. The VP4 and VP7 genes of the VMRI strain were cloned and sequenced and compared with the published sequences of other bovine rotavirus strains. The VP4 gene of VMRI had a high degree of homology with that of UK and B641 strains but differed significantly from that of both NCDV-Lincoln and B223 strains. Sequence analysis of the VP7 gene of VMRI and other strains indicated a high degree of conservation and the amino acid identity between the different strains was 96%. Sequence information regarding these strains and field isolates will assist in the generation of effective vaccination strategies for control of neonatal calf diarrhea.

Evaluation of different methods (ELISA, IF, EM, PAGE) for the diagnosis of rotavirus infection in piglets

The study on the prevalence of rotaviral infections among diarrhoetic piglets in 11 commercial farms in Poland was carried out on 531 faecal samples tested using an ELISA to screen for rotavirus. Of these, 169 were found to contain rotavirus antigen (32% of all cases of diarrhoea tested). Those pig herds managed using the Bisprol system had a lower prevalence of rotavirus in pigs with diarrhoea than those faecal samples obtained from Gi-Gi or Agrokomplex Agard farms. To further establish the presence of rotavirus antigen, 28 of those positive in ELISA samples were taken for isolation of the virus using tissue culture; 18 (64%) isolates were successfully adapted into MA-104 cells and the presence of rotavirus confirmed by immunofluorescence (IF) and electron microscopy (EM). In addition, an analysis of the band patterns visualised on PAGE showed 9 distinct electropherotypes for rotaviral dsRNA among the tested specimens. These findings suggest that rotavirus may represent an important contribution to the incidence of diarrhoea in Polish pig herds. The use of ELISA technology provided an efficient and effective means of evaluating the presence of rotavirus antigen in faecal samples and indicates that this procedure is a very useful tool in epidemiological studies, but that other techniques are required to confirm the presence of virus.

Evaluation of a one-step test for rapid, in practice detection of rotavirus in farm animals

An immunochromatographic test for the detection of group A rotavirus was evaluated against a reference group A rotavirus ELISA, by using a panel of 161 bovine, porcine and equine faecal samples submitted for routine examination. The sensitivity of the test was 89 per cent and the specificity 99 per cent compared with the ELISA. Its reproducibility was 100 per cent. The simplicity and rapidity of the test procedure make it suitable for use in practice.